Analysis of the urine

Front matter

vV ^

A -r.

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CHAPTER I. Histology of the Urinary Organs

1. The Kidneys .

Urinary Tubules Blood-vessels of the Kidneys Nerves of the Kidney .

2. The Excretory Ducts

Ureters, Kidney-pelvis, and Calices Urinary Bladder .

Male Urethra .

Female Urethra .

PAGE

, 13

CHAPTER III. The Urine

A. A General Description .

B. Physical Characteristics

1. Amount

3. Solid Ingredients .

4. Consistence

5. Color

6. Transparency and Fluorescence

7. Odor

8. Reaction

C. Chemical Composition .

a. Normal Organic Constituents

1. Urea .

3. Coloring Matters

TABLE OF CONTENTS.

a. Urobiline . £. Urine-Indican . 4 Other Normal Organic Constituents

b. Normal Inorganic Constituents .

1. Chlorides

2. Phosphates .

0. Earthy Phosphates /B. Alkali Phosphates

3. Sulphates

c. Abnormal Constituents .

1. Albumen .

Nitric Acid Tesl .

Boiling Test . [a.] Peptone Potasseo-mercuric Iodide Test, for Picric Acid Test, for Sodium, Tungstate Test, for Potassium Ferroeyanide Test, for Metaphosphoric Acid Test, for

Heller's Test .

Mulder's Test.

Oliver's Test Papers .

Trommer's Test .

Robert's Test .

Bottger's Test

Picric Acid Test

Vogel's Method of Approximative Determination

Inosite

3. Leucine and Tyrosine

4. Abnormal Coloring Matters

a. Uroerythrine

£. Vegetable Coloring Matters

7. Blood Coloring Matters

8. Biliary Coloring Matters .

5. The Bile Acids

6. Carbonate of Ammonium

7. Sulphuretted Hydrogen

8. Accidental Constituents The Sediment .

Urine Fermentation Classification of the Sediment

a. The Unorganized Sediment

1. Urates .

2. Urate of Ammonium

3. Uric Acid 4 Calcium Oxalate .

TABLE OF CONTENTS.

PAGE

5. Cystine ....

6. Leucine and Tyrosine

. 158

7. Fat

8. Earthy Phosphates

9. Magnesium Phosphates

10. Triple Phosphates ....

11. Calcium Carbonate b. The Organized Sediment

. 165

2. Epithelium . .

. 167

3. Pus-corpuscles (Donne's Test)

4. Blood-corpuscles ....

., 171

5. Cylinders . .

. 179

7. Spermatozoa ....

8. Cancer Elements ....

. 184

9. Entozoa ....

Addenda.

Concretions .......

. 189

Analysis of the Concretions ....

CHAPTER IV. Reagents and Apparatus for the Approximative Determination of

the Urine Constituents . . . . . .197

Chapter V

Quantitative Determination of a few of the Constituents of Urine ......

I. Estimation of the Degree of Acidity . II. Estimation of the Solid Matters .

III. Estimation of Urea ....

1. Liebig's Method

2. Bunsen's Method

3. Knop-Hufner's Method

IV. Determination of Uric Acid .

V. Determination of Creatinine

VI. Determination of the Total Amount of Nitrogen VII. Determination of Albumen VIII. Determination of Sugar

1. Fehling's Method .'.",'„

2. Knapp's Method

THE

TABLE OF CONTENTS,

IX. Determination of Chlorine X. Determination of Phosphoric Acid . XI. Determination of Sulphuric Acid

CHAPTER VI Key to the Approximative Analysis of the Urine Chemical Investigation

A. Nitric Acid ....

B. Heat Test

C. Test for the Normal Coloring Matters of the Urine

D. Test for the Normal Inorganic Salts of the Urine

E. Further Tests for Abnormal Matters

F. Investigation of the Sediment .

PAGE

219 221 223

224 224 224 225

227 227 227

CHAPTER VIII. Diagnosis of the Diseases of the Urinary Apparatus . . 241

A. True Albuminuria ....... 242

1. Hyperseinia of the Kidney ..... 242

2. Parenchymatous Nephritis ...... 245

a. Acute Parenchymatous Nephritis .... 245

o. Catarrh of the Urinary Tubules, or Desquamative Nephritis ... .... 246

j8. Acute Parenchymatous Nephritis proper . . 247

b. Chronic Parenchymatous Nephritis .... 249

3. Interstitial Nephritis ...... 251

a. Hyperplastic Interstitial Nephritis — Cirrhosis of the Kid-

ney — Genuine Kidney Atrophy .... 252

b. Suppurative Interstitial Nephritis .... 253

4. Amyloid Kidney . . . . . . . 255

B. Forms of Mixed Albuminuria ..... 258

1. Pyelitis 258

a. Acute Pyelitis . . . . . . 259

b. Chronic Pyelitis . . . . . . .261

c. Pyelitis Calculosa ...... 262

d. Pyelitis Tuberculosa ...... 265

3. Cysto-Pyelitis and Pyelo-Cystitis . . . . .279

C. Forms of False Albuminuria ...... 280

1. Cystitis— Bladder-Catarrh . . . . . .281

2. New Growths in the Bladder ..... 288

3. Bladder-Stone 297

4. Diseases of the Urethra and Prostate .... 298 Description of Ultzmann's Saccharimeter ..... 301

ANALYSIS OF THE URINE.

INTRODUCTION.

The results of the generally complicated chemical processes upon which depends the basis of animal life are, on the one hand, the building up of the body, and on the other the breaking down of the same, both included in the common term " regressive (?) tissue metamorphosis." The used-up material — i. e., that which has lost its value to the animal economy — becomes eliminated by the skin and lungs (chiefly in gas form), and by the intestines and kidneys (in solid or liquid form).

In order to have a perfect conception at various times of the nutrition and state of the body (including the normal or pathologically changed material), the greatest possible care must be exercised in the investigation of the excretory ducts themselves, their precise function, and the nature of the material eliminated by them.

In order that the physician may obtain an adequate idea of the changes which take place in the organs of the body, it is important to observe carefully that most important secretion of the same, the urine.

The urine indicates, at least very nearly, by its qualitative and quantitative changes, the variation in tissue life. It offers in addition the advantage of easy collection, and its analysis, so far as it interests the practicing physician, can be made with simple apparatus. The kidney, inasmuch as it is subjected to disease, is not a lifeless filtering machine. Through its pathological processes material is added to the urine, from the presence of which alone is the physician able to make a diagnosis. The urine offers also in general an indication as to the condition of the entire body (including its constitutional diseases), and in particular concerning the secretory and excretory urinary apparatus. On account of the peculiarities of the numerous substances excreted by the kidneys, the urine possesses a great interest for the physiologist and chemist, and under certain circumstances for the medico-legal expert.

The endeavor to diagnose disease from observation of the urine extends back to the remotest period of medical research. The changes of the urine did not escape Hippocrates in his close investigation of diseases. He taught his scholars, under his personal supervision, the symptomatic and prognostical signification of changes in the urine, so far as the then existing state of the other sciences permitted. He directed attention to the external characteristics of the urine, its abnormal amount, color, and clearness, its cloudy or muddy appearance, and the visible differences of the sediment ;

and he referred these indications to diseases of the urinary organs. However arbitrary his explanations of the appearances may be, his observations are for the most part correct. He even endeavored to demonstrate the influence of various foods and drinks on the constitution of the urine. We find also in the descriptions of diseases by Grecian writers the character of the urine considered according to his methods, without departing materially from the views of the great Coic physician. Since Galen more sharply defined and systematized the teachings of Hippocrates, they have prevailed as incontestable truths. For a long time after Hippocrates the investigations on the urine made no progress. Through the following century one finds but an occasional writer who added anything by his own investigations to these transmitted treasures.

To the Arabian Ibn Sina (980-1037), usually known as Avicenna, belongs the merit of having called attention to the fact that different external circumstances, as fasting, wakefulness, over-exertion, and strong emotions, have an influence upon the character of the urine. He proved also that absorbed medicines which are excreted by the kidneys would cause an accidental coloring of the urine. By his successors in the Arabian school nothing of importance was added, although, particularly in the East, each court had an examiner of urine (uroscopen). The most important writer on this subject in the ancient and middle ages is without doubt Johannes, surnamed Actuarius, who lived in the thirteenth century at the Byzantine Court. Uniting his experiences with the observations of the H^pocratic-Galenic schools, he treated in his seven- volumed work " irepl ovpav" in the minntest detail, the physiological and pathological changes of the mine. He gives even a description of the best methods of observation. In this he excels becanse of his clearly detailed demonstration. This work, in which nearly everything was exhausted which could be accomplished by the then existing methods, found in succeeding time so little emulation that this part of aetiology more and more declined. How far the interpretation of changes in the urine had advanced is most clearly demonstrated by the circumstance that it ihirnished material for the satirical representations of the Dutch school of genre painting, as well as for many comedies of Moliere and other poets.

As they had most defective ideas as regards the chemical composition of mine, it was possible for the old observers to take into consideration only its physical properties. We can expect time progress only when chemistry and its methods of investigation have undergone marked development. This decided advance dates from the time of Lorenzo Bellini of Florence (1643- 1704). Bellini evaporated the urine, and observed that by the gradual addition of water the residue was again dissolved, and the solution gradually brought back to its original condition, through different degrees of color and taste. He concluded thereupon that the variation of color and taste depended upon the ratio of the contained water to the solid constituents — a conclusion upon which even now Vogel's color scale is based.

Now important chemical discoveries followed quickly upon one another. Willis discovered sugar in the urine. Brandt discovered phosphorus, the origin of which MarkgrafF attributed to the contained phosphates. Rouelle the younger discovered urea in 1773, and found that in the urine of herbivora were contained carbonate of calcium and a substance, hippuric acid, related to flowers of benzole. In the year 1770 Cotugno found albumen in the urine ; in 1798 Cruikshank declared the relation of this condition to dropsy; and in 1827 Bright proved the connection between kidney disease and albuminuria. At the same time attention was turned to the chemical analysis of gravel and calculi. Among the numerous deserving works on this subject are those of Scheele, Wollaston, Wetzlar, and Prout.

The present advanced state of uroscopy is due chiefly to the labors of twx> Frenchmen. Rayer's researches, which are included in his great work "Les maladies des reins" (1837-41), laid the foundation of our present knowledge of kidney diseases. Becquerel, the son of the renowned physicist, had busied himself for a long time with urine analysis under Andral's direction, to w^hom he modestly assigns the credit of stimulating him to his investigations. He published the results of years of observation in his work " Semiotiquc des urines" (1841). Through the thirty years which followed the publication of that book many observers turned their attention to this subject, so that no other part of organic chemistry possesses so full a literature as this.

After this short sketch of the development of our subject, it only remains to describe in a few words the arrangement of the matter which is here offered. After a cursory account of the microscopical construction and the function of the urinary apparatus, without a knowledge of which an understanding of its pathology is impossible, the physical properties and the chemical constituents of the urine will be separately treated, at least so far as is important for the practicing physician. A description of the microscopical part, viz., the sediment, will then be added. The many repetitions which occur are suitable rather than blameworthy for the beginner.

It is to be hoped that the short table for the method of investigation will not be useless to the beginner. The conclusion is formed of a compendium of the simple uncomplicated diseases of the urinary apparatus, as far as the indications form valuable signs for their diagnosis.

Chapter I

HISTOLOGY OF THE URINARY ORGANS. 1. THE KIDNEYS.*

If one cuts through the kidney from the papilla to the fibrous capsule, it is possible to clearly discern with the unaided eye a concentric arrangement of layers, i. e., the striated medulla and the more granular cortex surrounding the same.

If the blood and urinary vessels have previously been treated with different-colored injection fluids, it is possible to distinguish further subdivisions on the cut surface.

In the papillae and close upon the same the kidney, by injection of the urine-tubes, shows striations ; this portion is known as the papillary part of the medulla. Above this comes a section which is also striated ; but the striations alternate with those filled with the colored injection fluid of the blood-vessels ; this is known as the boundary or limiting layer of the medulla. The third and outermost layer surrounding the others is called the cortical layer.

* The investigations of Kolliker, Schweigger-Seidel, and Ludwig, serve as the basis for this description of histological relations.

ANALYSIS OB THE URINE.

By the colored injection fluids we distinguish the two component parts of the cortex. One of these is striated, and contains the injection fluid of the uriniferous tubes, which striations are the direct continuations of the straight tubes of the medulla, and are called medullary rays (Markstrahlen), or the prolongations of

Fig. 1. — Plane section through the kidney of a dog: the urine- and blood-vessels injected, p, papillary part, and g, boundary or limiting layer of the medulla ; r, cortex. The dark striations of the medulla, h, are bundles of urine-tubes. The continuations of the same into the cortex are the medullary rays, m. The light spaces of the medullary portion, b, correspond to the fasciculi of blood-vessels in the medulla. The light spaces of the cortex studded with dots (glomeruli), c, represent the situation of the labyrinth.

the pyramids ; the other part shows principally small round bodies (glomeruli), colored by the injection of the blood-vessels, and is the so-called labyrinth of the kidney, or, in a narrower sense, the cortex.

In support of this, with the microscope we find the papillary part to be made up of straight tubes; the boundary, partly of straight tubes and partly of straight

HISTOLOGY OF THE URINARY ORGANS. 21

blood-vessels ; the medullary rays, principally of straight urine-tubes ; and finally the labyrinth, partly of looped urine-tubules, and partly of tortuous blood-vessels.

This system of blood-vessels and urine-tubes is supported by a meagre stroma, denser in the medulla than in the cortex. On the external surface of the kidney this substance becomes a delicate membrane, which is loosely adherent to the fibrous capsule. The capsule is composed of ordinary connective tissue, with numerous fine elastic fibres. It envelops the whole organ, is inserted in the hilus, and, surrounding the blood-vessels, sends prolongations to the pelvis of the kidney.

The urinary tubules have their origin in the labyrinth. Each begins there with a spherical dilatation (capsula Malpighii), and " continues as a narrow neck, opening to a wider tube, which, after many windings, runs toward the medulla. When, as a wide, convoluted tube, it has reached the boundary, it suddenly becomes of less calibre, and as a narrow canal penetrates more or less deeply into the medulla; here the descending straight tube turns on itself, forming a narrow loop (Henle's loop), and runs directly upward toward and into the cortex. On reaching the cortex the canal does not seek the place of its origin, but avoids it and runs alongside the nearest medullary ray. Sooner or later it loses its straight direction, and with several convolutions passes as a widened tube (tubulus contortus) among the curved canals of the labyrinth. From there it turns and enters one of the tubes of a medullary ray (Bellini's tubes), the convexity of its curve directed toward the

ANALYSIS OF TEE URINE.

surface of the kidney, thus losing its independent course. The latter occurs as follows : Several canals run from different directions to the same place and become blended

Fig. 2. — p, Papilla, g, Boundary, r, Cortex. I, Capsula glomeruli. II, Convoluted portion of tubule passing into III, descending branch of Henle's loop, h, Henle's loop. IV, Ascending branch of Henle's loop. V, Convoluted portion of tubule joining VI, tubulus Bellinianus. VII, Another tubulus Bellinianus. VIII, Common duct. IX, Ductus papillaris.

into a straight wide tube " (tubulus Bellinianus, Fig. 2) : this runs a direct course until it reaches the papillary part of the medulla, where it unites with a neighboring

* The quotations are from C Ludwig. See Strieker's " Handbook of Histology."

HISTOLOGY OF TEE URINARY ORGANS. 23

tube and so continues (Fig. 2, VIII.) until the united tubes, as the so-called ductus papillaris, empty into one of the calices.

The wall of the capsula Malpighii is made up of a mosaic of cells. The glomerulus is not directly surrounded by the fluid contents of the capsule, this being prevented by a layer of nucleated cells not easily defined, which covers the bunch of blood-vessels. " Beginning at the neck of the capsule, and extending as far as the commencement of the ductus papillaris, the canal wall consists of a tunica propria, lined on the inner surface with epithelial cells." The tunica propria is a homogeneous, vitreous, and elastic membrane.

The epithelium which lines the basement membrane is a single layer of nucleated cells. The form of the nuclei is always the same, round, sharply defined, and showing numerous granules. The body of the cell, on the contrary, varies much as regards form.

In the convoluted tubes the epithelium forms a continuous, jelly-like, opaque mass, with imbedded nuclei. A division of this mass into cells corresponding to the number of nuclei seems impossible. " This epithelial pulp lies only lightly upon the basement membrane ; so that by making cross-sections of the tube the mass can be readily drawn out in a cylindrical form. Microscopically, fat-globules and other dark granules can be seen in this pulp, which is cleared up by addition of dilute acid. Often after the clearing up by acids isolated nuclei appear. In the small canals which form the arms of Henle's loops appears a thin and transparent lining epithelium, the cells of which by their nuclei are brought into clear relief."

On the other side of Henle's loops, where the diameter of the tubes becomes greater, the epithelium presents the appearance of true cylindrical cells, which are laid over one another as shingles, in a direction from the medulla to the cortex. In the tubuli contorti we find again the same jelly-like arrangement as in the curved tubes leaving the capsulse Malpighii. In the straight tubes, even to the ductus papillaris, the epithelium is built up of a single layer of sharply defined cylindrical cells, with their broad bases toward the canal wall and their blunt points toward the lumen. (PI. I., Fig. A, 1.)

The Blood-vessels of the Kldkeys. — The arteria renalis sends the greater part of the blood through the cortex. Its branches penetrate without forming meshes to the limit of the cortex, and here breaks up suddenly into very fine arteries, the arteriole interlobulares and arteriole rectse.

The wrterioloz interlobulares run between every two medullary rays. Having reached the layer of convoluted tubules, they give off a small branch to each capsula Malpighii. This little branch (vas afferens glomeruli} pierces through the ball-like termination of the urinary canal (according to others, it only presses in), and breaks up here " into a free waving bunch of capillaries (glomeruli), which unite again within the capsule to form a common venous stem, the vas efferens glomeruli." This stem leaves the capsule in the same place

HISTOLOGY OF THE URINARY ORGANS. 25

that the vas afferens enters. After the vas efferens leaves the capsule, "it takes its direction toward its own medullary ray, or when this is wanting (as in the outermost layer of the cortex), at once toward the convoluted tubes, where it breaks up into a number of capillaries, forming a network of anastomosing meshes around the tubules." The vasa efferentia communicate by means of capillaries with one another throughout the cortex, and also with the vessels of the medulla, in the same manner,

The arterioles rectw, which go from the cortex into the medulla, have their course in the slit-like spaces which lie in the limits of the medulla between the bundles of urinary tubules, and run to the papillae, in the mean time dividing up into several parallel branches. When these vessels meet the converging bundles of the urinary canals, they break up into capillaries surrounding the urinary tubes, and then are distributed to the surfaces of the papillae. This network of capillaries communicates with that of the cortex.

From the above-described capillary nets the venous stems arise. In the cortex of the kidney, especially in that layer external to the glomeruli, the union of venous stems is star-shaped (venae stellatse). The common venous stem penetrates that part of the cortex endowed with glomeruli and medullary rays, lies alongside of an arteria interlobularis, and receives numerous branches from the cortical network.

The venulce rectee run in the same clefts with the arteries, and on the border of the medulla unite with

26 ANALYSIS OF THE URIKE.

the veins coining from the cortex to form greater stems. The capsnle receives its vessels partly from the arteria? interlobulares, and partly from other arterial stems in the neighborhood, viz., the arteria phrenica, lnmbalis, and supra-renalis. Their capillaries ran partly into the venae steilataB of the cortex and partly into the veins corresponding to the above-mentioned arteries.

The Nerves of the kidney are supplied by the plexus cceliacus of the sympathetic. Their terminations in the kidney are unknown. They ran alongside the great blood-vessels in the same manner as the lymph-vessels which empty into the glands of the groin.

2. THE EXCEETOEY DUCTS.

The ureters, pelvis, and cal ices have an external iibrous coat, a layer of unstriped muscular fibre, and an internal mucous membrane. The fibrous coat is continued into the tunica albuginea of the kidney, and is composed of ordinary connective and elastic tissue. The muscular coat of the ureters consists of three layers. The innermost is composed of longitudinal fibres, the middle of transverse, while the external and weakest is again made up of longitudinal fibres. In the pelvis the arrangement is the same. In the calices the muscular layers become thinner, and are finally wanting at the borders of the papilla?. The mucous membrane is thin, tolerably vascular, and without glands and papilla?. The epithelium is in layers, and is characterized by the size and form of its elements. The cells in the deep

HISTOLOGY OF TEE URINARY ORGANS. 27

layer are round and small ; in the middle layer they are cylindrical and spherical, and possess prolongations; while in the outer layer they are many-angled and flattened, and vary considerably as regards size. (PL I., A, 2.)

The Bladder possesses the same arrangement of layers. The muscular layer is often considerable, but the fibres run so irregularly that a schematic representation is impossible. The internal layer is found to be made up of a network of circular fibres, which form oblique and cross meshes about the neck of the bladder, and are in greatest quantity around its mouth, forming the sphincter vesicae. Upon these circular fibres lie the more external muscular fibres, which run in different directions. The trigonum Lieutaudi consists simply of a thickening of the layers of connective tissue extending from the ureters to the caput gallinaginis. The mucous membrane has (except at the trigonum) a dense submucous layer, which is tolerably rich in blood-vessels and nerves, especially at the fundus and neck. In the neck and toward the fundus of the bladder are found glands formed like bunches of grapes, which have a cylindrical epithelium and mucous contents.

The epithelium of the bladder is of several coats, and varies like that of the ureters in its different layers. The innermost, which lines the cavity of the bladder, is composed of cells which show a more flattened appearance, but differ greatly in size and shape. The middle layer is formed of young cells with conical ends turned away from the cavity of the bladder. These prolonged ends often extend into the deep layer. The deep layer is composed of irregular oval cells, which, as opposed to the middle layer, have their smaller ends in the direction of the cavity of the bladder. (PL I, A, 3.) The blood-vessels of the bladder are the arteria vesicalis, su perior and inferior, springing from the arteria hypogas trica. These enter the bladder wall at the fundus piercing the muscular layer in an oblique direction Here they give off branches, which break up into capil laries in the layer of connective tissue beneath the epi thelium. The nerves are found in greatest abundance at the fundus, in the connective tissue of which it is possible to recognize the axis cylinders of their fibres. Their terminations are unknown. The blood-vessels and nerves of the ureters are similar to those of the bladder.

The Male Urethra has a corpus cavernosum with a fibrous coat and loose tissue similar to that of the penis, only much more delicate. It has a glandular organ, the prostata, which supports it. The mucous membrane permits to be seen beneath it a layer of connective tissue, rich in elastic fibres. External to this are transverse and longitudinal smooth muscular fibres, both in the pars prostatica and membranous portion of the urethra.

The epithelium of the male urethra is composed of cylindrical cells (PL I., B, 1), but in the forward half of the fossa navicularis we find papillae and pavement epithelium. The epithelium of the ducts of the accessory glands, as the prostate, Cowper's, and Littre's, and that

HISTOLOGY OF THE URINARY ORGANS. 29

of the vesicula prostatica, is cylindrical and almost indistinguishable from that of the urethra (PL I., A, 4 and 5, and B, 3).

Tlie Female Urethra has no bulb ; the mucous layer is very vascular, and is lined with pavement epithelium (PL I., B, 2 and 3). Only a small number of Littre's glands are found.

CHAPTEK II.

THE EXCRETION OF THE URINE.

The function of the kidneys consists in the secretion of the urine ; that of the bladder and urinary ducts, in the gradual collection, retention, and discharge of the same. A perfectly satisfactory explanation of the secretion and excretion of the urine in all its details is wanting.

Bowman advances the theory (in which he is supported by the anatomical construction of the kidneys) that the epithelial cells are the secretory organs, and that from the glomeruli only water escapes, which extracts the other constituents of the urine from the epithelial cells.

Ludwig bases his theory upon the varying blood-pressure in the renal vessels, and the interchange of constituents by osmosis through the animal membranes. He assumes that the pressure in the glomeruli is greater than in the capillary system immediately surrounding, and that consequently a profuse exudation of water occurs from the Malpighian tufts, which contains dissolved salts (also blood serum, a little albumen, and fat-

THE EXCRETION OF THE URINE. 31

globules). Accordingly, one finds in the urinary canals thin urine and in the surrounding capillaries thickened blood. These two fluids of such different densities, separated by a thin membrane, cause a ready osmosis, by means of which water from the urinary tubes enters the thickened blood ; on the other hand, the urinary tubes receive from the blood the products of retrograde metamorphosis (urea and salts). In this manner the watery urine becomes more concentrated and richer in urea and salts — a true urine. The absence of albumen may be accounted for from the fact that it passes through animal membrane with much difficulty and only under great pressure. Under a pathologically heightened blood-pressure in the glomeruli (as stagnation of the renal venous system), one always finds albumen in the urine, but never under a physiological blood-pressure. Though this theory explains many physiological and pathological facts, it does not show how an acid urine can be secreted from an alkaline blood-serum. Hence the mechanical theory of Ludwig attributes to the glomerulus a process of filtration, and in the further course of the urinary tubes a process of osmosis, the office of the epithelium being wholly left out of consideration.

According to Goll and Max Hermann, the difference in pressure between the contents of the blood-vessels and the urinary tubules constitutes a chief motive power which forces the urinary constituents of the blood into the urinary tubules. Consequently if the blood-pressure in the renal artery is increased, then there is an increase in the amount of mine secreted; but if the blood-pressure in the renal artery is diminished, or the pressure in the ureter approaches the normal blood-pressure in the artery, then is the secretion of urine lessened or made to cease entirely, long before the pressure in the ureter has reached the amount of pressure in the renal artery.

Ustimowitsch and Griitzner have elaborated these theories to such an extent as to demonstrate, by experiments on the dog, that the secretion of urine is not dependent upon the general blood-pressure, but upon the local pressure in the glomeruli of the kidney. If the medulla oblongata of a dog be divided and the general blood-pressure be artificially increased by a current of electricity, the secretion of urine is prevented entirely, for the reason that the small vessels of the kidney become contracted. If now the nerves of one kidney be divided, there ensues a profuse secretion of urine on that side, while no urine flows through the ureter of the other kidney. This is due to the fact that by section of the vaso-motor nerves of the kidneys the smallest arteries become expanded and relaxed, by which means the blood-pressure in these small vessels is increased and the secretion of urine brought about. Ustimowitsch also shows that by a diminution of the general blood-pressure an increase in the secretion of urine ensues. If one, for example, cuts through the sympathetic nerve, which contains the vaso-motor branches for the kidney, the blood-pressure in the aorta is reduced, but at the same time an expansion of the small