VI. NUCLEIN METABOLISM…

VI. NUCLEIN METABOLISM

No hard and fast line can be drawn between the metabolism of protein and that of nuclein. For though, morphologically speaking, the nuclei of cells are sharply differentiated from the circumambient cytoplasm, and exhibit equally distinct staining reactions, yet, chemically, the differences between them are quantitative rather than qualitative.

But while, as far as chemical changes are concerned, nuclein metabolism is comparable with that of protein, nevertheless the former in respect of its “energy” and its bearing upon growth and production, is infinitely more vital, incomparably more active; for it is in nuclear changes that we may best discern evidence of the initiation of oxidation processes and other varieties of enzymatic activity. Moreover, as Walker Hall points out, “the presence of masked iron phosphorus and certain forms of fat in the cell nucleus strengthens this view, and thus we are led to recognise the important part played by the nucleus in the life of the cell, and to appreciate the influence of nuclein heredity in cellular exchanges.”

So much by way of prelude, but the story of the growth of our knowledge of nuclein as opposed to protein is so fascinating as to be worthy of a slight digression.

THE ISOLATION OF NUCLEIC ACID

Functionally regarded, the nucleus is the essential element of the cell. Embedded within the cytoplasm, its isolation therefrom, and this in quantities sufficient for analysis, may well have dismayed the earlier workers. But the resources of Friedrich Miescher were equal thereto. Treating surgical bandages soaked with pus with a dilute solution of sodium sulphate, he extracted the heavy pus cells. These, then, by careful decantation, were easily disengaged. The pus cells, still intact, were then subjected to the digestive action of artificial gastric juice. The protoplasm was thus dissolved, but not the more resistant nuclei, which remained as an insoluble grey powder. In this manner cell nuclei, free from protoplasm, became available for chemical analysis. Treating the insoluble nuclei thus obtained with dilute sodium carbonate, a solution was formed. Acetic acid added thereto produced a flocculent precipitate which was found to contain phosphorus, and responded to protein colour tests. This substance Miescher christened by the name of nuclein. Subsequent observers prepared nuclein from the nuclei of yeast cells and the red blood corpuscles of birds. All nucleins are insoluble acids which form soluble salts with sodium. But while they respond to protein colour reactions they differ from protein in that they contain phosphorus and resist the solvent action of artificial gastric juice.

Migrating some ten years afterwards (1897) from Tubingen to Basle, Miescher entered upon his celebrated researches into the habits of the Rhine salmon. He found the belief had long been current that the fish, during their passage from the sea up the Rhine to their spawning haunts, never partook of food. That this belief was well founded he was able to prove; for, saving isolated and easily explicable exceptions, he noted that their alimentary canal was devoid of food débris, while their digestive juices were as a rule inert. One startling change he noted, that while, on the one hand, their muscular tissue profoundly wasted during their migration, their organs of reproduction enlarged enormously, the inevitable conclusion being that eggs and spermatozoa had been created from muscle protein.

RESEARCHES ON SPERMATOZOA

Struck by the opportunities for scientific investigation during the spawning season, Miescher determined to resume his work upon nuclein. Spermatic fluid or lachsmilch, being readily obtainable in great quantities, he had to hand a mass of material admirably adapted for chemical examination of the cell nucleus. The conclusion that the heads of the spermatozoa might be regarded as a metamorphosed nucleus seemed obvious, and the opportunity too good to be lost.

On examination he found the “sperm heads” protein-free, made up almost entirely of a single chemical entity, a salt of an organic base rich in nitrogen and an organic acid containing phosphorus. The former was protamine, the latter nucleic acid.

The presence of this salt protamine nucleate led to the conclusion that nuclein was merely a salt of protein and nucleic acid.

THE DISCOVERY OF PURINS

Miescher, who had already isolated nuclein and nucleic acid, came nigh to one other equally important discovery. Heating a specimen of protamine with nitric acid, he noted that a yellow spot formed which turned to bright red when moistened with alkali.

Alive to the import of the reaction, Miescher requested Piccard to examine salmon sperm for purin bases. Extracting the same with hydrochloric acid, Piccard found guanine, and what he thought was hypoxanthine, but which was in truth adenine.

Another distinguished worker in this sphere, Kossel, noted that, subjected to the action of hydrolytic agents, nucleins always yield purin derivatives; also that the same were derived, not from the protein of the nuclein, but from the nucleic acid. Thus it was to Kossel that we are indebted for the discovery of the purin bases, hypoxanthine, xanthine, guanine, and lastly adenine. It was, indeed, through his brilliant achievements that nucleic acid became recognisable as a definite entity, distinguishable from proteins and other body elements, this latter differentiation by token of the purin bases which are contained in nucleic acid.

Moreover, it led to the dissipation of the old belief that uric acid was an intermediate product of protein metabolism, for the revelation of purin bases as decomposition products of nucleic acid carried with it the inference that uric acid also had chemical affinities therewith. The chemical structure of the purin bases and that of uric acid betrayed a common likeness, and, therefore, a presumptive physiological connection; in other words, that a chemical nexus obtained between the cell nucleus or nucleic acid and uric acid.

The physiological derivation of uric acid from nucleic acid did not long lack experimental proof. In 1886 Minkowski found that, given extirpation of their livers, the urine of birds contained ammonium lactate, evidently a substitute for the uric acid normally present, notwithstanding the uric acid never entirely disappeared from the urine. This indicated the derivation of uric acid from two sources:—

(1) Conversion in the liver of ammonium lactate into uric acid. (2) Some other, though unknown, process of formation.

To clear up the obscurity regarding the latter, V. Mach, after extirpating the livers of geese, injected them subcutaneously with hypoxanthine, finding that the same was converted into uric acid, which was excreted in the urine. In this way the capacity of the organism to elaborate uric acid from a purin precursor was demonstrated.

URIC ACID A DERIVATIVE OF NUCLEIC ACID

Despite V. Mach’s revelation, the origin of uric acid from nucleic acid was still to seek. In the year following (1889) Horbaczewski traced it to this source, and in the following manner. Mixed with water, the pulp of the calf’s spleen was put to digest at 50° until putrefaction began. The fluid was then sterilised with a solution of lead acetate, and arterial blood being added it was kept at 50°, a current of air meanwhile being passed slowly through the mixture. Subsequently the fluid was found to contain uric acid; but the experiment being repeated, without the passage of air, xanthine and hypoxanthine and not uric acid resulted.

While Horbaczewski’s experimental findings were amply confirmed, some of his deductions therefrom were subsequently proved faulty. (Thus, he thought putrefaction an essential factor; also he believed that the formation of uric acid ensued before the purin groups were disengaged from the nucleic acid, and definitely affirmed that the uric acid was not produced by the oxidation of free xanthine or hypoxanthine.)

But, nevertheless, this pioneer established that in both man and rabbits uric acid was derived from nucleic acid. Also, having observed that when after starvation the food intake was resumed, a leucocytosis occurred, he announced his belief in the following theory. Thus, he noted that leukæmics, whose blood showed a high leucocyte count, excreted an unusually large amount of uric acid; consequently, he came to the conclusion that uric acid was formed from defunct leucocytes. Also that nuclein-rich food, when ingested, contributed to the formation of uric acid only in so far as it induced leucocytosis. Hence the origin of the increased uric acid excretion which occurs when feeding is resumed after starvation.

This increased excretion of uric acid after the ingestion of food rich in nucleic acid has been amply confirmed; but all the earlier attempts to achieve an increased excretion by the ingestion of free purin bases, as opposed to the combined purin bases, existing as such in nucleic acid, failed, although tried repeatedly.

So much for the various stages by which our knowledge of the purin derivatives of nucleic acid has been gradually acquired, for though purin bases had, from early times, been known to exist in animal tissues, their presence there could not be rationally accounted for prior to the discovery of nucleic acid.

It still remains for us to deal in detail with the further developments of our knowledge which concern the disruption of nucleic acid in the body and the process by which uric acid is derived therefrom.

But before proceeding to consider in detail the complex series or enzymatic transformation that this entails, it will, I think, be wiser to deal first with the chemistry of uric acid, its solubilities, and its sources, whether exogenous, endogenous or synthetic.

THE CHEMISTRY OF URIC ACID AND THE PURIN BODIES

Much of the vague philosophy of disease in past times may fairly be attributed to the complexity and mystery of action inherent in living matter. The subjects of physics, chemistry and biology, in their wider acceptation, were unevolved, and scientific pathology, the offspring of this ancestry, was yet unborn. How much we owe to physics, chemistry, and biology, those handmaids of medicine, is inestimable! But something at least of our debt thereto will be revealed in the following pages.

Of the purins in human urine, the most important is uric acid, and far behind comes xanthine, while traces of hypoxanthine, guanine, and adenine are also detectable. Some years ago the current view was that the metabolism of any protein gave rise to uric acid. This assumption has now proved to be erroneous, for it is known that only certain foodstuffs lead to an increase in the uric acid excretion; in other words, on a diet rich in purin the output thereof is considerably higher than on a purin-free diet, this being due to the large amount of nuclein and purin bases in flesh foods, especially those containing glandular substances. Under ordinary conditions the excretion of uric acid ranges from 0·3-1·2 gm. per diem, or 0·02-0·10 per cent. The oscillations in output vary with the state of health, diet, and personal idiosyncrasy.

CHEMICAL CONSTITUTION

The empirical formula of the uric acid molecule, C₅H₄N₄O₃, has for long been known, but it was reserved for Emil Fischer to reveal the chemical structure thereof. Through his labours we now know that uric acid is one of a group of substances which owe their kinship to their possession in common of the heterocyclic ring termed by Fischer the “purin nucleus” (1898).

The intimate relations of the purins of bio-chemical interest to the purin nucleus, and alike to each other, will be rendered more intelligible by examination of their structural formulæ as hereafter given. All, as will be seen, are derivatives of a synthetically formed body purin which, though unimportant in itself, is yet interesting in that it is the basic substance from which the following take origin:—

Purin C₅H₄N₄ Hypoxanthine C₅H₄N₄O Monoxy-purin } Adenine C₅H₃N₄NH₂ Amino-purin } Xanthine C₅H₄N₄O₂ Dioxy-purin } Purin Bases. Guanine C₅H₃N₄ONH₂ Aminooxy-purin } Uric acid C₅H₄N₄O₃ Trioxy-purin }

It now devolves upon us to note the arrangement of the atoms in the purin nucleus. To each atom is affixed a number indicating the exact location of the various atoms and groups attached to the said nucleus. The manner in which the various purin bodies are built up around the purin nucleus C₅N₄ will become apparent from a study of the following structural formulæ culled from Wells’ “Chemical Pathology”:—

STRUCTURAL FORMULÆ

N (1)—C (6) N CH C (2)—C (5)—N (7) HC C NH C (8) CH N (3)—C (4)—N (9) N C—N

Purin nucleus. Purin.

To describe the individual derivatives of purin we have to indicate to which particular atom of the purin nucleus the combining groups are attached. Thus, for example, adenine in structure is classed as a 6-amino-purin, and accordingly has the following formula:

N==C—NH₂ | | HC C—NH ‖ ‖ \ ‖ ‖ CH ‖ ‖ / N—C—N

Adenine (6-amino-purin).

Other important bodies built up round the purin nucleus C₅N₄, variously designated as xanthine, alloxuric and nuclein bodies:—

HN—C==O HN—C==O | | | | H₂NC C—NH O==C C—NH ‖ ‖ \ | ‖ \ ‖ ‖ CH | ‖ CH ‖ ‖ // | ‖ // N—C—N HN—C—N

Guanine Xanthine (2-amino-6-oxypurin). (2-6-dioxypurin).

HN—C==O HN—C==O | | | | HC C—NH O==C C—NH ‖ ‖ \ | ‖ \ ‖ ‖ CH | ‖ C==O ‖ ‖ // | ‖ / N—C—N HN—C—NH

Hypoxanthine Uric acid (6-oxypurin). (2-6-8-trioxypurin).

H₃C—N—C==O HN==C==O | | | | | | CH₃ | | CH₃ | | / | | / O==C C—N O==C C—N | ‖ \ | ‖ \ | ‖ CH | ‖ CH | ‖ // | ‖ / H₃C—N—C—N H₃C—N—C—N

Caffeine Theobromine (1-3-7-trimethyl, (3-7-dimethyl, 1-2-6-dioxypurin). 2-6-dioxypurin).

It will be seen that the purin bases stand in very close chemical relationship to uric acid in that the latter also is marked by the possession of a group called the purin nucleus; indeed, the relationship of uric acid to the purin bases is more intimate than to urea (CON₂H₄), close though this latter be as may be seen from the study of its constitutional formula. (For uric acid may be regarded as composed of two urea radicles, linked by a tricarbon chain. By oxidation and hydrolysis, two molecules of urea may be obtained from one of uric acid, and conversely uric acid is produced by the condensation of urea with hydroxy acids).

The first product of the oxidation of purin is hypoxanthine, long recognised as a constituent of meat extracts. Adenine, the amino derivative of hypoxanthine, is met with in combination with other substances in nuclear material. The second oxidation product of purin is xanthine, and its amino derivative guanine, both of which are found in the same substances as hypoxanthine and adenine. Further oxidation of purin gives rise to uric acid. We have to recognise, also, that in addition to the purins of animal origin there are some also derived from vegetables, viz., the methyl purins, caffeine, theobromine, and theine.

Now, as will be seen later, certain compounds, containing nitrogen and phosphorus, constitute the chief, if not the exclusive, source of uric acid. These substances, long known as nucleins or nucleo-proteins, exist in the animal tissues, and in special abundance in those largely made up of cell nuclei, viz., thymus, lymph-glands, etc. The important and, indeed, the distinguishing component of the nucleins or nucleo-proteins is nucleic acid. This, in that through the action of ferments, it is from the nucleic acids that uric acid and the purin bases are derived.

But, apart from this, we have to recollect that nucleic acids yield constituents other than purin bases, viz., the pyrimidine bases, phosphoric acid, and a carbohydrate group. From a study of the structural formulæ of the pyrimidine bases it will be seen that they are closely related to the purin bases, lacking, however, one of the urea radicles. Moreover, it is believed that, though included in the makeup of nucleic acid, they are not derived from purin but are primary products.

{ NH—CO { N==C—NH₂ { NH—CO Thymine { CO C CH₃ Cytocine { CO CH Uracil { CO CH { NH—CH { NH—CH { NH—CH

To sum up, the characteristic constituents of nucleic acid are the purin bases (adenine, guanine, hypoxanthine, and xanthine), pyrimidine bases (uracil, cytosine, thymine), phosphoric acid and a carbohydrate group.

We have now discussed the chemical structure of uric acid and its relationship to the purin bases; but before proceeding to consider the various sources from which uric acid is derived, it will I think be convenient to consider (1) the physical properties of uric acid and (2) the condition in which it circulates in the blood.

PROPERTIES OF URIC ACID

When pure, uric acid is white in colour and crystallises in rhombic form. In contrast to urea it is very insoluble, but much less so in blood serum than in distilled water, viz., ⅟₄₀₀₀₀ of water as opposed to ⅟₁₀₀₀ parts of plasma. It yields with alkalies two series of salts, viz., the biurate or mono-basic, and the so-called neutral or bi-basic urate, the latter of which is much more soluble. In water the mono-basic urate forms a colloidal solution from which the crystalline salt gradually precipitates.

The greater solubility of uric acid in blood plasma was, by Garrod and Haig, attributed to the alkalinity of the plasma. But it must be recalled that the earlier workers in this sphere judged of the alkalinity of the plasma by its reaction to litmus, a crude procedure as compared with the use of phenol-phthalein, and Frankel’s electro-potential measurements. Working with these as criteria, it has been shown that blood is normally alkaline in only a minority of cases, and indeed, according to Flack and Hill, the plasma is in reality neutral.

In the urine uric acid and the urates are held in solution by the neutral phosphates. This because the decomposition of the urates into uric acid by the acid salts of the urine is inhibited by the di-sodium phosphate present therein. Its maintenance in solution is possibly also reinforced through the influence of other constituents in the urine, notably, the urinary pigments and sodium chloride.

URIC ACID IN THE BLOOD

As to the form in which uric acid circulates in the blood, Sir William Roberts believed that when dissolved in blood serum it was transformed into the relatively soluble sodium quadriurate. This authority held that in gout, either through deficient excretion or over-production, the quadriurate accumulates in the blood. Circulating therein, in a medium rich in sodium carbonate, it takes up an additional atom of the base, and is transmuted into the biurate, which is less soluble and less easily excreted by the kidneys; consequently, the biurate is hoarded up in the blood, at first in gelatinous, and later in an almost crystalline form, when its precipitation is imminent or actually ensues. This, moreover, was apt to occur at sites where the circulation was poor, the temperature low, and more particularly in regions in which the plasma contained a relatively high percentage of sodium chloride, e.g., synovial sheaths.

But, unfortunately for the valency of this otherwise plausible theory, it was proved by Tunnicliffe, Rosenheim, and others, that quadriurates do not exist as definite chemical compounds; in short, it is generally conceded that their existence should no longer be accepted.

GUDZENT AND SCHADE’S THEORIES

Gudzent was of opinion that uric acid can only exist in the blood as the mono-sodium-urate, of which there are two isomeric varieties, the easily soluble unstable lactam, and the stable relatively insoluble lactim urate. It is the former, or lactam, variety that accumulates in the blood in gout and, according to Gudzent, it is the transmutation thereof into the lactim modification that determines the precipitation of urates in the tissues. The lactim urate is soluble only to the extent of 8·3 mg. per 100 cc. serum, whereas the lactam form is soluble up to 18 mg.

Others, like Bechhold, maintain that the urates are present in the blood in a colloidal form, impossible of excretion by the kidneys. Thus Schade contends that, in the presence of alkalies (hydrates), uric acid or its salts may pass into a state in which it is far more soluble than usual. Moreover, on its path to crystallisation from this over-saturated solution, it passes through a colloid stage in which it is relatively stable. The maintenance of this colloid stage and consequently the retardation of precipitation is promoted by certain substances, i.e., glycerine, urea, serum, albumen, nucleic acid, etc. But hitherto the therapeutic possibilities suggested have not been invoked.

ORGANIC COMBINATIONS

It will be recalled that purin bodies cannot be detected in the blood in health, though their administration by the mouth results in an increase in the excreta. Minkowski, to account for this, suggested that the purins in the blood were circulating in a combination which prevented them from giving the usual reactions, typical of their presence therein. We have an analogy in the masking of arsenic and iron in the cacodyl compounds and the ferrocyanide ion.[8]

The explanation proffered by Minkowski was elaborated by Von Noorden. His view was that lying at the disposal of the normal organism are a certain number of organic substances. These latter can combine with uric acid and render it soluble. It is then in this form passed through the blood in the kidneys, which eliminate from it the uric acid. Now, in gout these organic substances are deficient or wanting, and the result is that the uric acid is passed into the blood in the form of urates, the elimination of which only proceeds with difficulty; in other words, the purins normally circulate in organic combination and abnormally as salts of sodium.

It is worthy of note that, from a solution containing albuminous substances, Burian and Walker Hall found that while it was easy to remove the bulk of the purins, a certain percentage always remained which it was difficult to extract.

The view that uric acid is probably carried in the blood in combination with some other organic body and not, as was formerly supposed, with sodium salts, rapidly gained adherents, but the nature of the organic complex is still not accurately known. Many believe that at least a moiety of the uric acid circulates in combination with nucleic (thyminic) acid, but no such compound has yet been isolated from the blood. Nevertheless, as MacLeod suggests, this theory, were it proved correct, would account for the fact that some purins at least are katabolised in the body when they are given in a combined state, as thyminic acid, but are excreted unchanged when ingested in a free state. Thus, certain purins, e.g., adenine, when given freely, cause inflammation and calculous deposits in the kidneys of dogs which, however, does not ensue when they are fed with thymic acid.

But Walker Hall, discussing the good results obtained by Schmoll and Fenner from the administration of thyminic acid, states that his experiments do not indicate that the improvement is at all associated with any change in the uric acid excretion.

To sum up, it is obvious, from the mere variety of the hypotheses advanced, that we are still much in the dark as to the actual form in which uric acid circulates in the blood. While on the one hand the quadriurate theory appears no longer tenable,[9] on the other the nature of the suggested uric acid organic complex is still unknown.

Nay, more, Walker Hall, writing in 1913-14, states “there are many who consider that the sodium mono-urate is the only possible compound;” while Wells, in his “Chemical Pathology” (1918), claims that the best evidence points to uric acid existing in the blood “in a free state and not combined, as was at one time urged by several students of gout.”

COMPLEXITY OF THE PROBLEM

How complex, indeed, the task of the bio-chemist may be gathered from some reflections of Walker Hall. He reminds us that the oxidation and deaminisation of the nuclein derivatives, nucleins, nucleotides and nucleosides, is never complete. For purin bases and pyrimidin bases run side by side in the blood-stream together with uric acid. Also, that the unstable but soluble biurate is constantly changing into a less soluble type, viz., from one isomer to another. Moreover, since the red blood corpuscles abound in potassium, urates of potassium must also occur, and to these may be added, too, ammonium and calcium compounds in small quantities.

But more striking is his inference that the occurrence of isomeric forms of uric acid suggests that isomers of purins and pyrimidins also may occur. For the purin ring or pyrimidin nucleus, with their numerous receptors for the linking up of other substances, offer wide potentialities in the direction of isomerism.[10] Some of these, he hazards, may be born of one type of cell nucleus, some of another, while it is not inherently improbable that, “In response to abnormal stimuli or excessive demand, other isomers may be formed.”

Now, though uric acid and the urates can be extracted from the blood, it does not, as he remarks, necessarily follow that they circulate as such in vivo; for, despite modern achievements, “the best of the existing methods for the determination of uric acid in the blood are nearly barbarous in their crudity and intensity.” The various procedures available for such estimates fall short of distinction between the several tautomeric forms of uric acid, much less do they furnish any information as to the associations or combinations of purins or pyrimidins with other substances.

For himself, recognising the generally more complex nature of biological processes, he considers that “the circulation of the purins as sodium mono-urate and its simple extraction by kidney cells, seems almost too simple to be true.”

As to the solubilities of uric acid and urates in gouty blood he points out that the suspension capability of the blood-stream for uric acid much transcends the highest amount of uric acid as yet found in the gouty subject. Accordingly, to him, therefore, it seems that “neither chemical nor physico-chemical processes suffice to explain the problem. There must be something more, something vital, biological.”

Having ascertained as far as possible the measure of our knowledge in regard to the foregoing points, we shall, in the succeeding chapter, proceed to discuss the sources of uric acid, whether of intrinsic or extrinsic origin.

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VII. SOURCES OF URIC ACID

Uric acid, like the “purin bodies” (xanthine, hypoxanthine, guanine, and adenine), is derived from nucleins, i.e., from the breaking down of tissues rich in cells. The end-product of purin or nuclein katabolism uric acid represents but a further stage in the oxidation of the purin bodies. To the serial enzymatic transformations that mark its derivation from nucleic acid we shall allude later, but at this juncture we are concerned not with the mode of formation of uric acid, but with the sources thereof.

In this sphere we are greatly indebted to the pioneer researches of Burian and Schur. These observers noted that on a diet rich in nucleins (sweetbreads, liver, kidneys) the total daily excretion of uric acid was considerably higher than on a milk or purin-free diet. This difference in response to varying dietaries, in respect of the excretion of uric acid, led Burian and Schur to the conclusion that the purins excreted must be partly of exogenous and partly of endogenous origin; in other words, the exogenous purins are derived from the nucleins ingested in the food, whereas the endogenous are the outcome of the breaking down of the cellular tissue of the organism itself.

Here it may be noted that all the ingested purins are not excreted in the urine as uric acid, for some pass away as purins. Moreover, the amount excreted will vary with the kind of purin ingested, and also with the species of the animal that consumes it. Thus, in man “only one half of the hypoxanthine administered as such appears as uric acid in the urine, and but one fourth of the purin in nuclein when that is fed. In the dog, compared with man, about ten times as much purin disappears in its passage through the organism; in the rabbit, about three times” (Flack and Hill).[11]

In amount about 0·4-0·7 gramme of uric acid is excreted in human urine daily, and the purin bodies, hypoxanthine, xanthine, and adenine, in small quantities.

Beyond exogenous and endogenous purins there is yet one other possible source of uric acid, viz., its synthetic formation within the organism. This supposition took origin in Horbaczewski’s discovery that in the laboratory he was able to produce uric acid by the interaction of urea and glycocine, a finding afterwards confirmed by Latham. The theory was then advanced that a similar synthesis might be effected by the kidneys; but it was found that glycocine and urea, even when given in excess to mammals, caused no change in the uric acid excretion.

So much by way of preface to our detailed discussion seriatim of the various sources of uric acid, and to which we now pass on.

EXOGENOUS PURINS

The foodstuffs that cause an increase in purin excretion are divisible into three groups:—

(a) Amino-purins. (b) Oxy-purins. (c) Methyl-purins.

Amino-purins.—In man the taking of food rich in nucleated cells and therefore in nucleo-protein and nucleins, increases the quantity of uric acid in the urine. Thymus gland, pig’s pancreas, and herring roe, containing the characteristic conjugated proteins of nuclei, or Liebig’s meat extract, rich in purin bases, when ingested, lead to a distinct increase in purin excretion.

The researches of Kossel and Horbaczewski showed that such augmentation was mainly due to the production of uric acid from the nuclein substances of the food; in other words, it was due to the katabolism of nuclein, the cleavage products of which comprise adenine derived from thymus, and guanine from the pancreas, both of these bodies being amino-purins. According to Burian and Schur, of the amino-purins ingested, a fourth is excreted as purin.

Oxy-purins.—To this group belong xanthine and hypoxanthine. These substances occur in muscle, and in great abundance in meat extract, and Minkowski noted that the ingestion of xanthine bases markedly augmented the amount of uric acid excreted. In man, given ingestion of hypoxanthine as such, only one half thereof appears as uric acid in the urine. It may here be mentioned that not all the purin bases ingested exist bound up in the nuclein substances. An appreciable amount is present in the tissues in a free state, e.g., hypoxanthine in the muscles; consequently, a moiety of the intake of purin bodies, especially in the animal constituents of the food, is to hand ready formed, and does not require the disruption of nucleic acid for its liberation.

Methyl-purins.—The nuclei of vegetable cells also contain nucleo-protein, and, therefore, can add their quota to the purin intake. The most important are caffeine, theobromine, and theophyllin, the active principles of tea, coffee, and cocoa. It may here be recalled that of the purins administered in food, not all are excreted as uric acid, but some as purins. Now it is doubtful whether the methyl-purins lead to the formation of uric acid in the organism, or whether they are excreted as purin bases in the urine. According to Stewart, a fractional part of the purin bases in the urine is composed of heteroxanthine, 1-methyl-xanthine, and paraxanthine derived from the active principles of coffee, tea, and cocoa when consumed as beverages. As stated by Burian and Schur, one third of the methyl-purins ingested is excreted as purin.

From the foregoing data it will be obvious that the exogenous urinary purins are derived from nuclein and certain free xanthine bases, and that the influence of other nitrogenous foodstuffs in this direction is practically negligible.

EXOGENOUS URIC ACID EXCRETION

As to the amount of exogenous purins that, when administered orally, can be recovered from the urine, it would appear that a certain rough parallelism obtains between the purin content of the food and that of the urine. The amount of the exogenous urinary purin differs for different forms of food, a variation well illustrated by the following table, giving the results of Burian and Schur’s researches.

---------------+-------------------+---------------- | Total percentage | Percentage of Diet. | of purin | exogenous |substances in diet.| urinary purin. ---------------+-------------------+---------------- Beef | 0·06 | 0·030 Coffee | 0·20 | 0·075 Calf’s liver | 0·12 | 0·060 Calf’s spleen | 0·16 | 0·080 Calf’s thymus | 0·40 | 0·100 ---------------+-------------------+----------------

Walker Hall, experimenting with various purin-containing foods, found that (1) with chicken 54·4 per cent., (2) with plaice 58·7 per cent., (3) with beef 47·4 per cent., (4) with haricot beans 55 per cent. of the food purin appears in the urine as exogenous purin. These findings of Walker Hall’s, like Burian’s and Schur’s, reveal that, roughly speaking, 50 per cent. of the purin content in food is excreted in the urine.[12]

These figures must be taken as a broad average relating only to healthy individuals upon diets capable of perfect assimilation.

More recently, Mendel and Lyman found that about 60 per cent. of injected hypoxanthine, 50 per cent. of xanthine, 19-30 per cent. of guanosine, and 30-37 per cent. of adenine were excreted in the form of uric acid. While this is true of free purins, on the other hand, when bound purins, i.e., nucleins are administered, only a small proportion thereof appears as uric acid in the urine. But before proceeding to canvass the fate of the missing purin, it will, we think, be helpful if we interpolate here a table (Taylor and Rose), illustrative of the variations in uric acid excretion that attend a purin as opposed to a purin-free diet.

The subject of the experiment was, for three days, fed on a purin-free diet of milk, eggs, starch and sugar. At the end of this period a portion of the total nitrogen (3 grams) was administered in the form of sweetbreads, thymus gland, etc., with a high percentage content (0·482) of purin nitrogen. During the succeeding four days still more (6 grams) of the total nitrogen was replaced by sweetbread nitrogen. Subsequently the person was placed on the original purin-free diet.

---------------+-------------+--------------+-------------+-------------- |First period.|Second period.|Third period.|Fourth period. | Purin-free | | | Purin-free | diet. | | | diet. ---------------+-------------+--------------+-------------+-------------- Total urinary N| 8·9 | 8·7 | 9·1 | 8·8 Urea N and NH₂ | 7·3 | 7·1 | 7·1 | 7·05 Creatine | 0·58 | 0·55 | 0·56 | 0·47 Purin N (total)| 0·11 | 0·17 | 0·26 | 0·10 Uric acid N | 0·09 | 0·14 | 0·24 | 0·07 Remainder N | 0·91 | 0·88 | 0·18 | 1·18 ---------------+-------------+--------------+-------------+--------------

From a study of the table it will be noted that, following the introduction of sweetbreads rich in nucleins, the uric acid content of the urine markedly increased, to sink again when a purin-free diet was substituted. But it will be seen also, as MacLeod points out, that “the increase of uric acid accounted for less than half of the purin nitrogen ingested. This appeared as uric acid, the excretion of purin bases being practically unchanged.” In other words, a moiety of the bound purins, i.e., nucleins ingested, appears as uric acid in the urine.

FATE OF THE UNEXCRETED PURIN

As to what becomes of that portion of the ingested purin that, so to speak, disappears in the body, is largely a matter of speculation. As MacCallum states, “the liberation of guanine and adenine is well in the line of uric acid formation,” but “the fate of the pyrimidin groups, thymine and cytosine, is still uncertain.” According to this observer, Levene has hitherto been unable to find an enzyme which will decompose the nucleoside in which they occur, and that since they cannot form uric acid, they are possibly excreted as urea or in other forms. He adds that only 50 per cent. of the nucleic acid nitrogen can be counted on for the production of uric acid, viz., that in the guanine and adenine groups.

MacLeod, discussing this same point, suggests that some of the unrecovered purin may undergo decomposition in the intestine, but why so much should, after absorption of the blood, disappear is, as he remarks, difficult of explanation; for while uricase, which can decompose uric acid, exists in the tissues of the lower animals, no such ferment is found in man, and uric acid is excreted as such. According to MacLeod, too, “the destroyed purins cannot be shown to influence any of the other well-known nitrogenous metabolites of the urine.”

Lastly, Stewart, discussing the ultimate destiny of the absorbed products of nucleic acid digestion, suggests that, when undergoing further cleavages, “they may be in part utilised for the synthesis of nucleo-proteins, replacing those destroyed in the process of cell metabolism;” or, that it is “possible that they may be wholly disrupted into their components, and these again re-synthesised.”... “Finally, and this fate is probably not long delayed in the case of the surplus of purin compounds contained in ordinary dietaries, both the purins of the food and the purins arising from the waste of the tissues, are for the most part converted into uric acid and excreted in the urine.”

Also, it should be recollected that the purin bases normally found in human fæces are in part of exogenous origin, and are increased in amount after the ingestion of meat extract or thymus.

ENDOGENOUS PURINS

Even if we entirely eliminate all purin substances, by restricting the diet to purin-free foodstuffs (bread, milk, cheese, eggs and butter), purin in the form of uric acid is still excreted in the urine.

To this moiety the term endogenous purin is applied; for the continued excretion of purin on such a diet is explicable only on the view that they are derived from the waste of the tissues, the daily “wear and tear” of cells. In other words, it is the outcome of the katabolism of the nucleo-protein of the body tissues.

SOURCE OF ENDOGENOUS PURINS

Is the nuclear destruction of localised or generalised distribution?

Mares (and subsequently many other observers), having noted that, following the ingestion of purin-free protein food, a marked increase in endogenous uric acid excretion ensued, suggested that the said augmentation was the outcome of the “wear and tear” entailed upon the nuclear material of the secretory glands of the gastro-intestinal tract, following such intake.

The effects yielded on uric acid excretion by those antithetic drugs, atropine and pilocarpine, certainly seem to lend colour to Mares’ hypothesis.

Following the injection of atropine, the rise in uric acid output, that normally follows the ingestion of protein, was inhibited. But in sequence to pilocarpine, an excitant and not like atropine, a depressor of secretory activity, a marked increase in uric acid excretion followed. The contrast in response was naturally translated as striking evidence of the important rôle played by the digestive glands on uric acid excretion; in other words, it was held that the major portion of the endogenous uric acid was the reflex of such intensified glandular action.

In opposition, however, Burian, as the outcome of his experimental studies, maintained that a fractional portion only of the endogenous uric acid could be derived from the nucleo-protein of the body cells. This, inasmuch as it would entail a far too extensive katabolism of nuclear substance. Accordingly he propounded the view that the endogenous uric acid in the main was derived from the hypoxanthine of the inosinic acid present in muscular tissue. In this connection it may be noted that, on a diet approximating to Voit’s standard, 0·5 gram of purin is excreted daily. This, it is calculated, is equivalent to nearly 100 grams of thymus or allied tissue, which probably far exceeds the amount that could be gleaned from cellular katabolism.

PROTEINS AND THEIR DERIVATIVES

A comparison of the influence of proteins as contrasted with that of their digested products, the amino-acids, it was thought, might furnish a clue as to the extent of which the alleged activity of the digestive glands was responsible for the increased uric acid output that followed the intake of non-purin protein food.

Such was the supposition entertained by H. B. Lewis, M. S. Dunn, and E. A. Doisy. Alive, moreover, to the deficiency of the older procedure in use for the determination of small amounts of uric acid, Lewis and his collaborators invoked the more accurate colorimetric method of Folin and Denis (as modified by Benedict and Hitchcock).

The experiments were conducted with great care, and with as complete control as possible of the variable factors concerned. The investigators realised that, if any significance was to be attached to fluctuations in uric acid excretion following the intake of proteins and their derivatives, it was essential that accurate information be obtained as to the extent of the variations to be expected normally in the subjects when fasting. “Controls,” therefore, in which no food was consumed throughout the experiments, were instituted at frequent intervals so as to make sure that the level of endogenous uric acid metabolism was not altered by the long-continued purin-free diet.[13]

Passing now to the results obtained, it was noted that, after the intake of three types of purin-free protein food (egg white, cottage cheese, and glidine), there ensued a rise in uric acid output, reaching its maximum during the third or fourth hour after their intake. No quantitative differences in the uric acid output after ingestion of these three types of protein were observed; in short, the findings did but confirm what had been repeatedly demonstrated, viz., that the excretion of the endogenous uric acid is increased by purin-free protein food.

AMINO-ACIDS AND DICARBOXYLIC AMINO-ACIDS

But the further interesting fact emerged, viz., that glycocoll and alanine, end-products of protein digestion, also augmented uric acid excretion; moreover, this even more swiftly than proteins, the maximum being reached within two hours after their intake.

In addition, like results followed the ingestion of the dicarboxylic amino-acids (glutaminic and aspartic acids), the increase in endogenous uric acid excretion being even more pronounced than with glycocoll or alanine.

Now, it must be recalled that the amino-acids represent the end-products of protein digestion. Accordingly, Lewis and his co-workers argue that “since no digestive processes are required for the utilisation of amino-acids, it can hardly be considered that the rises in endogenous uric acid observed following the ingestion of four different amino-acids can be attributed to the work of the digestive glands.” The effect, they held, is more probably attributable to “a direct stimulation of the body cells by amino-acids or their katabolism products, a stimulation of nuclear metabolism,” for it is known that amino-acids disappear very swiftly from the blood-stream to be stored up temporarily in the tissues.

The question that now confronted the observers was whether the stimulation of nuclear metabolism was an inherent property of amino-acids. If so, “substituted amino-acids might be expected to exert a similar influence.” But, if on the contrary, it was due not to the amino-acids as such but “either to the cellular work of their katabolism or to the intermediary products of their breakdown, a substituted amino-acid which does not follow the normal path of amino-acid catabolism would in all probability be devoid of the power of stimulation.”

To this end, they selected sarcosine or methyl-glycocoll to elucidate the point at issue; this, inasmuch as it has been found to pass through the organism for the most part unchanged. The result justified their inference, for no perceptible influence on uric acid excretion was noted. Hence, on the basis of this experiment, they inferred that the stimulation of uric acid metabolism was not an inherent property of amino-acids; in other words, that if an amino-acid when ingested does not undergo disruptive katabolism, it is without effect on uric acid excretion.

Now deaminisation is the first stage in the katabolism of amino-acids, yielding as products ammonia and a-ketonic or hydroxy acids. The ammonia thus formed normally undergoes conversion into urea and is excreted as such. In order to ascertain whether the ammonia stimulated uric acid excretion, ammonium chloride was administered, but no rise in the uric acid output above the normal level ensued. Also, the ingestion of urea seemed to entail no appreciable increase in the uric acid elimination; in other words, these katabolic products of the nitrogenous moiety of the amino-acids are without effect. As to the non-nitrogenous intermediary products of the katabolism of amino-acids, i.e., the a-ketonic or hydroxy acids, it was impossible to investigate the influence of these on the endogenous uric acid elimination.[14]

Lusk also has brought forward evidence that in the presence of amino-acids cellular activities are intensified markedly. According to Taylor and Rose, too, not only nuclear katabolism, but also nuclear anabolism, may be accelerated by the presence of large amounts of amino-acids.

Lewis and his collaborators consider that the results of their researches militate against Mares’ hypothesis, viz., that the origin of the increased amounts of endogenous uric acid that follow the intake of purin-free protein stuffs is referable to intensified activity of the digestive glands.

They hold that “it can be accounted for equally well as the result of a general stimulation of all cellular metabolism by the products of digestion of proteins the amino-acids.”

The recorded increases in endogenous urinary purin are, they consider, far too great to be the outcome of the stimulation of so small a proportion of the cells of the body as those of the digestive tract. On the other hand, they do not deem it necessary to assume that the whole of the endogenous uric acid is the outcome of nuclear disruption, concurring with Burian’s view, that a moiety thereof may be derived from the hypoxanthine of muscular tissue.

ENDOGENOUS URIC ACID EXCRETION

The researches of Leathes and his collaborators permit the deduction that endogenous uric acid excretion bears a definite relation to the activity of cellular processes. Given unchanged physiological conditions, e.g., muscular exercise, the amount of the endogenous uric acid excreted is, for the same individual, fairly constant, and this irrespective of diet; but it is not the same for different individuals, even those of identical body weight.

According to MacLeod, the endogenous excretion in an adult man fluctuates between 0·12 and 0·20 per cent. purin nitrogen. The average daily endogenous uric acid output of a normal adult, as stated by Walker Hall, is about 0·5 gram, while that of a gouty individual is 0·45 gram.

Now Burian and Schur’s original contention was that, in a given individual on a purin-free diet, the endogenous purin output was constant, and this despite marked variations in the amount of the purin-free food digested.

Recent researches, however, of Folin and of Hopkins and Hope, indicate that this dictum must be modified to this extent, viz., that although it is true that the endogenous excretion continues remarkably constant, with moderate variations in the amount of purin-free food, it is not so in the presence of marked variations.

The subject (Hopkins and Hope), after a fast of six hours, was given a meal of bread and potatoes, and at every subsequent hour estimates were made of the amount of urea and uric acid excreted in the urine.

------------------+--------------+--------------+-------------- | | Uric acid. | Amount of Time. | Urea. Grams. | Milligrams. | urine. C.C. ------------------+--------------+--------------+-------------- 10-11 | 1·07 | 26 | 175 11-12 | 1·13 | 27 | 118 12-1 p.m. | 1·07 | 24 | 164 1-2 (meal). | 0·64 | 21 | 60 2-3 | 1·12 | 22 | 43 3-4 | 1·16 | 38 | 41 4-5 | 0·84 | 40 | 53 5-6 | 1·16 | 56 | 59 6-7 | 1·20 | 39 | 56 7-8 | 1·37 | 30 | 95 8-9 | 1·47 | 33 | 183 9-10 | 1·33 | 24 | 155 10-11 | 1·33 | 23 | 180 ------------------+--------------+--------------+--------------

It is clear from the results obtained that a very definite increase of endogenous purin excretion ensued, and that the said increase occurred sooner as regards uric acid than urea. This bears out what Mares demonstrated many years ago, viz., that the greatest increase in uric acid excretion occurs in a few hours after a meal, whereas the increase in the case of urea comes more tardily, not reaching its maximum until some hours after.

Horbaczewski referred such increase in uric acid excretion to a digestive leucocytosis; in other words, that the uric acid was the outcome of destruction of the leucocytes, and consequent formation of purin from the released nucleic acid. Unfortunately for this theory, the period of most marked augmentation in uric acid excretion ensues when the leucocytes are most in evidence in the blood-stream, not after they have disappeared, as would be the case if uric acid was derived from the purin product of the nucleic acid liberated by leucocytic destruction. We have a parallel instance in the case of pneumonia, in which it has been shown that the elimination of uric acid and other purins is at its acme when the leucocytes are most abundant; in other words, the highest uric acid output coincides with the period of most marked leucocytosis, whereas during the post-critical stage, viz., when leucocytes are being destroyed in great numbers, the output of uric acid is very markedly lowered. Discussing Horbaczewski’s theory in light of the above criticisms, MacLeod suggests, “that the facts appear to indicate that the purin substance is a metabolic product of the living leucocytes,” and not, so to speak, the chemical outcast of their disruption and death.

Lastly, Walker Hall, discussing endogenous uric acid excretion, emphasises the necessity of discriminating between the uric acid output and the total purin output. He reminds us that the actual cell nucleins belong chiefly to the group of amino-purins, i.e., guanine and adenine, and that the oxypurines, xanthine and hypoxanthine, are intermediate products on their way to excretion, another and more advanced intermediate product being uric acid. Now, only a proportion of these intermediary products appears in the urine, this commonly cited to be approximately 50 per cent.

But this, as Walker Hall states, must be taken only as a very broad estimate, for in the same individual the output varies with the number of conditions, not as yet fully determined. But the point most emphasised by him is, that though “the uric acid output varies considerably, the total purin output does not show similar variations; for when the uric acid excretion wanes that of the purin bases usually rises. As a consequence, the total purin output is more constant, less influenced by circumstances, than the output of uric acid.”

This being so, we shall now pass on to consider other conditions influencing endogenous uric acid excretion.

FACTORS INFLUENCING ENDOGENOUS URIC ACID EXCRETION

The output of endogenous uric acid excretion is influenced by (1) Physiological conditions, (2) Pathological states, and (3) The ingestion of certain drugs.

PHYSIOLOGICAL CONDITIONS

It is now recognised that the purin bases of the body exist not only in the bound form (nucleic acid), but also free, especially in muscular tissue. Also, that from such free purin bases uric acid can be readily formed as from those liberated by the disruption of nucleic acid. Thus, inosinic acid, a nucleotid first isolated from meat extract, yields phosphoric acid and the purin base, hypoxanthine. In possession of these facts, we shall be better able to appreciate the significance of the researches of Burian and others.

(a) Muscular Exercise.—According to Burian a large increase in the excretion of uric acid was found to follow muscular exercise. The same observer also noted the presence of hypoxanthine in defibrinated blood after its perfusion through the hind legs of a dog whose muscles had been thrown into tetanus. Moreover, subsequent to contraction, the muscles themselves contained an increased amount of oxypurine. From these findings Burian concluded that hypoxanthine was a product of muscular action, and that this substance or its precursor, inosinic acid, was an important source of endogenous uric acid. The uric acid thus formed by oxidation was then partly destroyed in the liver and partly excreted by the kidneys. But Burian noted also during activity of the muscles that a certain amount of the purin bases failed of oxidation, and consequently a larger amount of the same, as compared with uric acid, passed into the circulation.

Kennaway, discussing the effect of muscular exercise on the excretion of endogenous purins, noted that during unaccustomed exercise the uric acid output of the kidneys diminished, but that of the purin bases is relatively augmented, but, on the whole, he found that the total purin output (bases plus uric acid) was not very much increased.

Leathes and others, investigating the effects on uric acid excretion of strenuous exercise, established the occurrence of a distinct increase. Given that the same kind of exercise is practised on the day following, the said increase is much less marked. If, however, some different form of muscular activity is undertaken, another increase in uric acid follows. It would appear, therefore, that, despite conflicting evidence, the balance of opinion favours the view that muscular activity does lead to increase in endogenous uric acid excretion.

(b) Periodic Variations.—Leathes noted diurnal and nocturnal variations in the excretion of endogenous uric acid, the maximum occurring within the early waking hours, and sinking to a minimum towards the evening. His experiments, he held, indicated a variation in the actual formation of endogenous uric acid at different periods of the day. Rockwood also found that an increase occurred during the daytime, and Pfeil, that there was a morning rise in the amount of uric acid passed. The fact that doubt still obtains as to whether muscular exercise has any effect on endogenous uric acid excretion, renders explanation of this diurnal variation difficult. This especially as there are no fluctuations in the urinary functions that could in any way account for it.

PATHOLOGICAL STATES

Endogenous uric acid is increased under certain pathological conditions. Leathes’ recent work confirmed the view that there is an increased production of nitrogenous waste in fevers. After taking a large dose of anti-typhoid serum his temperature rose to 103° F. Experimenting on himself, he found his output of urea, uric acid, and creatinine all increased, but of all three uric acid showed the most marked alteration. The question now arises as to whether such is due to increased production or diminished destruction. Some further experiments conducted by Leathes on himself may serve to elucidate this point. Subjecting himself for a prolonged period to cold baths, a similar increase in his uric acid output ensued. This would appear to indicate that, through increased loss of heat, the bodily processes of combustion were augmented to maintain the body temperature, with, as a consequence, increased uric acid excretion.

In leukæmia protein-destroying forces are at work, and the urine contains large quantities of uric acid. The same is attributed to the formation and destruction of enormous numbers of leucocytes, but the urinary findings in this respect have been extremely variable. While increased uric acid elimination has been vouched for by many authors, some have noted increase in the purin bases, sometimes with, and sometimes without increase in the uric acid; while others again have even noted a decrease in uric acid and phosphoric acid excretion.

Apart from these contradictory findings, it would appear, according to Magnus-Levy, that in acute leukæmias the relation between the number of leucocytes and the uric acid output is most variable. Lastly, the different types of leukæmia present differences in regard of their uric acid output, the increase in the myelogenous variety being much more marked than in the lymphatic form.

Wells, discussing these conflicting data, considers that they are but the reflex of the “known fluctuations in the course of the pathological processes of leukæmia; the number of leucocytes, the size of the lymphatic organs, and the general condition of the patient all vary greatly from time to time, often with remarkable rapidity and the excretion of products of metabolic activity must vary likewise.” Continuing, he observes that the enormous increase in the amount of lymphoid tissue in the body and blood must give rise to a greatly augmented nuclein katabolism, with sequential appearance of uric acid, purin bases, and phosphoric acid in the urine. This he holds to be well demonstrated by the increased elimination of uric acid and purin bases, together with a general increase in the nitrogen output such as has been frequently noted in sequence to the therapeutic use of X-rays in leukæmia, this attributable to the increased autolysis known to be induced by X-rays.

As to this question of the relationship of leucocytosis to uric acid excretion, it must be borne in mind that the number of leucocytes and the excretion of uric acid do not always vary directly. Parallel studies of the blood and urine have shown that leucocytosis does not invariably accompany increased uric acid excretion. Indeed, Hutchison and MacLeod have recorded cases of leucopenia without any reduction in the amount of uric acid eliminated.

Also, we have to recall that on a purin-free diet the amount of endogenous uric acid is more than can come from nuclein destruction in the body. As suggested by Burian, some may be derived from the hypoxanthine in muscular tissue. In short, while nuclein disintegration is the outstanding source of endogenous purin, yet, for the reason cited, it cannot be regarded as the sole source, for the exact origin of all the endogenous purin is not as yet established.

In conclusion, it would appear that some drugs influence more or less markedly the excretion of endogenous uric acid, notably, atophan; but discussion of these will, we think, be best postponed to the section dealing with the medicinal treatment of gout. Meanwhile we shall proceed to consider the vexed question of the formation within the organism of uric acid by synthesis.

SYNTHETIC FORMATION OF URIC ACID

Birds eliminate most of their nitrogen in the form of uric acid, and, undoubtedly, in their instance synthetic formation of uric acid in the liver takes place on a large scale. Thus, when blood containing ammonium lactate is perfused through the liver of the goose, an increase in the uric acid content of the blood occurs. Also the ingestion of lactic, pyruvic and other organic acids leads to augmented output of uric acid; in short, it is generally agreed that in birds synthesis is the chief mode of formation of uric acid, homologous with the formation of urea in the liver of mammals.

If this be true of birds, on the other hand, splitting and oxidation of nucleins is in mammals the most important source of uric acid, but there is evidence that it cannot all be accounted for in this way. As before remarked, the old belief that purin excretion remains almost constant on a purin-free diet, despite great variations in the amount of the ingests, is not strictly true. Thus, using swifter and more reliable methods for the estimation of nitrogenous metabolites, Folin noted, on an absolutely purin-free diet, that an increase in purin excretion ensued, given marked variations in the intake of food. Again, the Dalmatian dog, as we have seen, excretes uric acid in his urine. S. R. Benedict was therefore able to demonstrate that a very distinct increase in his uric acid output ensued in sequence to increase in the amount of his non-purin food; moreover, that even when such non-purin foods were continued for a year, “the total amount of uric acid excreted was at least ten times greater than could have come from the traces unavoidably included in the food” (MacLeod).

Also Ascoli and Izar, experimenting with dog livers, noted on incubation thereof and passage through the same of oxygen that the uric acid disappeared; but on the substitution of carbon dioxide an accumulation thereof ensued. Wells, however, was unable to confirm this re-synthesis of uric acid by dog livers, and Spiers also failed to corroborate their findings.

On the other hand, there is evidence pointing to the fact that a certain small percentage of synthetic formation does take place in the organism. Thus certain chemical substances, and these not purin, do cause an appreciable though slight increase in the purin excretion of mammals, and a very marked augmentation of the same in birds, viz., lactic, tartronic and B-oxybutyric acids.

But, as MacLeod, discussing these experimental and clinical findings, observes, there are to hand even more direct proofs that purin synthesis occurs in mammals. Thus, as McCallum has pointed out, we cannot escape the admission that young mammals are able to synthetise the purins essential for their growth, and this from food containing no purin, e.g., milk. Again, prior to incubation, a hen’s egg contains practically no nucleic acid, whereas after development its content in the same increases by great strides. The eggs of insects, too, with the progress of development, amass purin very rapidly.

Again, Miescher noted long since that salmon, on leaving the sea to ascend rivers for the object of spawning, have at that time well-developed muscles; but on arriving at the upper reaches, marked muscular wasting ensues, while the testes undergo enormous enlargement. MacLeod, reflecting on these observations, argues that, “as the fish takes no food during the migration, there must be conversion of the protein of the muscles into the cellular tissue of the sexual glands, and nucleic acid must be produced.” MacLeod’s conclusion is that “Purin synthesis undoubtedly occurs in the mammalian body, but it is difficult to recognise in metabolism investigation, because it is a slow continuous process ... whether or not changes in the activity of purin synthesis occur in conditions of disease, is a question which awaits investigation.” Lastly, the opinion of most authorities is that, while they concede the possibility of synthetic formation, the amount of uric acid produced in this manner is negligible, and that by far the most important mode of formation in mammals is by the splitting and oxidation of nucleins; in other words, that uric acid in the main is derived from the amino-purins by deaminisation and subsequent oxidation, and from the oxy-purins directly by oxidation.

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VIII. FORMATION AND DESTRUCTION OF URIC ACID

The chemical structure and sources of uric acid having been dealt with, we are now in a position to resume our narrative, and to take up the thread at the point when Horbaczewski revealed the derivation of uric acid from nucleic acid. It now devolves upon us to scrutinise more narrowly the process by which the formation of uric acid from nucleic acid is achieved. Incidentally, it will not be unprofitable to note, if only briefly, the steps by which the necessary expansion of our chemical and physiological knowledge of nucleic acids has been acquired.

As may be imagined, the primary difficulty was to prepare nucleic acids of such purity as admitted of their elementary chemical analysis. The necessary researches were to a large extent confined to two types of nucleic acid, one derived from yeast, and the other from the thymus gland; in other words, to representatives of the only two nucleic acids in nature, one derived from the nuclei of animal cells, the other from the nuclei of vegetable cells.

A feature common to nucleic acids of animal and vegetable origin is that, on hydrolysis with boiling mineral acid, they yield two purin derivatives, guanine and adenine, and a pyrimidin derivative, cytosine. From thence as regards their remaining constituent elements they display distinctions. Thus animal nucleic acids yield thymine, and contain a hexose group in their molecule. On the other hand, vegetable nucleic acids give forth uracil and possess a hexose group.

To sum up, nucleic acid is a chemical complex, made up of phosphoric acid with purin bases, pyrimidin bases and carbohydrate radicles. Moreover, nucleic acids, whatever their source, show a striking similarity in structure, containing always two amino-purins (adenine and guanine), two pyrimidines (either cytosine and uracil, or cytosine and thymine), and a carbohydrate. Now, while purin bases are always present, yet, in respect of their carbohydrate group, nucleic acids display variations; this, according as they are of animal or vegetable origin. If the former, the carbohydrate group is a hexose (contains six carbon atoms) with thymine. If the latter, it contains pentose (five carbon atoms) with uracil.

The constancy in the content of the various nucleic acids is such that Levene and Jacobs have felt justified in putting forward the following provisional formula as to the constitution of a nucleic acid of animal origin.

DISTRIBUTION OF THE ENZYMES

The enzymes responsible for the disruption of the nucleic acid complex are not to be found in all the body tissues. Moreover, the distribution of the enzymes in the various organs and tissues varies in different species of animals. Of the various organs the liver, spleen, thymus, and pancreas more particularly contain enzymes in abundance. As to their varied location in different animals, it may be noted that the enzyme responsible for the oxidation of xanthine into uric acid, viz., xanthine-oxidase, is found in man only in the liver. In other animals, also, it is of localised distribution, being as a rule only found in the liver or in the liver and kidney. The dog, however, appears to be an exception, xanthine-oxidase being found in a variety of its tissues.

Adenase, the deaminising enzyme, is not to be found in any organs in man. Neither does it exist in any of the tissues of the rat. Consequently, if adenine be injected subcutaneously in rats, it undergoes oxidation, without abstraction of its amino group.

On the other hand, guanase, also a deaminising enzyme, is in man to be detected in the kidney, lung, and liver, but not in the pancreas or spleen. In the pig, however, guanase is lacking, and its absence no doubt explains why deposits of guanine may occur in the muscles constituting the so-called guanine gout met with in swine. It is worthy of note also that in pigs’ urine the content of purin bases exceeds that of uric acid.

To sum up, in man the enzyme, xanthine-oxidase, which forms uric acid from xanthine, is located chiefly or exclusively in the liver. This, of course, represents the final stage of purin metabolism, but the antecedent chemical processes involved in the disruption of nucleic acids are initiated by the action of enzymes in the intestinal juices and wall, and to a consideration seriatim of these changes we now proceed.

STAGES IN DISRUPTION OF NUCLEIC ACID

As might be expected from the complex structure of the nucleic acid molecule, a number of ferments are concerned in its disruption. The gastric and pancreatic juices contain not a trace of any enzymes. Thus, when nucleo-protein is subjected to the gastric juice a moiety of protein is readily split off and hydrolysed to peptone and other products of proteolysis.

But the nuclein element remains unacted upon until it comes under the action of the pancreatic juice. Hydrolysis then ensues, and the ingested nuclein is broken down into nucleic acid and protein. The nucleic acid remains unaffected by the pancreatic juice, but, coming in contact with the succus entericus, it undergoes partial decomposition through the action of a ferment called nuclease or nucleic-acidase. Under its disruptive effect the nucleic acids or poly-nucleotides are further split up into groups known as nucleotides. The two pyrimidine nucleotides split off and undergo no further change. But, through the action of another ferment, nucleotidase, the purin nucleotides are further decomposed to yield nucleosides (substances of the glucoside class made up of a combination of a purin base with a carbohydrate group of the nucleic acid with which also phosphoric acid is linked).

No further stage in hydrolysis of nucleic acid occurs in the intestine, but the nucleosides are again in turn split up after reaching the tissues, particularly in the spleen, liver, and thymus. This, under the action of specific enzymes, nucleosidases, which succeed in breaking the nucleosides down into the so-called “building stones” of the nucleic acid molecule, phosphoric acid group, carbohydrate group, pyrimidine and purin bases, especially adenine and guanine. The adenine and guanine thus formed are, by the action of the ferments adenase and guanase, converted and, by the removal of their amino group, transformed, adenine into hypoxanthine, and guanine into xanthine, thus:—

C₅H₅N₅ + H₂O = C₅H₄N₄O + NH₃; C₅H₅N₅O + H₂O = C₅H₄N₄O₂ + NH₃ Adenine. Hypoxanthine. Guanine. Xanthine.

By the action of oxidases also present in the tissues hypoxanthine is changed into xanthine and xanthine into uric acid (trioxy-purine), this by a specific ferment xanthine oxidase.

C₅H₄N₄O O—C₅H₅N₄O₂; C₅H₅N₄O₂ O C₅H₄N₄O₃ Hypoxanthine. Xanthine. Xanthine. Uric acid.

It will be seen that the disintegration of nucleic acid involves many stages, and its complexity is such that we make no apology for drawing upon the masterly monograph of Walter Jones for further elucidation of this intricate question. In relating the history of nucleic acid in the animal body Jones has found it convenient to introduce certain terms wherewith to designate the various elements of the nucleic acid molecule. Thus, the molecule in its entirety is termed a tetra-nucleotide. The cleavage of this complex is initiated by the action of two specific enzymes. Through their agency the tetra-nucleotide is first cloven into two di-nucleotides, which immediately divide up into four mono-nucleotides. These ferments are:—

(1) Phospho-nuclease (which splits off the phosphoric acid radicle, leaving a nucleoside, guanosine or adenosine).

H₂PO₄—C₅H₈O₃—C₅H₄N₅O + H₂O----->H₃PO₄ + C₅H₉O₄—C₅H₄N₅O Guanylic acid. Phospho-nuclease. Guanosine.

(2) Purin-nuclease (which splits off the purin radicle, viz., separates out both phosphoric acid and carbohydrate groups, leaving free purin bases).

H₂PO₄—C₅H₈O₃—C₅H₄N₅O + H₂O----->H₂PO₄—C₅H₉O₄ + C₅H₅N₅O Guanylic acid. Purin-nuclease. Guanine.

Now, in sequence to either of the foregoing cleavages by the phospho- or purin-nucleases another set of enzymes come into the field. Under their deaminising effect the amino group is abstracted, with the formation of either free oxy-purins or oxy-purins still bound in glucoside-like combination with sugar.

If the oxy-purins are free, the following is the reaction:—

C₅H₅N₅O + H₂O------>C₅H₄N₄O₂ + NH₃ Guanine. Guanase. Xanthine.

Should, however, the guanine glucoside be present:—

C₅H₉O₄—C₅H₄N₅O + H₂O------>C₅H₉O₄—C₅H₃N₄O₂ + NH₃ Guanosine. Guanosine-deaminase. Xanthosine.

In the latter instance a hydrolysing enzyme, xanthosine-hydrolase, by its action, splits off xanthine. We see, therefore, that by either route the end-product is the same. Following a like series of changes, the adenine radicle is transmuted into hypoxanthine. This either directly by the action of adenase:—

C₅H₅N₅ + H₂O------>C₅H₄N₄O + NH₃ Adenine. Adenase. Hypoxanthine.

or indirectly through the agency of adenosine-deaminase, the hypoxanthine-glucoside (inosine) is formed, and subsequently the hypoxanthine is split off.

Xanthine and hypoxanthine are, therefore, now to hand, and given the presence of oxygen, their oxidation to uric acid ensues:—

C₅H₄N₄O + O---------------------> C₅H₄N₄O₂ Hypoxanthine. Hypoxanthine-oxidase. Xanthine.

C₅H₄N₄O₂ + O----------------->C₅H₄N₄O₃ Xanthine. Xanthine-oxidase. Uric acid.

Now, in man and the anthropoid apes, uric acid is the end-product of purin catabolism. In contrast therewith in most mammals only a minimal amount of the exogenous or endogenous purins escapes in the urine as uric acid. Most of it undergoes further oxidation into allantoin,[15] this change taking place in most mammals chiefly in the liver. According to Schittenhelm, if nucleic acid be given to dogs, pigs or rabbits, from 93-95 per cent. thereof appears in the urine as allantoin, and only 3-6 per cent. as uric acid, and 1-2 per cent. as purin bases.

In man, as in most mammals, uric acid is formed chiefly in the liver from purins, and in the preceding table Amberg and Walter Jones schematically represent the various steps by which disruption of the nucleic acid molecule is attained, and uric acid formed.

DESTRUCTION OF URIC ACID

Uricolysis, or the destruction of uric acid, is, in most mammals, achieved through the agency of the oxidising enzyme uricase, which oxidises uric acid to allantoin. Consequently, in their instance, purin bases, ingested as such or set free in the tissues, appear in the urine, not as uric acid, but in the form of allantoin. On the other hand, both in man and in the anthropoid apes, this particular enzyme uricase is absent. In accordance therewith, only a trace of allantoin is to be found in the urine of man and the higher apes, while in the lower animals, e.g., dogs, pigs, and rabbits, a large proportion of the purin excretion assumes this form.

Now, the absence of uricase, in man, is held to be proved by the fact established by Wiechowski and others, viz., that uric acid, if injected subcutaneously, may be almost wholly recovered in the urine, and moreover, unchanged. On the other hand, the total excretion of uric acid and the other purin bodies by no means tallies exactly with the amount of the uric acid ingested as purin bases in the food and that produced from the tissues; in other words, it has been found that, when given by the mouth, nucleic acid or purins are by no means quantitatively excreted in the urine, even though not only uric acid, but also allantoin and the purin bases, are included within the estimate. According to most experiments, a considerable proportion of the purin-nitrogen intake, about 50 per cent., is excreted as urea.

The question then arises as to what becomes of that moiety of the food purins which fails to appear in the urine as uric acid. Now the amount of allantoin that appears in the urine is negligible. Moreover, Ackroyd, having shown that the organism cannot destroy allantoin, it is possible that the minimal amounts excreted thereof in the urine are all derived from the food.

Accordingly, if, as experimental feeding with purins or nucleic acid appears to indicate, purins are destroyed in the body they “pass through some other route than allantoin, and possibly, that part of the purin which is destroyed does not pass through the stage of uric acid.” Such is Wells’ opinion, and he reminds us that in vitro the destruction of uric acid can be attained by other routes than through allantoin. Thus, it can be broken down into glycocoll, ammonia, and CO₂, or by another method of disintegration it furnishes first alloxan (C₄H₂N₂O₄), then parabanic acid (C₃H₂N₂O₃), which in turn yields oxalic acid and urea.

But while it is probable that there is more than one way in which uric acid can be decomposed in the body, nevertheless there is, according to Wells, no evidence that either of the alternative routes above suggested is ever affected in the animal body. In this impasse Siven suggests the further possibility, viz., that the moiety of the food-purins which fail of recovery from the urine undergo partial destruction in the intestine by bacteria.

Stewart, however, in his “Physiology,” discussing uricolysis, maintains that a considerable destruction of uric acid and other purin bodies goes on in the body and mainly in the liver. He reminds us that when uric acid is heated in a sealed tube with strong hydrochloric acid, it breaks down into glycin, carbon-dioxide and ammonia, and he maintains that “there are grounds for believing that a similar decomposition takes place in the body, and that the products are then transformed into urea in the liver”; this, through the agency of a special ferment called the uricolytic enzyme.

Also, Flack and Hill, discussing the metabolism of nuclein, hold that some of the uric acid thus formed may be transmuted into urea by an uricolytic ferment present in the liver, muscles, and kidneys. This same agent they consider “probably destroys a considerable amount of the uric acid formed in the body. Indeed, uric acid, even when given in the food, owing to the presence of this enzyme, causes no increase in the uric acid output of the body.”

On the other hand, Wells, discussing the destruction of uric acid, observes that repeated investigations show “that the tissues of man have no power whatever to destroy uric acid in vitro; the earlier reports of positive uricolysis undoubtedly being erroneous.” His final conclusion, after weighing all available evidence, is that it is highly probable that in man “most of the purin absorbed from the food, and practically all the purin from cell metabolism, is converted into uric acid and excreted as such.” MacLeod, however, reflecting on the fact that uric acid is not destroyed when extracts of the organs are incubated at body temperature with uric acid or its precursors, bids us bear in mind that, “although the uric acid is thus shown not to be destroyed in vitro, it may nevertheless be destroyed in the living animal.”

We see, therefore, that the question, Whether uric acid can undergo destruction in the human body? is still a matter of dispute, and must, pending further investigation, remain sub judice. Still, despite the conflict of evidence, clinicians have felt justified in assuming that one of the factors in the genesis of gout may be an entire absence or a diminution in the amount or activity of this uricolytic ferment.

But the awkward fact remains that all researches up to date have failed to establish the presence in the human body of any enzyme which can decompose uric acid. Should, therefore, future investigators place beyond the reach of cavil the claim that no uric-acid-destroying enzyme exists in the body, it would seem that, ipso facto, man, through lack of this capacity for rapid oxidation of uric acid, is, by this same disability, rendered a potential victim of uric acid retention and deposition.

Elucidation of this vexed point seems more probable in view of the striking discovery recently made by R. Benedict, viz., that in one particular breed of dog, the Dalmatian, uricase is wholly absent. In respect of this lack of a uric-acid-destroying ferment, the Dalmatian breed of dog has a purin metabolism apparently identical with that of man.[16] Thus, if fed on a purin-free diet, he passes large quantities of uric acid, and if the latter be injected subcutaneously, elimination in quantity as such ensues; this, in striking contrast to what obtains in all other animals in whom, as before noted, uric acid is mostly oxidised to allantoin before excretion. Now, as MacLeod observes, investigation into the metabolism of nucleic acid has, in man, been hampered greatly, in that the absence of uricase from his tissues, prior to Benedict’s discovery, rendered experimental researches on the lower animals valueless. But, in light of the above revelation later by R. Benedict, it may reasonably be hoped that in the near future our knowledge as to the location and nature of the intermediary chemical processes occurring in the metabolism of nucleic acids may be materially clarified.

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IX. URIC ACID IN RELATION TO GOUT

It will be recalled that at the close of our chapter on Pathogenesis we referred to the growing scepticism of Garrod’s views as to the pathogeny of gout. Still, if we except Edward Liveing’s pertinent observation that uricæmia was not peculiar to gout, naught, save alternative hypotheses, unsupported by pathological data, was advanced. Consequently, Garrod’s facts never being seriously called in question, his position remained unassailable, until, in the year 1898, his original observations as to the lowered alkalinity of the blood in acute gout, and the increased uric acid content thereof during the same, were definitely contradicted by Magnus Levy.

Working with more modern and more reliable methods of technique, this observer, in a series of seventeen cases of acute gout, found no evidence of any lessening in alkalinity of the blood or of any augmentation of its uric acid content as compared with the inter-paroxysmal period.

Again, as to Garrod’s claim that there was a diminished excretion of uric acid during the attack, this also, while supported by Minkowski, was called in question by Pfeiffer, Levy, and Badt, who found the reverse to be the case, i.e., a notable increase in the excretion of uric acid during the paroxysm.

These results were again in 1900 confirmed by Chalmers Watson. An exhaustive study of a series of cases of acute gouty polyarthritis convinced him that:—

(1) The alkalinity of the blood is not diminished during the attack.

(2) The excretion of uric acid is not lessened during the paroxysm, but the reverse; there is, therefore, no ground for the supposition that there is a temporary diminution in the capacity of the kidneys to excrete uric acid.

(3) The amount of the uric acid in the blood is not greater during the attack than in the intervening period, and if these points be accepted, we must start de novo in search of the cause of the acute paroxysm.

The iconoclastic revelations of the foregoing researches may well form a preface to our discussion of gout from the triple aspect of:—

(1) Uric acid excretion. (2) Uricæmia. (3) Uratosis.

URIC ACID EXCRETION IN GOUT

The earlier investigations as to the behaviour of uric acid in the organism were necessarily restricted to the noting of any variations in the uric acid output in the urine. That the findings and, alike, the deductions proved bewilderingly contradictory is not to be marvelled at when we recall the many factors that govern the amount of uric acid excreted in the urine.

How fallacious, it now transpires, were the assumptions based upon the mere uric acid output in the urine, and how little understood even to-day the many conditions that determine its variations.[17] But, fortunately, we can now to some extent control and review our urinary findings in light of the uric acid content of the blood. But we anticipate, and meanwhile let us confine our discussion to the variations in uric acid excretion that occur in gout, and this as revealed by more modern students of the disease. This will be more conveniently dealt with if we consider first the oscillations in uric acid output in relation to acute attacks of the disorder, and subsequently the same as met with in its more chronic manifestations.

URIC ACID VARIATIONS IN ACUTE GOUT

Generally speaking, there appears to be a consensus of opinion on the following points:—

(1) That in the intervals between acute attacks of gout the elimination of uric acid lies within the normal limits, but that

(2) For one or two days prior to an acute attack an appreciable decline in the output of uric acid occurs. This, however, is not so marked as the subsequent

(3) Increased output of uric acid during the acute attack. According to Magnus Levy the increase may reach from 0·3-0·5 gram, daily, and more, and may sometimes last for a week or even two.

(4) Following attack a tardy decline in uric acid output to former level.

To sum up, during an attack of acute gout the uric acid output stands at a relatively low level between the paroxysms. But one or two days before the oncoming attack a diminution in uric acid output ensues. In contrast with the outbreak of the attack, the uric acid excretion increases markedly, this enduring for a week or more, when the output again declines. The augmented output during the paroxysm is more constant than the diminished excretion antecedent thereto. Now, while it may be taken that the foregoing variations in uric acid output, prior, during, and subsequent to, acute attacks, obtain as a general rule, such behaviour is not invariable; for, unfortunately, as Wells reminds us, instances are met with in which “the uric acid excretion shows no variation from that of normal persons.”

URIC ACID VARIATIONS IN CHRONIC GOUT

It must never be forgotten that the elimination of uric acid displays wide variations, this even when the subject under investigation is on a constant diet. Consequently, as Folin has pointed out, “even in the case of gout, which is distinctly associated with uric acid, it is an extremely difficult matter to prove by means of urine analyses that the uric acid elimination is not entirely normal.” And he adds, “If it had not been for the fact that uric acid, because of its insolubility, is so easily found in the joints, it would unquestionably have been a very long time before any definite relationship between uric acid and gout could have been established.”

None can gainsay the truth of these reflections, for, when placed on a fixed diet, the uric acid output in the victims of chronic gout differs but little from that of normal individuals on a similar regime; save in this respect, that, following the intake of purin-containing substances, the period of augmented uric acid excretion that ensues is prolonged as compared with the normal.

RETARDED EXOGENOUS URIC ACID OUTPUT

In 1901 Vogt showed that in gout the excretion of exogenous purins was not only delayed but diminished. Giving simultaneously to a gouty subject and a healthy individual a diet rich in purins, he found that, in the former, retention and delayed excretion of purins ensued. Vogt’s findings were confirmed by Reach, Soetbeer, Pollak, Mallory, and others.

Brugsch and Schittenhelm also observed that, following the intake of purin-containing substances, the exogenous uric acid excretion was retarded and reduced; in other words, the percentage of exogenous nitrogen excreted as uric acid nitrogen is less than in normal individuals, although the increased elimination extends over a longer period of time.

On the other hand, Walker Hall finds that, though there is retardation, there is no diminution in the output in gouty subjects. Thus he states: “When an adult takes a meal consisting of half a pound of beef and a quarter of a pound of sweetbread, containing about 0·620 gram purins, the moiety which usually occurs in the urine, say 0·300 gram, is not fully excreted until 6-10 hours have elapsed. When a similar meal is taken by a gouty individual the full 0·300 gram is eliminated, but the rate of output is delayed, some 48-72 hours being necessary.”

The same observer states that, given intravenous injection of acid into a normal man, its elimination is spread over several days, and the total amount injected fails to appear in the urine. But if the injection be administered during a course of atophan, then the uric acid excretion is completed within twenty-four hours, and the whole amount injected can be recovered from the urine. Now if in a gouty subject the same method of procedure be adopted, the sequence of events is precisely similar, and like results have been reported, following the administration of sodium salicylate to vegetarians of five or more years’ standing. To sum up, the above findings would appear to indicate that:—

(1) A gouty subject can excrete exogenous purins as adequately as a normal man, but he takes longer to do so.

(2) If the extra purins be taken during a course of atophan, even this departure from normal is obliterated, i.e., the customary delay in excretion is obviated.[18]

But, unfortunately for the diagnostic valency of this symptom in gout, viz., retarded exogenous purin output, it has not been found to be invariable. Thus Magnus Levy has shown that, in some instances of gout, the elimination of exogenous purin is neither reduced nor protracted. Pratt, too, has confirmed this observer’s findings, while, as we shall see later, this authority, also McClure, Mallory, and others, have placed on record the still more disconcerting fact, viz., that a diminished and retarded output of exogenous purin is not peculiar to gout.

The inference then would appear to be that:—

(1) Reduction and retardation of the excretion of exogenous purin, though common in gout, is not invariable.

(2) The same is not peculiar to gout, but occurs in other disorders.

(3) Its diagnostic valency, as a characteristic feature of gout, is correspondingly depreciated.

LOWERED ENDOGENOUS URIC ACID OUTPUT

As a rule, gouty subjects, on a purin-free diet, excrete less endogenous uric acid than normal persons. Thus, according to Walker Hall, the average daily endogenous urinary uric acid output of a normal adult is about 0·5 gramme, while that of a gouty subject is about 0·45 gramme. Brugsch and Schittenhelm hold that in about 80 per cent. of cases the average endogenous excretion is lower than normal.[19]

According to these same observers, “the maximum fluctuation during attack-free periods was at first believed to be less than in the normal cases; more recent examinations, however, have shown that in the same case of gout there may be periods of high, and periods of low, endogenous uric acid excretion.” These variations, they hold, are not to be accounted for by either mild or severe attacks of gout, for they occur in the attack-free period.

Again Laird, investigating the elimination of endogenous uric acid in a case of chronic gout, noted that the output thereof was sub-normal, and, as Brugsch and Schittenhelm observed, the same presented marked variations. The leucocyte counts he found normal, but the phosphorus output and the acidity were sub-normal. Bloch again, while he agrees that endogenous purin excretion is usually below the average in gouty subjects, found that the output thereof is at its minimum before an acute attack of gout.

The foregoing observations would suggest that the retention or delayed excretion of uric acid applies both to exogenous and endogenous purins. But, when we come to analyse the foregoing findings as to the variations in uric acid output, both in acute and chronic gout, one feels inclined to agree with O. Folin, “that the clinically useful contributions obtained by urine analysis have not been very numerous.” Thus we cannot, on the basis of the variations in uric acid excretion, presume to diagnose gout; in other words, if we take urine analysis alone, it is extremely difficult to prove that the uric acid elimination in gout is really and truly abnormal. Our uncertainty, moreover, is the more pronounced when we realise that in some cases of rheumatoid arthritis, etc., there is a disturbance of purin metabolism which in some of its features is reminiscent of that obtaining in typical gout. But, before proceeding to discuss this interesting resemblance, it will, we think, be convenient here to recall that the obliquities in metabolism found in gout are not wholly restricted to uric acid.

OTHER ANOMALIES IN EXCRETION IN GOUT

As Levene and Kristeller have shown, side by side with the delayed excretion of ingested purins, there occurs also a tardy elimination of the other nitrogenous products of protein food. Vogt observed that fluctuations in nitrogen retention and nitrogen loss are quite typical of gouty subjects. As to the why and wherefore, however, of this variability, it remains a mystery. Nor do we know the form in which the nitrogen is retained, though Vogt maintains that the uneliminated moiety takes the form of purin bodies. According to Brugsch, it is during the acute attacks of gout that the nitrogen loss reaches its zenith, and he suggests that the nitrogen retention in the inter-paroxysmal periods is in part compensatory. On the other hand, the gain in weight that ensues is not adequate to account for the sum total of the nitrogen retention; while, as before observed, in gout there occurs, not only retarded elimination of exogenous purins, but also of other nitrogenous products of protein food. Yet, according to Heffter, the ratio of purin bases to uric acid is unaltered in the urine of gouty subjects.

Again, all nucleins contain a phosphoric acid group, and Futcher found that the curve of the uric acid output ran in a striking parallel with that of phosphoric acid. But the attempts of subsequent investigators to show that the two end-products of nuclein disintegration—uric acid and phosphoric acid—go hand-in-hand prove contradictory. Hence Wells, in regard to phosphoric elimination, observes that, “it seems probable that it shows no characteristic alterations in gout.” Lastly, we will recall to the reader that in the chapter on protein metabolism it was pointed out that the amino-acids, especially glycocoll, are found in excess in “gouty” urines.

In conclusion, it must, we fear, be admitted that the results of urinary analyses have proved insufficient of themselves to unravel the intricacies of metabolism in gout, and, after a brief digression, we shall proceed to ascertain whether, on the other hand, chemical analysis of the blood by modern methods can in any way shed further light on this obscure problem.

PURIN METABOLISM IN OTHER DISORDERS

Working at the Research Hospital for the Study of Special Diseases at Cambridge, Strangeways (1910) commented on the striking resemblance that obtained between certain cases of so-called rheumatoid arthritis and gout, as evidenced by X-ray findings and section of the joints. Their similitude in these respects suggested that the nature of the apparent kinship of the two disorders might be elucidated by a study of purin metabolism in instances of rheumatoid arthritis.

To this end Ackroyd studied the purin metabolism in eleven persons, the victims of rheumatoid arthritis. His conclusion was that there was no important variation from the normal. To quote his own words, he states that “it may be (1) completely normal, or (2) while normal as regards endogenous excretion, the period of increased uric acid excretion which follows the administration of hypoxanthine may be prolonged for more than four days. It is more likely that this effect is individual, than that it is characteristic of any particular form of the disease, excepting those cases in which the prolongation is accompanied by active manifestation of the disease.”

W. J. Mallory, critically analysing Ackroyd’s cases, points out that he used only hypoxanthine in his studies; also that, while hypoxanthine has this advantage, that it is of definite and known chemical composition, furnishing a known quantity of basic nitrogen, it labours under this drawback: “It is by simple oxidation converted into uric acid, and probably calls into action only a limited part of the ferment system concerned in the formation of uric acid.” As a consequence, therefore, the amount of information on metabolism that can be gleaned through its usage is more restricted than if nucleinic acid were invoked in its place; for this substance, on the other hand, calls into action all the various enzymes concerned in the disruption of nuclein or nucleic acid.

Alive to these advantages, Mallory, in addition to hypoxanthine, used nucleinic acid in his investigations of purin metabolism in a series of eight “undoubted cases of so-called rheumatoid arthritis.” The value of the inclusion of nucleinic acid is revealed by the fact that some of the cases, when given exogenous purin in the form of hypoxanthine, showed no deviation from the normal. On the other hand, when given nucleinic acid, a prolongation of the period of increased uric acid excretion ensued; this even though the total amount of basic nitrogen in nucleinic acid is less than in hypoxanthine. Thus 4 grams of nucleinic acid have 0·2632 gram of basic nitrogen, while 0·75 gram hypoxanthine has 0·309 gram of basic nitrogen.

Apart from his own series of cases, Mallory analysed those of other observers, and his conclusions are as follows: “Of nineteen cases of rheumatoid arthritis in which the purin metabolism has been studied by three different observers, nine cases, or 47·3 per cent., show a marked variation from the normal in their reaction to purin-containing substances while they are on a purin-free diet.

“In these cases the period of increased uric acid excretion which follows the administration of purin-containing substances is much prolonged. Following the administration of purin-containing substances, a considerable number of cases suffer from attacks of sub-acute arthritis, accompanied in some cases by an increased uric acid excretion.”

It will be seen that in virtue of:—

(1) The prolongation of the period of exogenous uric acid excretion, and

(2) Increased uric acid excretion during attacks of sub-acute arthritis,

certain cases of rheumatoid arthritis manifest a certain resemblance to gout, though, as Mallory remarks, “other features characteristic of that disease are lacking.”

It may be observed that the attacks of sub-acute arthritis that ensued in rheumatoid subjects followed the administration of hypoxanthine, as shown in Ackroyd’s series. That this reaction to exogenous purin is suggestive of a relationship between rheumatoid arthritis and gout derives colour from the fact that it has been repeatedly induced in gouty subjects by the same means. Thus, Brugsch and Mallory (1910), after giving 0·5 gram of hypoxanthine to a gouty patient, noted a typical outbreak of gout. Again, Brugsch and Schittenhelm, in the same year, reported attacks of arthritis following the administration of nucleinic acid to gouty subjects.

Another feature worthy of note is that, in the cases of rheumatoid arthritis investigated by Ackroyd and Mallory, the percentage of exogenous purin nitrogen excreted as uric acid nitrogen largely exceeds that observed in any case of gout available for comparison by these authors.

Mallory’s final conclusions were that “there seemed to be sufficient data to show that, in certain cases of so-called rheumatoid arthritis, the purin metabolism is not normal. Whether these cases are real gout, or only resemble that disease in certain features, must be determined by further studies.”

PURIN METABOLISM IN CHRONIC ALCOHOLISM AND PLUMBISM

Quoting from Mallory’s contribution, we note that Pollak investigated the purin metabolism in a series of cases of chronic alcoholism. In five of the examples a marked derangement of purin metabolism was noted and manifested, “partly in retention, and partly in delayed excretion, or a combination of the two.” Having observed these variations in cases of what he considered were non-gouty alcoholics, Pollak felt justified in attaching but limited diagnostic import to the results of the examination of uric acid metabolism in gout, this though he realises the importance of alcoholic excess as a cause of disturbed purin metabolism.

Mallory’s observations, too, on uric acid excretion in gout complicated by lead poisoning are highly interesting. In two cases of this nature he noted that the percentage of uric acid nitrogen excreted was relatively small—in this respect in full accord with previous observations of Brugsch and Schittenhelm on a gouty patient with a history of plumbism, with this reservation, that in the latter observers’ example there were indications of early renal disease, while in Mallory’s two cases such was absent, the urine being normal, and likewise the blood pressure.

Again, Pollak in a case of lead gout noted an extremely low endogenous average, viz., a daily average endogenous excretion of 0·06 gram uric acid in a period of five days. Eschemburg, quoted by Pollak, has recorded an instance of gout with plumbism in which the excretion fell as low as 0·02-0·04 grams. It may be noted that Pollak’s was the victim also of incipient renal disease.

Reverting to Mallory’s conclusions, this observer’s studies of examples of gout with lead poisoning seem to indicate that “these cases differ from normal persons to a greater degree than do other cases of gout.” It may, he thinks, be affirmed that the subjects of gout and plumbism, as a rule, show “some or all of the following characteristics in a much more marked degree than do cases unassociated with lead”:—

(1) Slight fluctuation in the endogenous excretion.

(2) Low endogenous average.

(3) Small percentage of exogenous purin nitrogen excreted as uric acid nitrogen.

To sum up, then, we see that poisons, other than those responsible for gout, may engender obliquities of general metabolism, with disturbances of purin assimilation and output, viz., lead, alcohol, and the causa causans of rheumatoid arthritis. Also, in respect of lead poisoning and alcoholism, further affinities with gout are discernible in that, like the latter disorder, they tend in their later stages to be associated with arterio-sclerosis and renal inadequacy.

INFANTILE GOUT

Apart from the fact that gouty arthritis may occur in young children, Comby and other observers have noted that children born of gouty parents display a tendency to inflammatory changes in the cutaneous tissues and also in the mucous membranes.

These proclivities are difficult of explanation, but some further observations by Czerny, Paltauf, Escherich, and Pfaunder are also worthy of note. Under the headings of “exudative diathesis” or “neuro-lymphatismus” they have described a symptom complex marked by lymphatism with asthma, occasional vomiting, defective nervous equilibrium, and eosinophilia. These varied phenomena also are common in the descendants of gouty, diabetic, and arthritic subjects.

The clue to the true nature of these phenomena may possibly reside in the fact noted and emphasised by Uffenheimer, viz., that these children exhibit a purin metabolism identical with that met with in gouty patients.

From the foregoing consideration it is clear that further observations are called for in the sphere of purin metabolism, and it is, perhaps, not too much to hope that extended investigations of the uric acid content of the blood may clarify and illumine the conflicting results obtained by urine analysis.

As before stated, we had intended in the next chapter dealing with the question of “Uricæmia in Gout,” but on second thoughts it appears desirable to us to interpolate a chapter devoted to discussion of the primary renal origin of gout; for we take it that, with the phenomena of uric acid excretion in gout fresh in our minds, it will be more easy at this juncture to attempt solution of this very intricate problem. This achieved, we shall resume our thread and pass to the consideration of uricæmia and subsequently uratosis in gout.

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X. THE RENAL THEORY OF GOUT

This time-worn hypothesis as to the pathogeny of gout has, perhaps, provoked more controversy than any other etiological problem in the sphere of clinical medicine. Nor, unfortunately, despite the endless laborious research expended upon its solution, the dialectic skill exercised in attempts at its elucidation, can we claim even to-day that its complexities have been wholly unravelled. But, perhaps it will be wiser to postpone decision, pending detailed analysis of the several grounds upon which the theory of the primary renal origin of gout rests.

Broadly speaking, the arguments adduced tend to concern themselves with or rather to arise out of certain apparent abnormalities in uric acid excretion, currently held distinctive of gout, certain resemblances also suggestive of a hidden nexus between gout and renal disorders, viz.:—

(1) Anomalies in uric acid excretion in gout.

(2) Uricæmia, a condition common to gout and nephritis.

(3) Uratosis, a feature also common to both disorders.

(4) Occasional co-existence of gout and nephritis.

ANOMALIES IN URIC ACID EXCRETION IN GOUT

As to the variations in purin excretion that occur in gout, it must be admitted that, notwithstanding the magnitude of the researches, no very striking departures from normal have emerged. Such as have been elicited occur in relation to (a) the acute paroxysm, (b) the excretion of exogenous purin.

The Acute Paroxysm.—Garrod, it will be recalled, claimed that during an acute attack of gout the excretion of uric acid was diminished, and that coincidently therewith the uric acid blood content rose. But these findings in the blood and urine, which constituted the basis of his hypothesis that gout was due to renal inadequacy, have, as previously noted, been categorically disproved.

Turning to the more modern findings upon which such refutation of Garrod’s view was achieved, one point emerges that appears to favour the assumption of renal block. It is that, one or two days prior to an acute attack, an appreciable decline in the output of uric acid occurs.

But this, be it noted, is neither so marked nor so constant as the subsequent increase; in short, at the zenith of an acute attack, an augmented output of uric acid ensues. At the very time when presumably the alleged functional renal impediment would be most pronounced, the impermeability of the organs for uric acid accentuated! Surely such behaviour seems scarcely compatible with the supposition that there is even a temporary diminution in the capacity of the kidney to excrete uric acid. Does it not in truth constitute strong proof of the reverse? Moreover, the said vagaries that herald the oncoming and that chequer the course of the paroxysm are not invariable, an obvious caveat against hasty etiological inferences therefrom. Any tendency thereto should also be curbed by the reflection that, viewing the character of the uric acid excretion in gout as a whole, the variations therein are not more extensive than in healthy individuals, and assuredly, on the mere basis of the fluctuations in uric acid excretion, no diagnosis of gout is possible.

Retarded Purin Elimination.—The mainstay in argument, however, as advanced by more modern advocates of the renal theory of gout, is that a retarded output of exogenous purin is typical of this disorder; but, here, again, there is no room for dogmatism. Thus Walker Hall reminds us that “the quantity of purins present in the food does not overstep the solubility of urates in the blood-stream, for once the material is metabolised and ready for removal the amount of blood, so far as solubility goes, places the whole amount of purins within the reach of the renal cells in less than twenty-five minutes.” We see, therefore, as far as rapidity of transport to the kidneys is concerned, there is no delay in presentation of the opportunity for the excretion of exogenous purin. While the alleged tardiness of output is attributed to defective action of the kidneys, it is at least equally possible that the delay, as Walker Hall states, “may be due to a defective or idiosyncratic nuclear metabolism, which results in the formation of isomeric purins or incomplete purin combination, and which makes greater demands upon the selective activities of the renal cells;” for it must be recollected that as yet we are ignorant as to the exact form in which uric acid circulates in the blood-stream, whether as sodium mono-urate or in organic combination.

Moreover, experimental injections of uric acid into the tissues or veins show no impairment in the elimination capacity of the kidneys for uric acid. Thus, Wells cites evidence that “the kidney in gout shows no lack of ability to excrete uric acid injected into the tissues.”

Again, given intravenous injection of uric acid into a normal man, its excretion occupies several days, and it fails to appear quantitatively in the urine. But if administered during a course of atophan, then the whole amount injected is excreted within twenty-four hours. If the same procedure be followed in a gouty individual, precisely the same results are obtained; in other words, both normal and gouty kidneys react in identical fashion to atophan. Given an inherent functional defect, quâ uric acid excretion, in the gouty kidney, one would scarcely expect a wholly normal reaction thereto. Surely some disparity would be disclosed, some aberration in response as compared with normal renal organs.

Again, while McLester and others claim that atophan exerts “a selective stimulating influence on uric acid excretion,” it is quite possible that its rôle may be otherwise explained. May it not influence the actual formation of uric acid, or, failing this, the form in which it is presented to the kidneys for excretion? Nicolaier and Dohrn, indeed, believe that atophan influences in some way purin metabolism within the muscles and so leads to increased formation and excretion of uric acid. At any rate, whatever be the explanation of the action of atophan, the fact that healthy and gouty kidneys react alike thereto cannot be interpreted as proof of defective capacity for uric acid elimination in gouty subjects, indeed the reverse.

Moreover, in all our attempts to saddle the kidneys with the responsibility for the delay in exogenous purin excretion, we are for ever hampered in that we know not whether the alleged renal impairment is primary or secondary to the gout. That the kidneys are frequently functionally inefficient in the later stages of gout may be conceded. But what of the initial phases of the disorder? Some talk very glibly of subjects who are, they say, “potentially gouty.” But has the rate of disposal of ingested purins been investigated in persons suffering from so-called “goutiness,” or, perhaps more pertinently, in those individuals, not uncommon, who, while exhibiting auricular tophi, have yet experienced no frank attack of gout?

In this connection we may note that McClure has recently emphasised the fact that the kidneys, in the later stages of gout, are often functionally deficient, and that, accordingly, the faulty elimination of exogenous uric acid by gouty persons may be simply the result of such functional renal depression; in other words, not due to gout, but to the secondary or associated renal deficiency. Hence, having regard to the frequency with which renal inefficiency is met with in gout of any standing, he is inclined to discount the value of studies of exogenous uric acid elimination as an aid to the diagnosis of gout. Consequently, he holds that before the diagnostic status of retarded purin elimination, as a symptom of gout, can be established, an investigation of the output of uric acid in the different types of nephritis is essential.

From the foregoing it will be seen that we stand in urgent need of further studies of early or oncoming gout and of early nephritis before we can with certitude impeach the kidneys as responsible for the delay in exogenous purin output. Meanwhile, too, we must be careful not to overlook the further disconcerting fact, previously adverted to, that the retardation and diminution of exogenous purin output is not invariable in gout. Nor, for that matter, is it peculiar to gout, considerations both of which, if confirmed, will still further discount the diagnostic significance of this phenomenon.

URICÆMIA IN NEPHRITIS

Von Jaksch and Klemperer noted long since that in chronic interstitial nephritis urates are always present in the blood. Now, according to Folin and Denis, human blood contains 1·5-2·5 mg. of uric acid per 100 c.c.; but if the eliminating powers of the kidney be deficient, the uric acid content thereof rises, sometimes to as high as from 15-20 mg. per 100 c.c.

But more interesting still the fact noted by Fine, viz., that even in early interstitial nephritis the same feature is well marked, i.e., the blood may contain 4-8 mg. of uric acid per 100 c.c. Indeed, according to this authority, increase in the uric acid content of the blood is the first signal of impaired renal efficiency. This, be it noted, without any coincident proportional increase in the blood content of urea or creatinine. The sequence would appear to indicate that the damaged organ encounters greater difficulty in excreting uric acid than these other metabolites.

But, pari passu with the advance of the renal disease, retention of urea is superadded, and still later creatinine. So constant, indeed, the sequence that, by determining the percentage amount of these three metabolites in the blood, the measure of the renal mischief may be gauged.

But of striking significance is the further point established by Myers and Fine, viz., that the blood content, in respect of uric acid, urea, and creatinine, in early nephritis, is an almost exact replica of that met with in typical cases of gout. The same is well illustrated in the following table, in which the blood content, in respect of these three metabolites, in cases of gout and early and late nephritis is contrasted. The percentage of the retained metabolites in relation to the severity of the case is gauged by the blood pressure findings.

URIC ACID, UREA N, AND CREATININE OF BLOOD IN GOUT AND EARLY AND LATE NEPHRITIS

===========================+=====+===========+===========+========= |Uric | Urea N. |Creatinine.|Systolic Diagnosis. |acid.|Mg. to 100 | | blood | |c.c. blood.| |pressure. ---------------------------+-----+-----------+-----------+--------- Typical cases of gout. | 9·5 | 13 | 1·1 | 230 | 8·4 | 12 | 2·2 | 164 | 7·2 | 17 | 2·4 | 200 | 6·8 | 14 | 1·7 | ---------------------------+-----+-----------+-----------+--------- Typical early interstitial | 9·5 | 25 | 2·5 | 185 nephritis. | 8·0 | 37 | 2·7 | 150 | 5·0 | 37 | 3·9 | 130 | 7·1 | 16 | 2·0 | | 6·6 | 24 | 3·3 | 185 | 6·3 | 18 | 2·1 | | 8·7 | 20 | 3·6 | 100 | 7·0 | 33 | 2·6 | 117 | 6·3 | 31 | 2·1 | | 6·3 | 23 | 2·4 | 150 ---------------------------+-----+-----------+-----------+--------- Chronic diffuse and | 8·0 | 80 | 4·8 | 240 chronic interstitial | 4·9 | 17 | 2·9 | 170 nephritis. | 8·3 | 72 | 3·2 | 238 | 5·3 | 21 | 1·9 | 145 | 9·5 | 44 | 3·5 | 210 | 2·5 | 19 | 1·9 | 120 | 7·7 | 67 | 3·1 | | 6·7 | 17 | 1·6 | 165 | 8·3 | 39 | 2·9 | | 6·5 | 24 | 3·0 | 200 ---------------------------+-----+-----------+-----------+--------- Typical fatal chronic |22·4 | 236 | 16·7 | 210 interstitial nephritis. |15·0 | 240 | 20·5 | 225 |14·3 | 263 | 22·2 | 220 |13·0 | 90 | 11·1 | 265 | 8·7 | 144 | 11·0 | 225 ---------------------------+-----+-----------+-----------+---------

(Myers and Fine: “Arch. Int. Med.,” 1916.)

The salient feature of the table is, however, the fact that in early interstitial nephritis the retention of uric acid precedes that of urea or creatinine.

Its importance resides in the reflection that it lends support to those who contend that renal change, leading to failure of excretion of uric acid, is the primary cause of gout; in other words, it gives colour to Magnus Levy’s contention that the phenomena of gout are referable to “a deficient and restricted secretory power of the kidney.” The existence of such a selective excretory incapacity, i.e., for uric acid, does not, he considers, predicate a genuine nephritis. He maintains that such disability on the part of the kidney for uric acid excretion may exist without morphological change; in other words, he thinks it conceivable that a single function of the kidney can become almost exclusively insufficient, though later real damage to the organ and a nephritis frequently follow.

Reflecting on the above theory, it is obvious that, if carried to its logical conclusion, it would appear to postulate that gout is nothing more than a form of renal disorder, marked simply by functional inability to excrete uric acid. The postulate is no mean one, for, as Sir Archibald Garrod says, “If the fault is in the kidneys alone, gout must be removed once and for all from the category of metabolic disorders, and placed among the sequelæ of renal inadequacy, at least in so far as the uric acid phenomena of the disease are concerned.”

Furthermore, Levy’s hypothesis involves the assumption that the excreting functions of the kidney for uric acid and urea are separate and independent of each other, and to discussion of this we now pass on.

THE RELATIONSHIP, IF ANY, BETWEEN THE AMOUNTS OF URIC ACID AND OF UREA, AND TOTAL NON-PROTEIN NITROGEN IN HUMAN BLOOD

Taking samples of human blood from (1) unselected insane subjects and (2) chronic nephritics, Folin and Denis determined the amounts therein of urea, total non-protein nitrogen, and uric acid. The figures obtained showed that “there is apparently no relationship between the amount of uric acid and the amount of urea or total non-protein in nitrogen, in human blood.”

That such a discrepancy should obtain is doubtless of profound though as yet imperfectly grasped significance. These authorities rightly assume that, since the kidney is practically the sole avenue for nitrogenous waste excretion, it follows that the urea and total non-protein nitrogen of the blood must in the main be inversely proportional to the general efficiency of the renal organs. Then, obviously, the same law, too, should, in lack of some other plausible explanation, govern the excretion of uric acid also. But, as the above generalisation portends, it is apparently not so.

Fortunately, Folin and Denis prosecuted their study still further, taking in examples of gout (with and without clinically recognisable nephritis), also instances of leukæmia and lead poisoning.

The blood, again, in these disorders betrayed the same peculiarity, viz., that while containing an excess of uric acid, it did not contain correspondingly large amounts of urea or other waste nitrogen; in other words, the findings in the blood in gout were in full accord with the above generalisation, i.e., the apparent lack of any relationship between the amount of uric acid and that of urea or total non-protein nitrogen in the blood.

Now in leukæmia the cause of the uricæmia is over-production of uric acid, but in this instance the same is correlated with an increased elimination of uric acid by the kidneys.

Turning to lead poisoning, the medicinal administration of lead acetate results in a great diminution of uric acid excretion, a response consistent with the view that lead inhibits the excretory power of the kidney for uric acid, the change, at first functional, becoming later organic; for it is held that the uricæmia, associated with plumbism, proves that the action of the lead is not due to inhibition of the formation of uric acid.

Lastly, as to gout, opinion still wavers as to whether or not the excretion of uric acid in this disorder is appreciably lowered. On the other hand, it is significant that the reverse is never claimed, viz., that in gout the uric acid output is abnormally raised. Now, as we saw in leukæmia, the high uric acid blood content is accompanied by a correspondingly high uric acid output; but, on the contrary, in gout, despite the accumulation of uric acid in the blood, there is no parallel increase in its elimination.

Reflecting on the above considerations, Folin and Denis claim that “the mere fact that the uric acid may accumulate in the blood of the gouty without being accompanied by an increased elimination constitutes definite proof that the gouty kidney is damaged with reference to its ability to eliminate uric acid.”

In all deference, we doubt the legitimacy of the inference, if only for the very excellent reason that, to quote Von Noorden’s words, even to-day “it remains uncertain whether the retention of urate arises because the outlet is blocked, or because the uric acid is held fast by chemical affinities.”

Apart from this, there are several objections to Folin and Denis’ assumption.

URICÆMIA NOT NECESSARILY DUE TO RENAL DEFECT

Thus Pratt, in some examples of his cases of gout, found that there was no apparent diminution or delay in the output of exogenous purin in the urine. On the other hand, he observes that “our study of the blood shows that a marked increase in retention of uric acid in the blood may result from the ingestion of purin bases even when no evidence of retention is found on examination of the urine.” This would appear to indicate that the uricæmia, sequential to exogenous purin intake, ensues independently of and apparently despite the absence of any delay or diminution in uric acid elimination.

Again, Walker Hall, discussing the metabolism of exogenous purins, reminds us that a gouty subject excretes an excess thereof as completely as a normal individual, with only this difference, that he takes a longer time to do so; but even this disability is removed by a simultaneous intake of atophan. His comment is that “the gouty kidney, therefore, is not poisoned beyond compensating for and responding to an extra load.” “Perhaps,” he says, “the situation may be summed up in the observation that the uricæmia of the gouty is maintained in spite of a fair renal elimination.”

URICÆMIA NOT PECULIAR TO NEPHRITIS

Again, a grave obstacle to the acceptance of Folin and Denis’ inference is that uricæmia, though incidental to nephritis, is not peculiar thereto.

Thus Roy Upham and Higley noted its presence in 85·6 per cent. of their cases of nephritis; but, on the other hand, they found that no less than 40 per cent. of another series of clinical cases, not suffering from nephritis, also showed uricæmia.

This would appear to indicate that, while uricæmia is an exceedingly common symptom of early chronic interstitial nephritis, it is by no means specific for that disorder; in other words, its diagnostic valency as a symptom of nephritis is distinctly limited.

Reverting now to gout, what evidence is there that the uricæmia therein is due to defective eliminatory capacity on the part of the kidney for uric acid? Certainly there is no proof that the kidney, at any rate in the initial stages of gout, suffers from this particular functional disability. Indeed, the fact that, at the very acme of an acute attack, the output of uric acid is not only not diminished, but actually increased, constitutes strong proof of the reverse.

Again, as modern investigations show, the variations in the uric acid content of the blood, re the incidence or intensity of attacks, are most erratic. Far from its being essential that uricæmia be present, acute attacks may occur with even a sub-normal uric acid blood content; in short, the variations are so erratic as to seem quite out of keeping with the assumption that the uricæmia in gout is primarily of renal origin.

If it were so, one would expect no such vagaries in the uric acid content of the blood. One would rather, given the existence ab initio of a renal functional defect, look for not only a permanent uricæmia, but further, from time to time, augmentations and diminutions thereof, synchronising with the rise and wane of gouty paroxysms; in other words, that in gout the clinical course and crises of the disorder would be linked up with harmonious variations in the degrees of uricæmia.

URICÆMIA DOES NOT NECESSARILY PORTEND GOUT

If it were so, why does not every case of nephritis develop gout? The researches of Myers and Fine have shown that uric acid is the nitrogenous metabolite that first accumulates in the blood in early interstitial nephritis. Only in its later stages do urea and other waste nitrogenous products undergo like retention therein.

Now let us review these findings, re nephritis, in light of another statement by Folin and Denis, which runs as follows:—

“In pure gout, unaccompanied by any abnormal urea retention in the blood, the kidney is damaged (so far as we yet know) only with its function of removing down to the normal level the uric acid of the blood.”

Is it not clear, then, that in the early stages of nephritis, viz., prior to retention of urea and other waste nitrogen, we have precisely that isolated functional renal disability, i.e., inability to excrete uric acid, that we postulate to be in operation in the initial stages of gout?

Yet, notwithstanding this similitude in the blood content of the two disorders, cases of nephritis do not necessarily develop gout. Indeed, as a matter of fact, examples of nephritis, of all grades and intensities, may run to their full end without manifesting any symptoms even remotely reminiscent of gout. Even Magnus Levy, ardent advocate as he is of the primary renal origin of gout, could not but admit that this salient clinical obstacle barred the way to acceptance of his otherwise plausible view. However, he fails to proffer any other solution of the problem.

To our mind, albeit, the disparity carries with it the inevitable postulate that in gout some other factor intrudes, some tertium quid, something vital, something biological, haply an infection. For even if we grant, for the sake of argument, that renal retention, if it were proved, might explain such anomalies in the excretion of uric acid and other nitrogenous metabolites as occur in gout, yet, nevertheless, no one could possibly contend that this factor alone could explain the nature of gout, could adequately account for its dramatic and protean phenomena.

TO WHAT MAY BE ASCRIBED THE DEFICIENT ELIMINATING CAPACITY OF THE KIDNEY FOR URIC ACID?

Naturally the advocates of the renal theory had to account in some way for the alleged functional disability of the kidney. Thus, Sir Dyce Duckworth, recalling the occasional occurrence in hysteria of anuria, held that, judging from the general phenomena of acute gout, “the influence of the nervous system ... must not be left out of account as a possible determining factor for renal inadequacy.”

Others, with whom Duckworth disagreed, propounded the view that the deposition of urates in the renal tissues was essential for the initiation of a nephritis in the gouty. Duckworth, on the other hand, held that nephritis could develop in their absence.

Croftan considers the renal changes in gout identical with those of chronic plumbism. From experiments with hypodermic injections of xanthine and hypoxanthine over a prolonged period, he concludes that the presence of minute quantities of purin bases in the circulation is capable of producing marked renal changes. On the other hand, uric acid, injected into the circulation of healthy animals for a period of over three months, produced no renal change whatever.

As to this possibility, viz., that the circulating uric acid might lead to nephritis in the gouty, some reflections of Folin and Denis are instructive. Normal blood, according to these observers, contains not less than from 1-2 or 2-5 mg. per 100 grams, while that of gouty blood does not, in their experience, exceed 6 mg. Continuing, they observe, “There is, however, no reason to suppose that a uric acid concentration of 4-6 mg. per 100 grams of blood is very much more irritating or stimulating to the kidney than the somewhat more dilute solution represented by normal blood. Disregarding the insolubility of uric acid, the elevation of its threshold of elimination from 2-4 or 6 mg. (per 100 grams of blood) is certainly a small one. Kidneys in which the threshold of elimination for urea has risen by 10-20 mg. (per 100 grams), or even more, are extraordinarily common.”

While they consider that such urea and total nitrogen retention may possibly bespeak latent or incipient nephritis, they recognise that no appreciable effects on health have as yet been determined in connection therewith. But more pertinently to our point, they make the further pregnant observation, “In the case of uric acid it seems to be purely a matter of insolubility that corresponding or even smaller degrees of kidney insufficiency with slight uric acid accumulation should result in all the serious consequences involved in the development of gout”!

Again, some have attempted to account for the assumed renal incapacity as being part of the tissue peculiarity of the gouty subject. “Without doubt,” says Duckworth, “there are peculiarities of tissue in the gouty, and with this may very possibly be associated peculiarities of tissue function and metabolism.”

Naturally this suggests the further question, Are there any distinctive histological changes in the gouty kidney? On this point Walker Hall has some apposite reflections. Taking Folin’s figures as a basis, it transpires that in acute and chronic nephritis, also in arterio-sclerosis, there is an average content of 2·5 mg. uric acid per 100 grams of blood. Now, notwithstanding the fact that in these conditions an appreciable quantity of the renal tissues is, functionally speaking, temporarily or permanently out of action, nevertheless “the extraction of uric acid from the blood and its subsequent excretion are practically normal.” The inference is that a relatively small moiety of renal tissue suffices for the excretion of the daily quantum of uric acid in the urine.

Now in contrast thereto, the blood content in gout and lead poisoning is about 4·5 mg. uric acid per 100 grams of blood, or “an increase of about 50 mg. in the total blood-stream at any one moment (an increase from the normal 70 up to 120 mg.).” Continuing, Walker Hall observes that “the gouty kidney per se, even when arterio-sclerotic conditions prevail, does not show anything like the amount of cellular damage which occurs in acute or chronic diffuse nephritis.” Thence he argues if histological changes be taken as a criterion of functional efficiency, then the gouty kidney should be more capable of excreting freely than the diffuse nephritic organ.

How does this work out in actual daily life? he asks. “0·5 gram, in a normal adult, represents the average daily endogenous uric acid excretion in the urine, while that of a gouty subject is about 0·45 gram. Now, assuming that the type and extent of the endogenous metabolism is identical in each instance, then the balance, i.e., 0·05 gram, is distributed between the uric acid pent up in the tissues and the uratic deposits, i.e., tophi.” Walker Hall tells us it has been stated that about 0·01 gram suffices to cover the amount deposited as tophi every twenty-four hours. The residual 0·04 gram runs to swell the amount in the blood and lymph-streams. “The increase is 0·0114 to 0·0118 gram per litre of blood; in other words, the actual increase of uric acid circulating through the kidneys is about 0·00047 per hour,” which, as Walker Hall contends, “seems to be a very trifling difference, especially as it is one of amount and not a type.” In other words, it is quantitative, not qualitative. But, trivial as the disparity is, to what may it be referred? To Walker Hall’s mind, if we are to appreciate the standpoint of those who maintain that the gouty uricæmia is referable to renal inadequacy, it is necessary to postulate the presence of a poison acting upon the renal tubules specifically.

In the gouty uric acid excretion is maintained at a “low physiological level to the very end,” and it is easier, he thinks, to adopt the above hypothesis as to its cause than “to conceive of a poison acting upon the nuclear processes in such a way as to induce a persistently low uniform level” of purin excretion.

This view, viz., of a toxin acting specifically upon the uric acid excreting cells of the kidney, seems to be the only reasonable assumption available. But even this is difficult of adherence when we recall the fact that the effect of the toxin is so readily neutralised by a few grains of atophan. Always we have to recollect, too, that under normal conditions, even given a constant diet, the elimination of uric acid displays wide variations. Also the uric acid output in the subjects of chronic gout, when placed on a fixed diet, differs but little from that of normal individuals on a like dietary. At most the excretion but tends to fall to, or slightly below, the lower normal limits of uric acid elimination.

From the foregoing considerations it is but too obvious that those who render obeisance to the primary renal origin of gout have not only yet to prove that the functions of the kidney are defective, but also upon them lies the onus probandi why gouty subjects should exhibit, or acquire, such a disability.

URATIC DEPOSITS IN NEPHRITIS

Here, again, we light upon another point of contact between gout and nephritis, for an interesting feature of the latter disorder is that the retained uric acid, purins, and other excretory products are deposited in cartilage and serous membranes. At these sites they are frequently detected post mortem, though they fail of ante-mortem recognition.

Impressed by the fact that, at post-mortems, uratic incrustation of the articular cartilages was frequently observed in persons who had never suffered from overt gout, Ord and Greenfield sought to ascertain the frequency with which such uratic deposits were associated with renal disease. Out of ninety-six cases presenting renal lesions, no less than eighteen exhibited uratic deposits in the joints.

A still more elaborate research in this sphere was undertaken by Norman Moore. Out of forty-nine cases of chronic interstitial nephritis, uratic deposits were present in twenty-two instances. Again, out of nine cases of chronic parenchymatous nephritis, deposits were found in the joints in two cases. With respect to the first group he observes that “chronic interstitial nephritis is not invariably accompanied by deposits in the articular cartilages, though usually accompanied by traces of degeneration in some of the articular cartilages.”

Levison, too, an ardent supporter of the primary renal origin of gout, noted that all the subjects dying at the Communal Hospital, Copenhagen, of granular kidney disease (during a period of fourteen months) exhibited uratic deposits in one or other of their joints, although they were never known to have had any definite attack of gout.

Luff, in the following table, shows the results of the examination of the joints in seventy-seven cases of granular kidney disease.

-----------------------------+---------------+---------------- | | Uratic deposits | No. of cases. | in joint or | | joints. -----------------------------+---------------+---------------- Known to have had gout | 10 | 10 Never known to have had gout | 67 | 31 | -- | -- Totals | 77 | 41 -----------------------------+---------------+----------------

Of the ten cases known to have suffered from gout, the renal condition was in every instance defined as “markedly granular,” or “fairly granular.” Uratic deposits were invariably present in one or more joints. Of the sixty-seven examples not known to have had gout, uratic articular deposits were found in 46 per cent., which approximates, more or less closely, to Norman Moore’s findings. It is noteworthy that in several of the instances, lacking uratic deposits in the joints, the kidneys were described as “slightly granular,” or “faintly granular.”

-------------------------------+---------------+---------------- | | Uratic deposits | No. of cases. | in joint or | | joints. -------------------------------+---------------+---------------- Marked granular kidney disease | 26 | 20 -------------------------------+---------------+----------------

If of the sixty-seven cases there be selected only those described as “markedly granular,” or “typical granular kidneys,” the incidence of uratic deposits in the joints, as revealed by the second table, reaches no less a figure than 77 per cent.

Another authority, discussing the frequency of incidence of uratic deposits in the joints in cases of chronic interstitial nephritis, states that, at post-mortem, from 50-80 per cent. show their presence—this, moreover, in cases known not to have had gout.

DIFFERENTIATION OF URATIC DEPOSITS IN GOUT AND NEPHRITIS

Uratic deposits, it is true, occur in both these disorders. But it is with a difference. In gout the uratic deposit assumes the form of tophi, whereas in nephritis it is not so. In the latter the uratic deposit is in the nature of a passive deposition—an uratic incrustation of the articular cartilages.

Again, in gout the deposition is sudden and associated with an acute paroxysm; while in nephritis it is gradual and unassociated with inflammatory reaction.

In gout the uratic deposits are overt, manifest as tophi; in nephritis, occult and unrevealed (ante-mortem).

Uratic deposits in the form of tophi occur in gout, in the absence of clinically recognisable interstitial nephritis. But tophi do not occur in nephritis if uncomplicated by gout.

In conclusion, the mere fact that uratic deposits affect such widely disparate forms in these two disorders is to our mind a sure indication that their mode of origin and formation is equally diverse—the one vital, biological; the other passive, mechanical.

CLINICAL ASSOCIATIONS OF GOUT AND GRANULAR KIDNEY

It cannot be denied that gout and granular kidney are frequently met with in close association. But neither can it be disputed that in these disorders, as in many others, their outward affinities do but hark back to inward disparities. The occasional overlapping of the two affections, the trenching of the one upon the clinical or pathological territory of the other, must not blind us to the essential distinctness of the two morbid entities. Doubtless to the earlier advocates of the renal theory their not infrequent co-existence bespoke some hidden nexus, and at least seemed confirmatory of their views as to the pathogeny of gout. But, even if we allow that the connexion between the two disorders seems superficially intimate, it cannot be gainsaid that it is neither constant nor essential. For we have to recollect that—

(1) Some gouty subjects never develop granular kidney.

(2) Some individuals with granular kidney never develop gout.

Also we have to recall that—

(1) Paroxysms of gout often occur for many years before the symptoms of interstitial nephritis develop.

(2) In persons of gouty stock acute attacks may ensue at an age at which nephritis is practically unknown.

Apart from the difficulty of reconciling these disparities, we cannot overlook the fact that both gout and granular kidney are very common diseases, sufficiently common, as Samuel West pointed out, to be not infrequently associated accidentally, without any cause or connection. Again, both affections, be it observed, are prone to develop in the middle and later decades of life. In light of this, is it not readily conceivable that both may arise independently, mere coincidences, both evidences of pre-senilism? Hastings Gilford, indeed, classes gout with syphilis, lead, and alcohol as amongst “the chief promoters of pre-senility.”

Again, certain toxic agents which predispose to or initiate renal mischief also favour apparently the incidence of gout, e.g., lead and alcohol. Samuel West, discussing the relationship of both gout and lead to granular kidney, maintains that, though each may produce chronic change in the kidney, neither of them causes granular kidney. But the presence of granular kidney, he holds, greatly enhances the liability of the victim to gout on the one hand and plumbism on the other; also, to both together and in each affection alike markedly increases the gravity and the risk.

Sir William Roberts, too, has some wholly relevant observations on this point. Thus all will agree with him that “it is difficult to conceive that plumbism induces the same constitutional diathesis as that which obtains in true gout.” He held that gout and plumbism, though they differ in all other respects, yet have one point in common, a tendency to uratic deposition. But such precipitation, he contended, was the outcome of a gouty tendency, reinforced by lead poisoning; or if, on the other hand, uratic deposits occurred in plumbism, the same had but accentuated a pre-existing gouty diathesis. In this connexion, too, it should be recalled that the frequent association of gout and lead poisoning which exists in London is not seen in the North of England or in North America.

Is it not clear, then, that reflection on the broad clinical affinities exhibited by gout and granular kidney does but emphasise the essential distinctness of the two morbid entities? Inferentially, too, it lends no colour to the assumption that gout is of primary renal origin.

That the victim of gout, despite uricæmia and those unequivocal tokens, tophi, may, notwithstanding repeated arthritic outbreaks, be in the intervals in sound if not exuberant health, is a clinical truism. His kidneys, too, may, as far as can be ascertained, be normal; and his blood pressure not beyond what might be expected at his age. His output of uric acid may but touch the lower normal limit or a little less, and his metabolism of purin-rich foods be but a little protracted. Thus he runs his course, more frequently than not a strenuous one, chequered by occasional outbreaks which not seldom he regards as salutary rather than otherwise. Then, sooner or later, in one, two, or even three decades, that Nemesis of age, arterio-sclerosis overtakes him with its correlated chronic nephritic change.

Is not this very reminiscent of what Walker Hall reminds us of, the sequence of events in lead poisoning and alcoholism? “These poisons affect the general metabolism adversely and are connected with disturbances of purin assimilation and output. At a later stage they produce arterio-sclerosis and renal insufficiency.” And as he shrewdly observes, “It is, therefore, of importance to exactly appraise the stage of the disease when interpreting the results of experiments upon gouty individuals. When this obtains widened application, many generally accepted statements will have to be re-written.”

In conclusion, therefore, we see that the weight of clinical evidence is against the primary renal origin of gout, for not only are renal changes frequently slight, but they are often entirely lacking in gout. Confronted with these difficulties, the question inevitably rises as to whether there does not exist a special morbid entity, gout, which develops independently of renal abnormalities?

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XI. URICÆMIA IN GOUT

In the summer of 1848, Garrod made his momentous announcement that “the blood in gout always contains uric acid in the form of urate of soda, which salt can be obtained from it in crystalline state.” Some eleven years later in his classic work on gout, he reiterated his affirmation, but appended thereto the words, “in abnormal quantities.” Garrod’s analyses were mainly qualitative, but, at any rate, in one instance, he obtained from a gouty patient the equivalent of 5 mg. of uric acid per 100 gm. of blood serum, maintaining, however, that this amount was much below that really present.

But not until 1895 was a series of quantitative estimates undertaken when Klemperer in three gouty subjects passing through an attack found the blood content of uric acid to be 6·6 mg., 8·8 mg., and 9·5 mg. per 100 c.c. of blood. Some years later, Magnus Levy, investigating seventeen gouty individuals, found that the amount of uric acid in the blood ranged from 2·1-9·5 mg. per 100 c.c.

Brugsch and Schittenhelm noted that, in gouty victims, uric acid was still present in the blood even when they had been on purin-free diet for weeks or months. They held endogenous uricæmia to be a constant symptom in gout. Even as late as 1913 the former investigator contended that, in a healthy person on a purin-free diet, the presence of uric acid in the blood cannot be satisfactorily demonstrated. But it must be recollected that the precipitation (ammonical silver and cupric bisulphite) method was beset with disadvantages. An approximate estimate only of the blood content of uric acid was with difficulty to be achieved even when large quantities were available.

Fortunately, however, our powers of analysis in this direction became greatly enlarged with the introduction in 1913 of the colorimetric method of Folin and Denis.

FOLIN AND DENIS’S METHOD

This colour reaction is so sensitive that one part of uric acid in a million parts of water can be detected. Moreover, unlike the older methods which required from 75-100 c.c. of blood or more, determinations can be made with 20 c.c., and if the blood be rich in uric acid only 10 c.c. Walker Hall observes that the procedure “has many advantages and does not take up much more time than some of the qualitative methods when once the technical difficulties are overcome.” He described it as follows:—

Twenty cubic centimetres of blood are withdrawn into a wide-mouthed, tared bottle containing 0·1 gramme of finely-powdered potassium oxalate. The flask and contents are then weighed. Five times the weight of n/100 acetic acid is heated to boiling. The oxalated blood is poured into the boiling acetic acid solution, and the heating continued until the solution has begun again to boil. The mixture is filtered hot. The clear filtrate and wash waters are acidified (0·5 c.c. of 50 per cent. acetic acid) and evaporated to 3 c.c. Five drops of a 3 per cent. silver lactate solution, two drops of magnesia mixture, and ten to fifteen drops of strong ammonia hydrate are next added. The mixture is centrifugalised. The supernatant fluid is removed. To the residue five drops of freshly-saturated hydrogen sulphide water and one drop of strong hydrochloric acid are added. The tube is placed in a beaker of boiling water for ten minutes in order to remove the hydrogen sulphide. The supernatant fluid is added to 2 c.c. of a solution containing 100 grams of sodium tungstate and 80 c.c. of 85 per cent. phosphoric acid in 1,000 c.c. of water and 10 c.c. of a saturated sodium carbonate solution. The resultant blue solution is then compared with a standard uric acid solution, and the result obtained by the following formula:—

(20_V_)/(RW) mg. of uric acid per 100 grams blood,[20]

where 20 represents depth in millimetres of standard solution,

R, the depth of unknown solution, V, the volume to which the unknown solution is diluted, W, the weight of blood taken for the determination.

URIC ACID A NORMAL CONSTITUENT OF BLOOD

Up till quite recently it was held that in normal persons the amount of uric acid in the blood was too small to be detected; also that uric acid was not demonstrable in the blood of normal individuals when on a purin-free diet. On the other hand, if the subject’s blood was found to contain uric acid, while on a purin-free diet, it was held a characteristic feature of gout and of prime diagnostic import.

But, since the introduction of Folin and Denis’s method, it has been established that uric acid is constantly present, in demonstrable amounts, in human blood. These authorities, using their colorimetric method, found that the uric acid content of the blood ranged from 0·7-3·7 mg. per 100 grams. They believe that 1-2 mg. of uric acid per 100 grams of blood is well within the normal variations, but “are not prepared to say that they represent the full variations.”

However, before applying their colorimetric method to human subjects, Folin and Denis conducted some researches into the uric acid blood content of a variety of animals, the results of which appear in the following table:—

URIC ACID, TOTAL NON-PROTEIN NITROGEN AND UREA NITROGEN IN BLOOD

(The Figures represent Milligrams per 100 grams of Blood.)

------------------------------------+-----+-----------+--------- |Uric |Non-protein| Urea |acid.| nitrogen. |nitrogen. ------------------------------------+-----+-----------+--------- Rabbit (6 cases) |0·05 | 31 | 13 Sheep (mixed blood) |0·05 | 28 | 13 Pig (mixed blood) |0·05 | 32 | 14 Horse (1 case, anti-toxin animal) |0·05 | 54 | 28 Monkey (1 case, poliomyelitis) |0·05 | 60 | 38 Beef (mixed blood) |0·2 | 24 | 14 Cat (2 cases, diet, liver) |0·2 | 60 | 34 Cat (2 cases, diet, milk and eggs) |0·2 | 67 | 37 Cat (2 cases, diet, rice and cream) |0·2 | 31 | 20 Chicken (6 cases, mixed blood) |4·9 | 32 | 8 Duck (4 cases, mixed blood) |4·8 | 34 | 7 Goose (1 case) |4·8 | 26 | 8 ------------------------------------+-----+-----------+---------

The most striking feature of these findings is the marked contrast between the uric acid blood content of mammals as opposed to avians. In the former the amount is minimal—0·2 mg. or less per 100 grams of blood. On the other hand, in the blood of birds, in whose instance the origin of uric acid is so different, it is present in relatively large amounts. As Folin and Denis observe, the small amounts of urea in the blood of birds, as compared with that of mammals, is also worthy of note.

Reverting now to the findings in human subjects, as observed by Folin and Denis, these have been summarised as follows by Walker Hall:—

URIC ACID, TOTAL NON-PROTEIN NITROGEN AND UREA NITROGEN IN BLOOD

(The Figures represent Milligrams per 100 grams of Blood.)

-----------------------------------+----------+-----------+--------- |Uric acid.|Non-protein| Urea | | nitrogen. |nitrogen. -----------------------------------+----------+-----------+--------- Human, group 1 | 0·8 | 36 | 19 Human, group 2 | 1·5 | 34 | 18 Human, group 3 | 2·8 | 36 | 19 Human, with blood pressures of 160 | 2·9 | 50 | 33 Human, with blood pressures of 200 | 1·2 | 50 | 22 Human, with blood pressures of 220 | 2·7 | 40 | 19 Human, with blood pressures of 260 | 3·9 | 52 | 20 Human, alcoholic | 1·0 | 43 | 29 Human, chronic gout | 3·9 | 25 | 13 Human, chronic gout | 4·4 | 30 | 15 Human, chronic gout | 5·2 | 20 | 13 Human, lead poisoning | 4·7 | 50 | 31 Human, lead poisoning | 4·8 | 52 | 32 Human, leukæmia | 3·1 | 33 | 14 Human, acute nephritis with | | | arterio-sclerosis | 2·7 | 40 | 19 Human, chronic nephritis with | | | arterio-sclerosis | 2·5 | 38 | 19 -----------------------------------+----------+-----------+---------

Interesting and valuable as are the above findings, Folin and Denis are careful to point out that, even as regards the first three groups in the above table, “the figures can scarcely be said to represent the strictly normal variations, for no attempt was made to select physically normal persons.” The samples of blood were drawn from patients newly admitted to the Boston Psychopathic Hospital.

It may be noted that of all the mammals examined the blood of man contains by far the greatest amount of uric acid. Also that in humans the uric acid blood content varies in different persons, and, moreover, as Walker Hall points out, “the figures lend support to the view that there may be groups or families exhibiting similar features.” It will be seen, too, that the blood uric acid in gout and lead poisoning stands at a high level, though not so elevated as was formerly maintained. From the figures, too, it may be gleaned that apparently no relationship obtains between the amount of uric acid and that of the urea or total non-protein nitrogen in the blood.

At the same institution in Boston, Adler and Ragle conducted a similar series of investigations, though on a more extended scale. These observers, taking 156 unselected psychopathic patients, found that in 107 examples the uric acid content of the blood was from 1-2 mg., in thirty-eight more than 2 mg., and in eleven instances less than 1 mg. To sum up, the uric acid content varied from 0·7-4·5 mg. per 100 grams of blood, an average of 1·7 mg.

As before stated, it was until recently maintained that in the blood of normal individuals, on a purin-free diet, uric acid was undemonstrable. But McLester, utilising Folin’s method, found uric acid in the blood of fifteen healthy individuals, who had been on a purin-free diet for at least three days, and this in amounts ranging from 0·5-2·9 mg. per 100 grams of blood, an average of 1·4, as contrasted with 1·7, the average amount in Adler and Ragle’s series. Pratt, discussing these findings, considers that the fact that the average amounts approximate so nearly in the two series is worthy of emphasis. This especially as all McLester’s examples were young healthy adults on a purin-free diet, while the patients studied by Adler and Ragle were of all ages and on a mixed diet.[21]

EFFECT OF EXOGENOUS PURINES

As we are aware, the amount of uric acid excreted in the urine increases markedly on a purin-rich diet. But recent researches appear to raise doubts as to whether the uric acid content of the blood rises correspondingly. Thus, according to Walker Hall, “a state of uricæmia is said to exist if the amount of uric acid in the blood exceeds 0·8 mg. per 100 c.c.” The figure he considers is probably too low for, after an average meat breakfast, the blood uric acid rises to 1 or 2 mg. per 100 c.c. in normal adults, or even higher after an excessive intake of purin-rich foods.

On the other hand, Denis, investigating the effect of ingested purin on the uric acid content of the blood, found that in normal individuals no increase in the circulating uric acid follows the intake; in other words, the kidney, in normal persons, is quite capable of excreting any excess of uric acid presented to it, thereby keeping the uric acid of the blood at the same level as obtains when only the endogenous moiety thereof has to be eliminated.

Moreover, another factor, according to Folin and Denis, that operates in the same direction is the binding capacity of the tissues for uric acid. Pratt of Boston’s observations, too, appear to indicate “That the uric acid derived from exogenous purin does not accumulate in the blood unless there is a disturbance in the uric acid metabolism.”

On the other hand, given damage to the kidney (even when this has not progressed to the point when nitrogen retention is apparent, as shown by the non-protein nitrogen values), an accumulation of uric acid takes place in the blood after a short period of purin feeding.[22]

Now, as to the second regulating factor, the retention capacity of the tissues for uric acid, it may be said that the amount, in normal subjects, would appear to be small. But Fine, it may be noted, found that the uric acid content in divers tissues was relatively proportionate to that of the blood, whether normal or increased in amount.

But, to resume, Denis also demonstrated that the uric acid content of the blood in patients suffering from various chronic diseases other than gout was also not increased on a purin-rich diet. To sum up, the researches of Denis would appear to indicate that:—

(1) In normal subjects no increase in the uric acid content of the blood follows exogenous purin intake.

(2) The uric acid content of the blood in patients suffering from chronic diseases, other than gout or renal disease, is similarly not augmented on a purin-rich diet.

(3) The uric acid content of the blood is increased more or less markedly, after a short period of purin feeding, in the presence of defective renal elimination.

In amplification of the second of the foregoing postulates some observations by Pratt may be quoted. This authority is of opinion that the low amount of uric acid present in the blood of unselected psychiatric patients on a mixed diet (Folin and Denis, Adler and Ragle) shows that a retention of uric acid in the blood in any considerable amount for twenty-four to twenty-eight hours rarely occurs. For, as he informs us, these patients at the Boston Psychopathic Hospital, when on ordinary diet, are eating purin-containing food daily, and they might take as much or more purin during the forty-eight hours preceding the blood analysis as is contained in a single sweetbread meal. Now, as Pratt argues, if the uric acid thus derived accumulated in the blood, the amount found would be considerably greater than that of individuals on a purin-free diet. But, on the contrary, it transpires that the average amount of uric acid found by Adler and Ragle in the blood of patients on an ordinary diet was only 0·3 mg. more than that found by McLester in normal individuals on a purine-free diet. The diagnostic significance of these observations will be better appreciated when we come to discuss the sequential increase of the uric acid content of the blood in gouty subjects after the ingestion of purin-rich substances.

URIC ACID CONTENT OF BLOOD IN GOUT

Taking 1-3 mg. per 100 c.c. as the normal, the uric acid content of the blood, in typical cases of gout, according to MacLeod, rises to nearly 10 mg. Gudzent, from his studies, maintains that the blood, in almost all cases of gout, contains as much or even more mono-sodium urate than it can hold in solution (1-8 mg.), in other words, it is in effect a supersaturated solution of the relatively insoluble lactim urate.

Pratt, working in Folin’s laboratory, investigated a series of cases of gout, selecting only those in which (1) Tophi were found, (2) A history of characteristic attacks of acute gout was obtained, or (3) Typical symptoms developed while under observation.

At the time of examination the average uric acid content, irrespective of the diet or condition, was 3·7 mg. In three patients on ordinary diet, who were seen during attacks, the amounts were 4·5, 4·8 and 5·7 mg. of uric acid. In two other patients, also seen during attacks, and while on a purin-free diet, the uric acid in four estimates ranged from 2·4-5·1 mg., viz., an average of 3·6 mg. None of these patients were taking atophan.

Seven patients, on a mixed diet, and free at the time from symptoms of gout, contained on the average 4·3 mg. of uric acid in their blood.

On the other hand, examination of the blood in six patients on a purin-free diet, at the time manifesting no acute symptoms of gout, revealed an average uric acid content of 3 mg.

From the foregoing considerations it may be deduced that:—

(1) In gout there is a condition not of uricæmia, but of hyper-uricæmia.

(2) That on the average the blood in gouty subjects contains twice as much uric acid as that of non-gouty subjects, as evidenced by comparison of the average uric acid content of the blood in Pratt’s series of gouty cases (4·5 mg.) with Adler and Ragle’s non-gouty examples (1·7 mg.).

(3) In contrast with non-gouty subjects, the uric acid content of the blood in gouty subjects is augmented on a purin-rich diet.

(4) Both in the inter-paroxysmal periods and during attacks the uric acid content of the blood, when on a mixed diet, is higher than when on a purin-free diet.

HYPER-URICÆMIA IN NON-GOUTY ARTHRITIS

Pratt, of Boston, has found that a condition of hyper-uricæmia is sometimes demonstrable in joint disorders other than gouty; but he maintains that the following distinction obtains, viz., that while in gout the hyper-uricæmia is generally constant, in other forms of arthritis it appears to be transient.

He cites a case of infective arthritis, not exhibiting the clinical features of gout, in which the first analysis of the blood by Denis revealed a uric acid content of 7·6 mg.; but on a subsequent examination, seven months later, only 0·8 mg. was found, this, though the patient at the time was on a purin-rich diet. This difference is response to exogenous purins in gouty, as opposed to non-gouty arthritics, is well illustrated in the following table.

According to Walker Hall, the following example illustrates the effect of purin-free as opposed to purin diet on the uric acid blood content in a gouty subject:—

--------------------------------+-------+-------------+------------- | Uric | Non-protein | Urea | acid. | nitrogen. | nitrogen. --------------------------------+-------+-------------+------------- Mgs. per 100 gms. of blood. Gout with purin dietary | 5·5 | 52 | 36 Gout with purin-free food | 3·4 | 40 | 18 --------------------------------+-------+-------------+-------------

GOUTY POLYARTHRITIS (PRATT). ---------------------------+----------+-----------------------+---------- |Milligrams| |Milligrams | of | | of |uric acid | |uric acid | in 100 | | in 100 | gms. of | | gms. of | blood. | | blood. ---------------------------+----------+-----------------------+---------- D. N. Gout. Purin-free | 3·1 |52 hours after eating | 5·8 diet. | | 280 grams haddock | | | roe. | | |3 days after eating | 6·2 | | 300 grams roast beef.| K. Gout. Purin-free diet. | 2·4 |24 hours after eating | 3·0 | | 270 grams roast beef.| H. Gout. Purin-free diet. | 1·7 |3 days after eating | 3·6 | | 150 grams thymus. | P. Gout. Purin-free diet. | 2·1 |3 days after eating | 3·4 | | 160 grams thymus. | J. N. Gout. Purin-free | 2·2 |48 hours after eating | 8·7 diet. | | 190 grams thymus. | | --- | | --- Average | 2·2 | Average | 5·1 ---------------------------+----------+-----------------------+----------

NON-GOUTY POLYARTHRITIS (PRATT). ---------------------------+----------+-----------------------+---------- |Milligrams| |Milligrams | of | | of |uric acid | |uric acid | in 100 | | in 100 | gms. of | | gms. of | blood. | | blood. ---------------------------+----------+-----------------------+---------- McC. Chronic polyarthritis.| 1·7 |24 hours after eating | 2·2 Purin-free diet. | | 100 grams of thymus. | M. Chronic polyarthritis. | 2·0 |24 hours after eating | 1·8 Ordinary diet. | | 225 grams of thymus. | H. Chronic polyarthritis. | 2·9 |47 hours after eating | 2·5 Ordinary diet. | | 190 grams of thymus. | | --- | | --- Average | 2·1 | Average | 2·2 ---------------------------+----------+-----------------------+----------

As Pratt points out, if the figures in the two tables be compared, it will be seen that, prior to the sweetbread meal, the average uric acid content of the blood in the gouty and the non-gouty patients was identical. But twenty-four hours to three days, after the purin intake, the average uric acid content of the blood in the gouty was 5·1 mg., while in the non-gouty subjects it was only 2·2 mg.; in other words, in the five gouty individuals a pronounced hyper-uricæmia was produced from one to three days after a purin meal. On the other hand, in the non-gouty subjects the uric acid content was found to be practically unaltered twenty-four to forty-eight hours after the same purine intake.

It would seem, therefore, that some diagnostic importance may be attached to the hyper-uricæmia that is induced in gouty subjects after exogenous purines, as compared with its non-occurrence in non-gouty subjects.

Another interesting point elicited by Pratt was that in his gouty examples, although, after a purin meal, the uric acid content of the blood rose markedly, yet there was no apparent delay or diminution in the output of exogenous purin in the urine. Thus, in one example, after the intake of 190 grams of thymus gland, the uric acid in the blood, in the first twenty-four hours, rose from 2·2 mg. to 4·4 mg., reaching, on the third day, a maximum of 8·7 mg., which, on the fourth day, sunk to 2·7 mg. Nevertheless, 26·2 per cent. of the ingested purin nitrogen was excreted as uric acid. Now, as pointed out in the preceding chapter, it has been shown by many observers that in gouty subjects the excretion of exogenous purin is diminished and retarded. But Pratt’s study of the blood shows that a marked increase and retention of uric acid in the blood may result from the ingestion of purin bases, even when no evidence of retention is found on the examination of the urine.[23]

The clear inference from this is that it is desirable that our urinary findings in respect of uric acid should be reviewed and controlled in light of blood examinations to the same end.

VARIATIONS IN URIC ACID CONTENT OF BLOOD INDEPENDENTLY OF DIET

Considerable variations in the uric acid content of the blood, according to Pratt, may occur both in gouty and non-gouty subjects, and which cannot be attributed to any purin intake. Such oscillations, moreover, may ensue within a short time. A patient of his, admitted to hospital suffering from a severe attack of gout, was placed upon a purin-free diet. Twenty-four hours afterwards examination revealed only 2·7 mg. of uric acid in his blood. Subsequently, after having had no food containing purins for fifteen days, it contained 5·1 mg.

Marked variations in the uric acid content of the blood may likewise occur in non-gouty subjects. After being on a purin-free diet for two days, a patient of Pratt’s, with recurrent iritis, had 2·2 mg., while a few months after, when on a mixed diet, his blood contained only 0·8 mg.

Again, great oscillations in the blood content of uric acid, independent of diet, are sometimes found in cases of non-gouty arthritis. Thus, in one chronic case of this nature, the blood when first examined contained 7·6 mg. of uric acid, but a few months later, when on a purin-rich diet, only 0·8 mg. were present. In another instance of primary polyarthritis the same was strikingly exhibited. Aged twenty-two years, the subject in October was on ordinary diet. His blood at that period showed 2·7 mg. of uric acid per 100 mg. of blood; in December, on a purin-free diet, 5·0; and in May, on a similar dietary, 1·6 mg.

As to whether in healthy individuals, on a purin-free diet, similar variations in the uric acid content of the blood occur, is not sufficiently ascertained. The solitary example that may be cited is by McLester, who, as a result of four examinations of the blood in a normal person on a purin-free diet, found that its uric acid content was practically constant.

The deductions that may be drawn from the foregoing findings are:—

(1) That in gouty subjects pronounced variations of the uric acid content of the blood may occur which are not attributable to the purin content of the food.

(2) That in non-gouty arthritis similar fluctuations in the blood content of uric acid, irrespective of diet, also occur.

(3) That in normal persons, on a purin-free diet, the blood content of uric acid, as far as is ascertained, does not show such variations.

WHAT RELATION, IF ANY, EXISTS BETWEEN THE URIC ACID CONTENT OF THE BLOOD AND ATTACKS OF GOUT?

If uric acid be causally related to gout, it would seem reasonable to expect that the blood content thereof would stand in some clear relation to the incidence or intensity of attacks.

But, according to Pratt and others, no variations indicative of such a relationship obtain. For, independently of acute attacks, and, moreover, in the absence of any pronounced renal inadequacy, the blood of gouty subjects, even on a purin-free diet, contains, as a rule, 4-9 mg. of uric acid.

More pertinently to our point, in the experience of Daniels and McCrudden, it transpires that, contrary to the usually accepted teaching, typical acute attacks might occur without any variation in the uric acid content of the blood or its excretion.

Nor did their iconoclastic findings cease here, for, mirabile dictu! attacks ensued even when the uric acid blood content was at a sub-normal level; this latter, owing to the victims being at the time on atophan, which increases uric acid elimination. In this connection it is worthy of note that, according to Pratt, the uric acid content of the blood may at times be low, even when atophan has not been taken. In one of his cases, on a purin-free diet, only 1·7 mg. was present, and in another case, on a mixed diet, 1·9 mg.

Daniels and McCrudden, too, note that the uric acid content of the blood in gouty subjects may be persistently lowered, even under the normal average. His, again, has recorded an instance of a gouty subject, with multiple tophi, whose blood did not contain an excess of uric acid. Bloch, also, took 200 c.c. of blood from a man, aged twenty-five, suffering at the time from a typical attack of gout in the big toe; but uricæmia was not present.

Bass and Herzberg injected uric acid into the blood of gouty subjects until its content thereof reached 10 mg. per 100 c.c., this without any joint symptoms supervening. The same observers, aspirating joint fluids in non-gouty subjects, noted that the uric acid content was approximately the same as that of the blood. But, in contradistinction thereto, in two gouty subjects, victims of uræmia, they found in the joint fluids 18·5 and 20·8 mg. of uric acid, while the blood content was only 10 mg. and 8·2 mg.

Furthermore, intravenous injection of uric acid engendered a lesser degree of uricæmia in the gouty—this despite impaired renal excretion. To their mind, therefore, the inference was that the bodily tissues in gout display an enhanced capacity for taking up uric acid.

Lastly, Walker Hall, discussing the question as to whether any relation obtains between the degree of uricæmia and the onset of acute attacks, observes that, “the evidence is more general than specific.” Thus he reminds us that excessive intake of purin food has sometimes been followed by, or associated with, an acute outbreak. Also, that the leucocytic destruction which occurs during acute lobar pneumonia and after the use of X-rays has occasionally coincided with an acute paroxysm. To this, again, must be added the fact that atophan curtails the duration of acute attacks, apparently by exciting an increased uric acid output. Superficially regarded, these facts might appear to be conclusive; but, as Walker Hall states, it must be recalled that overeating, overdrinking, trauma, mental disturbances, atmospheric vicissitudes, and bacterial infections have also preceded acute outbreaks.

To sum up, the main conclusions deducible from the foregoing clinical and experimental findings would appear to be that:—

(1) No constant relation has as yet been established between the uric acid content of the blood and acute attacks of gout.

(2) No variations in the same apparently herald or accompany typical acute paroxysms.

(3) Attacks may occur with a sub-normal uric acid blood content.

(4) The tissues of gouty subjects apparently possess an enhanced binding capacity in respect of uric acid.

(5) Given impaired renal excretion in gouty subjects, the uric acid content of the joint fluid rises markedly, exceeding that of the blood.

DISCUSSION OF THE FOREGOING DATA

While the researches of the past decade have proved distinctly encouraging, yet we must not blind ourselves to the fact that the foregoing findings, and alike our deductions therefrom, are largely provisional; for we stand in grave danger of over-emphasising the significance of the results forthcoming from the investigation of isolated samples of blood from different individuals. The recorded estimates of the uric acid content of the blood in strictly normal persons are all too few, the findings in diseased subjects too conflicting, to warrant dogmatic inferences, wide generalisations. In truth, the problem is by no means as simple as may at first sight appear, and this but a slight digression will suffice to make clear.

The Significance of Uricæmia.—It is generally maintained that the blood content of uric acid in gout is above normal. Yet the excretion of uric acid, save during acute attacks, rests within physiological limits. Again, à propos of our claim that the blood is surcharged therewith, we have the awkward fact, as yet inexplicable on chemical or physico-chemical grounds, that the blood-stream can hold in suspension far more uric acid than has ever yet been met with in gout, according to Bechhold and Ziegler no less than 50 mg. of uric acid per 100 c.c. of blood serum before deposition tends to occur. On the other hand, urates are less soluble therein, not exceeding 2·5 mg. per 100 c.c. How remote from the limit of saturation the highest figures observed in gout! What a large margin of solubility is still available!

Again, the uric acid blood content in gout is far less than was formerly thought. Only by a few milligrams does it transcend that found in normal individuals. Can this slight disparity have such profound potentialities as to determine the incidence or not of gout? and this with the saturation point still so remote. The urates, too, being practically non-toxic, how difficult to conceive that the almost trivial excess of the uric acid blood content over the normal is adequate to produce the fulminant and dramatic phenomena of acute gout.

Again, though we speak of uricæmia as a dominant characteristic of gout, we are uncertain whether the alleged increase in the uric acid content of the blood is real or merely apparent. We can, it is true, extract uric acid and urates from the blood-stream, but it does not necessarily follow that it is as such that they circulate in vivo. We need walk circumspectly here for, despite the most modern methods of blood analysis, we are still ignorant as to the exact form in which uric acid exists in the blood-stream; whether the purins of the food appear in the blood-stream as sodium monourate, or in organic fusion. Accordingly, in the interests of progress, it were well to bear in mind the pitfalls that beset uric acid estimation, the insufficiently eclectic capacity of even the most modern tests, and to consideration of these more chastening aspects we now proceed.

Sources of Fallacy in Uric Acid Estimation.—With Folin’s findings as his basis, Walker Hall estimates that, excluding the lymphatics and lymph spaces, the entire blood-stream contains normally 70 mg. of uric acid, i.e., 2 mg. of uric acid per 100 grams of blood, 3,500 c.c. (total quantity of blood).

Thence he argues that, inasmuch as about 1 litre of blood traverses the kidney per minute, the total content thereof of uric acid would gain access to the renal organs in three and a half minutes. Now the average total output of the kidneys is 500 mg. per twenty-four hours. Accordingly, assuming that the blood arriving at the kidneys contains as a constant the above 70 mg. uric acid, the total daily output would pass through these organs in twenty-five minutes.

Now, given immediate extraction of all the uric acid by the renal cells, then the blood in the renal veins will become free of uric acid. If so, the estimates of the uric acid content of the blood will reflect exactly the measure of the endogenous or exogenous nuclein metabolism. But, “if the renal vein blood is not purin-free, then the estimations will fail to yield a true picture of the activities of nuclein exchange.”

Again, as to the precise import of isolated estimates of the uric acid blood content, we must recollect that the excretion of purins is not distributed evenly over the twenty-four hours, varying as it does under the influence of food, exercise, sleep, and other factors. A propos of this, Pratt’s observations clearly show that both in gouty and non-gouty subjects fluctuations in the uric acid blood content also occur, and this independently of diet. To what, then, may these variations be referred? Obviously a question of great moment, especially when we recall the eccentric behaviour of the blood uric acid in relation to the incidence of acute gouty attacks. For, until the inward meaning of these vagaries is revealed, the value of recorded estimates must necessarily be discounted considerably.

We must recall, too, that a certain moiety of the purins derived from nuclein metabolism lags in the lymph spaces and lymphatics, and this, as Walker Hall reminds us, must reduce the quantity present in the blood-stream at any one time. Also, as the same authority reflects, the lymph stream being probably richer in sodium ions than the blood, the entry of the nucleins therein may be retarded and so lead to a still further reduction of the blood content.

There is yet another possibility, he reminds us, viz., “that the purin content of the blood varies in the peripheral pulmonary hepatic and osseous streams, and that, while in some parts the purins are being carried to the kidneys for excretion, in others they are being transported from one organ to another for further metabolism.”

For, as before pointed out, the enzymes responsible for the ultimate disruption of the nucleosides are scattered in different organs, and Walker Hall suggests that “a transport of half metabolised nucleotides from one organ to another may form a part of the normal processes of nuclein metabolism.” This may well lead us on to consider the limitations that beset even the most modern tests in use for uric acid determination.

Disabilities of Modern Tests.—With all its outstanding advantages, even the Folin method of uric acid estimation has its drawbacks. As Curtman and Lehrman have pointed out, different workers have, even on identical blood samples, arrived at results which vary widely. Nor, disconcerting though it be, do the limitations of this mode of hæmo-analysis cease here.

Thus we know from Gudzent and Apolant that the soluble but unstable biurate is constantly being transmuted into an insoluble stable type, in other words, metamorphosis from one isomer into another. But, unhappily, the tests to hand fail of differentiation of the several tautomeric forms of uric acid. Also, as isomers of uric acid actually exist, then quâ Walker Hall, why not isomers of purins and pyrimidins also? But here again our tests are insufficiently eclectic. They give us no clue as to the affinities or blends of purins or pyrimidins for or with other substances.

Again, as our criteria fall short of identifying the exact form of the “purin combinations” it follows, therefore, that they tell us nothing as to whether “the increase is due to a more active transport of purins from one organ to another for further metabolism or simply to a transport to the kidneys for elimination.”

In other words, hampered by the above disabilities in our tests, it is beyond our power to determine whether “the increases denote a supernormal nuclein metabolism or an unusual type of nuclein cleavage.” Should it ultimately transpire that the increase in the purin blood content is a real one, viz., made up of “an excess of normally formed and normally bound purins,” a great step forward will have been achieved. For, to account for the same it will, as Walker Hall observed, be necessary to postulate a supernormal nuclear activity of generalised or localised distribution.

Need for Further Investigations.—While none can doubt that, by means of chemical investigation of the blood, the clinical problem of gout will be elucidated to a much greater extent than has been possible by means of urine analysis, still much remains to be done before recent findings can be applied to the solution of the etiology of gout.

The results of blood analyses up to now have afforded us no clue as to the intimate nature of the warp in nuclein metabolism. At the most, the researches in this sphere do but make it increasingly clear that uricæmia is not the cause but the result of gout.

Albeit, this conclusion does not justify us in putting out of court all thought of uric acid in connection with gout. Any tendency thereto will be immediately checked when we recall that uratic deposits, i.e., tophi constitute the solitary unequivocal token of gout, and to this aspect of the question the ensuing chapter will be devoted.

Meanwhile, systematic investigations of the purin content of the blood, not only in gouty but in normal subjects, would surely dissipate much of the obscurity that envelops this complex question. It were well, too, that blood and urine analyses go hand in hand in our investigations. How illumining these have been in connection with atophan, the increased urinary output of uric acid having been found to be correlated with a simultaneous sinking in the level of the uric acid of the blood.

Again, the excretion of urinary purin ebbs and flows with the intake of food and the degree of muscular activity, while sleep also exerts an influence, not to mention constitutional disturbances, e.g., fever infections, etc.

Can it be doubted that the blood content of uric acid varies with these same vicissitudes? Walker Hall tells us that the data to hand, “as to the rapidity of the appearance of purins in the blood-stream after food, infections, fever, etc.,” though few in number, yet suggest that “the excretion by the kidney is tidal in character, and that the blood uric acid has similar characteristics.” In light of these possibilities, we may well pause before attempting to appraise exactly the significance of isolated blood examinations.

What, too, as the above authority observes, of the influence on the gouty uricæmia of infancy, puberty, the menopause, and for that matter the pre-senile and senile periods of life with their associated vascular lesions? The researches of Uffenheimer prove that even in young children the disorders of purin metabolism distinctive of gout are to be met with, i.e., “infantile gout.”

We stand also in urgent need of knowledge as to the uric acid blood content in the early as opposed to the late stages of gout; in need, too, of further examinations of the blood to this end, not only during the passage of acute attacks, but even more under those conditions which are presumed to determine their incidence.

But, despite these gaps in knowledge, these disabilities of technique, there is no need for despair. “It is a slow progress along the zigzag which leads to the centre of the ‘gouty maze,’ but the researches of the last decade have opened up many new and possible pathways thereto.”

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