On food and its digestion: being an introduction to dietetics

Front matter

I 9 iffl ill II

I lOfff]

ffilJ full

Preface

The following Treatise is intended to describe the process of Digestion, in its natural connection with the Food on

which it operates, and with the purpose which that Food, ; ius elaborated, fulfils.

In so far as it answers to this intention, it differs from of the works on Diet hitherto published. It gives a e complel unt of tl s tns of Digestion,

&s both their structure and function. It illustrates the relation of Digestion to Nutrition, by referring the details of the demand for food to those of that process of bodily waste by which this demand is dictated. Endeavouring specially to harmonise the study of Food with that of Digestion, it everywhere keeps the Natural History of the various alimentary substances in clue subordination to their practical bearing on life and health. Hence, while chiefly discussing the articles of food commonly used in this country, it views these from a rational rather than an empirical aspect : in order to seek out the phy-

A 3 vi PREFACE.

siological principles of their use, bo far as these are cernihle by the light of our existing knowledge. In b! it treats the whole subject of Digestion as a natural subdivision of the "Institutes of Medicine:" and especially dwells on the Physiology of Food, as constituting a I for the Practice of Physic, in reference both to the vention, and to the cure, of Diseasa

Such a plan is so closely akin to that adopted bj the Course of Physiology at St. Thomas's Hospital, tl I 1 make no excuses for reproducing in thimaterials already included in my Lectures on Digest and published as part of the arth In-

testine," in the Cyclopaedia of Anatomy and Physi

As little am I disposed to apologise Eot I not only the matter, but tin' manner, of the Lectin An author will scarcely handle hi- Bubjed aright, he have some definite idea of the readers whom h addressing. And even where I have most di the Course of Lectures above alluded to, I have at imagined myself speaking to an audience like that which it has for many years been my duty to address on the same subject. If, in uttering the ph which I have formed, the desire to suggest, to illi and even (so for as is fitting) to interest and amufl . led me beyond the conventional boundaries of scientific authorcraft, the reader will perhaps recollect that 1 1 specially addressed myself to students : who. as

PREFACE. Vll

are generally glad to receive any illustrations which may help to clear up the obscurities of a subject ; and appear to reserve all their intolerance for pedantry and cant.

Indeed, save as a Lecturer addressing an audience of students, whose specific requirements dictate and limit his duties, I could scarcely have written the following pages at all. The vast field for successful research offered by structural Disease, and the special responsibilities, as to the cultivation of Pathology, which every Hospital Physician by implication undertakes, would of themselves have sufficed to prohibit my entering on the merely curious or literary aspects of the subject of Food. And increasing professional avocations have so trenched upon the scanty leisure at my disposal before beginning this book, that, however restricted its plan, nothing short of the engagements I had entered into could have induced me to finish it.

The delays incident to the paramount claims of practice have not, I trust, prevented my giving a conscientious revision to the whole subject ; and especially to some Dietetic questions attracting great interest in the present day. Violent as is the controversy which these questions seem generally to provoke, it would perhaps be presumptuous in me to aspire to the honour of a condemnation by those holding extreme opinions on both sides. But, failing to obtain this typical success, I shall still hope to have been useful ; both by suggesting some truths for further consideration, and by pointing out some plausible errors, the exposure of which may tend to advance our knowledge.

viil PREFACE.

In accordance with a plan adopted in my Lecture of my estimates of chemical composition are averages from several of the best analyses, the sources of which are noticed. A similar statement will apply to the other estimates here and there introduced. The calculati necessary for all have been carefully made and repeated- It is hoped that this procedure, — which, though it addfl to the labour and responsibilities of the teacher* afford the learner, results instead of processes ; selections of hap-hazard quotations ; and a general view, ingfo number of casual or conflicting detail-, — will be found as convenient to the reader, as it certainly seems to 1 student in the Lecture-room.

The subjects of VOMITING and of T >u:ta i 3 been considered in an Appendix: as being collal the main purpose of the book.

WILLIAM BBINT «

CHAPTER I. Tin: MEED OF FOOD. — BODILY WASTE

0, physical and vital. — Idea of Nutrition. — Channels of Waste. — Chief Constituents of V Carbonic Acid, Water, Urea

and it- Congeners, Salts, &c — S - t these Constituents respectively. — Numerical Summary.— Halations of Food and Waste to the Blood as well as to the Tissues. — Period of total Waste or Renovation of the Body. — Hybernation and Starvation as illustrating these Statement- ....... Page 1

(HAP. II.

Tin: NATURE OF food. — alimentary CONSTITUENTS.

Definition of P 1. — Distinction from Drink. — Relation to other Ingeata.

— Nature of Food. — Its Organic Source. — Hence Contrast and Relations of the Animal and the Plant. — Cliemi.-al Relations of Food to the Body. —Its Variety essential — ZNIilk as a Model Food. — Constituents of Food. — Protein-compounds. — Fats, or Hydro-carbons. — Sugar and Starch, or Hydrates of Carbon. — Water. — Salts . . .39 chap. in.

DIGESTION. ITS FIRST STAGE.

Definition and Summary of the Process. — Mastication. — Insalivation. — Salivary Glands. — Their Structure. — Secretion. — Physical and Che-

; CONTESTS.

mical Properties of Saliva. — Its Quantity. — Stimuli Flo v.-. —

Its Action; mechanical, general, and special Functions. — Influx, various Sources, — Eelation to the Stomach an<i ":<:.. — 1> _

tition : in the Pharynx — in the (Esophagus — at the Cardia

CHAP. IV.

DIGESTION. THE STOMACH.

The Stomach. — Its Shape, Size, Attachment, Situation. — It- Straetm —

Serous Coat. — Muscular Coat. — M f this C

Gastric Contents. — Pyloric Valv ■. — I —

ticular Glands. — Matrix. — Ai S. —

Lymphatics. — Digest i \ < *

perties. — Chemical Proper!

« — Action of Gastric Juice. — Pi

Gastric Digestion . . . .88

chap. v.

DIGESTION. THE SMALL lNIT>Ti:

The Intestine. — Small Intestine. — Duodenum: its thn i —

Mesentery. — Convolutions. — Jejunum. — Ileum. — Muscular C it — Its Movements; as deduced, observed. — Tin j. —

Mucous Membrane. — Vo.lvuhe Connivente*. — Tul 60, — 1 1 • ii 3 or "Intestinal Juice." — Villi. — Their Constituents, including teals. — Their Changes during Digestion. — Absorption oi Fat — I cles; Agminate, Solitary. — Racemose Glands. — A - —

Pancreas. — Its Structure. — Secretion or Pancreatic Jui — sical, Chemical, Properties. — Its Share in Digestion; or A ' Starch, (2) Fat, (3) Protein-compounds. — Liver. — It- Supplj — Its Physical Characters. — Its Structure ; Capsule, V — Is, i '..- Ducts. — Its two-fold Function. — The Bile. — Its Quant iv. flue-need by the Gall-bladder. — Its Composition. — Its two-mid I Bd Excretion, Resorption, — Its Influence on Digestion. — 1*- S m ea — Influence of the Liver on Digestion. — Contrast of Portal and Bloods. — Progress of Digestion in the Small Intestine

CONTEXTS. XI

CHAP. VI.

DIGESTION. THE LARGE INTESTINE.

Large Intestine ; its Measurements, Divisions. — Caecum ; its Shape, Stru c tur e, Openings. — Ileo-caecal Valve. — Vermiform Appendix. — Colon; its Form, Structure. — Its movements; observed, deduced. — Rectum; its Situation, Shape, Structure. — Its Sphincters. — Its Contractions; propulsive, expulsive or Defecation. — Its Folds. — Mucous Membrane. — Arteries of the Intestinal Canal; Superior, Inferior Mesenteric, and their Branches. — Intestinal Veins. — Rationale of the Intestinal Vessels* — Nerves of the Intestinal Canal. — Lymphatics. — Contents of the Large Intestine: Fsdcal, I -Digestion in this

lent. — Office of the Cfecom. — Duration of Intestinal Digestion. — es. — Their Properties ; Sources. — Mechanical Ingredients. — Chemical Composition. — Intestinal and gastri —Their Composition, Nature, and Sources. — Their Relation to Secretion. — Their Absorption. — Relation of Digestion to Nutrition. — Intermediate Circulation. — Digestion, its Expenditure of Force .... Page 199

(HAP. VII. yai:iktii:s OF food. — animal food.

; lients of Food. — Animal and Vegetable. — Their Mixture natural for

Man. — Their Variation contingent — Nutritional Influence of Foods. — Contrast of Animal and Vegetable Food. — Varieties of Animal Food. — Meal or Flesh. Its Chemical Components. — 1. Fibrin. — 2. Albumen. —

■ ••latin. — Itl 5 I, — Nutritional Value of it, and of the Collagenic

Tissues, — -1. I Its Nutritive Value, in

Animal. Vegetable Food. — [ta Dig< stibility, as affected by its Kind, by Climate. — It^ Destiny, when assimilated in Excess. — o. Inorganic Constituents, contrasted with those of Blood. — 6. Secondary Organic Compounds. — Other Kinds *»f Animal Food. — Organic Muscle. — Heart. — Tongue. — Respiratory, Tendinous, Muscles. — Influence of Diseases, Age, Habits of Animal. — Flesh of Birds. — Fish. — Blood. — Brains. — Glands. — Bone. — EggS. — Milk. — Variations in different Animals as to Quality, Quantity. — Influence of Date of Lactation. — Physical Arrangement of Milk. — Cream. — Butter. — Its Components. — Its Nutritive Value. — Cheese. — Its Composition. — Its Varieties. — Its Nutritive Value . . . . . . . .246

Xll CONTENTS,

CHAP. VIII.

VARIETIES OF FOOD. VEGETABLE FOOD.

Vegetable Food. — Its Characters. — Its importance to "National Life.— Value in warm Climates. — Its Variation* by Culta

Climate, Age. — Cereal and allied Grains ; their VaJ their Growth, their Composition. — Pr>\ h A their Proteinous Constituent, Husk, Fat. Stare] tions in other Characters. — Pro- Chemical Changes. — Choice of Breads. — Leguminous Seeds. I mposition. — Nutritive Value. — Potatoes. — Thei I ' Nu-

tritive Value. — Roots and Fruit-. — Their Composition an Shoots, Leaves, &c. — Their Con ad Nutritive Prop*-: I

chap. i\.

I ONDIM

Condiments, their Character. — Tl. ine. —

Salt as illustrating these Relations. [ta to Scurvy. — Effed

Use ; in Man, in Animals. — Acrid or Stunnls I I ts. Their

with reference to Appetite. Circulation, Secretion.—. S] - — as Medicaments. — Complementary Natun Alliaceous Condiments. — Their Varietu - Condiments. — Oils. — Alkaloids. — C or Complementary Foods . . . . .331

CHAP. X.

TEA AND OOFFEEi

Tea and Coffee. — Their Introduction into Europe. — F- suits :' •'

Use. — Their Contrast and Analogy ■ in Eff tfi

Its Source. — Its Varieties (Black and Given V - —

Composition of Tea. and of its Infusion. — Composition of fee, —

Effect of Boasting. — Proximate Ingredients of its Decoction. — Nut: Value of Tea and Cofifee, — Physiological Effects. — Their Relation. — Theory of the economizing Action of Tea and Coffee. — contexts. xiii

searches of Boecker and others hereon. — Resemblances, and Contrasts, of their Action. — Objections to such Views in general ; to these Experiments in particular. — Cocoa and its Preparations. — Their Contrast with Tea and Coffee. — Their dietetic Value . . . Page 344

CIIAP. XL

ALCOHOLIC DRINKS.

Alcoholic Drinks. — Their Relation to Food. — Their Classes. — Wine. — Its Typical Varieties. — Their Composition: as influenced by various Circumstances. — Bordeaux and Burgundy. — Sherry, Madeira, Port. — Efferdng Wines. — spirits. — Been or Ales. — Physiological Effects of Alcoholic Drinks. — Pathological Effects. — Action of Alcohol on the Functions. — On the Metamorphosis of the Body. — Researches of Boecker and others. — Objections to their Conclusions ; to their Facts. — Elimination of Alcohol. — Its Influence on Vicarious Secretion. — Its Action on the Organism. — Its Influence on Bodily Temperature, — On Bodily, Mental Exertion. — Its Indirect Value. — Its Reaction, — Its Influence on Longevity, in Individual-, Populations. — Teetotalism. — Influence of Alcohol on Digestion ; on Ingestion. — Risks of Sudden Abstinence 365

CIIAP. XII.

00OKEBT.

Importance ay. — Comparison of Paw and Cooked Flesh. — Di-

•ve Import of the Changes wrought by Cookery. — Summary of its Advantages. — Process of roasting Meat — Process of boiling Meat. — Var; Boiling; their Objects, and Processes. — French Pot-au-feu

as one of these Varieties. — Baking. — Stewing. — Soups. — Their Objects, and corresponding Varieties, — Spanish Puckero. — Cookery of Flesh as affected by its Decomposition. — Economy of Cookery . 399

CIIAP. XIII.

CHOICE OF FOOD, OR DIET.

Diets ; as Mixtures of the preceding Articles of Food. — Difficulties of their Calculation. — Value of Physiological Chemistry in the Choice of Food. — Absolute Quantity of Food. — Results of Deficiency of Food. —

XIV CONTEXTS.

Test of a good Diet. — Uses of its Variety. — Office of Physiology in

reference to Dietetics. — Chief Circumstances affed —Diet as

modified by Age ; in Childhood, in Old Age. — Diet as modifii

— By Habits of Life ; Confinement, Inaction. Mental Exertion. — By

Climate; in Arctic, Tropical, Regions. — By B ice. — By !•- —

Diet in Diseases of the Digestive Organs. — In Diseases ol El

of Repletion. — Repletion; general and easoaL — Repletion from eh>

Elimination ; from general Congestion. — Relation of Instinct *

Diet in special Diseases, how appraised, — Fever; —

Value of Alcohol in Disease. — Clue to it- Ofl 8, I A

ferable Mode of its Administration. — Principle of the Choice of Food

and Stimulants in acute Disease

Appendix A. — Vomiting .....

Appendix B. — Dietaries .....

LIST OF VOOD-EXGRAVINGS.

Fig. Page

1. Conglobate Gland of the Month ; after Koelliker . . 73

2. Diagram of two Ducts of a Lobule ; after Koelliker . . 74

3. Two V.-i- roglobate Gland j after Koelliker . . 75

4. Capillaries of a Lobule ; after Hyde Salter . . .79

5. Stomach inflated and dissected* to show its deeper Muscular

6. Fibre-cells of the Stomach . . . . .95

7. Section of the Pyloric Valve . . . . .97

8. Diagram to illustrate Peristalsis in a closed Tube . . 100

9. Diagram to show the Movement of the Food in the Stomach . 101

10. Vertical Section of the Stomach* showing its Structure . . 106

11. Upper part of a Stomach-tube, showing its dimorphous Cell-

12. Arteries of the Stomach . . . . . .111

13. Vessels of the Gastric Mucous Membrane, as seen in a vertical

14. Superficial Capillaries of the Gastric Mucous Membrane . 114

15. Stomach and Intestinal Canal ..... 133

16. Bundle of Fibre-cells from the Muscular Coat of the Intestine . 137

17. Small Intestine prepared to show the Valvules Connivmtes . 144

18. Intestinal Tubes from the Jejunum .... 146

19. Superficial Capillaries of the Intestinal Mucous Membrane . 151

20. Vertical Section of the Jejunum, showing its Structure . . 152

21. Villus of the Jejunum during fasting . . . .153

22. Vessels of two Villi, injected ..... 155

23. Villi of the Calf, showing their Lacteals ; after Koelliker . 157

24. Villus prepared to show its Muscular Structure ; after Koelliker 158

25. Villi of the Dog, wrinkled by contraction . . . 161

XVI

LIST OF ^VOOD ENGRAVINGS*

Fig.

26. Similar Villi, showing the separation of their Epithelium and

Body . . .

27. Villus of the Dog, during Digestion

28. Agminate Follicles ; after Koelliker

29. Agminate Follicles distended ; after Boehm

30. Portion of a duster of such Follicles

31. Section of Intestine showing an Agminate Follicle

32. Vessels of three Agminate Follicles of the Rabbit ;

33. Vertical Section of Duodenum, Bhowing aD

34. Diagram of two Duet- of a Lobule; the 2, .

35. Relations of the Duodenum and Fane

36. Under Surface of the Liver ....

37. Transverse Section of a Portal Canal : after Kieroan

38. Longitudinal Section of Sublobular Vein ; man

39. Longitudinal Section of a small Portal Canal: after Kiernau

40. Portal Venous Plexus; after Kiernau

41. Network of Hepatic Cells and I

Koelliker ......

42. Commencement of the Interlobular I

43. Large Entestine

44. Csecum, prepared to show the arrai

45. Viscera of the Male Pelvis, showing th< turn

46. Distribution of the Superior M Lrtery .

47. Distribution of the Inferior Mesenteric Artery

48. Branches of the Portal Vein ....

Page

162 164

107 168 ox TOOD A^D ITS DIGESTION.

CHAPTEB I.

Till; NEED <)F FOOD. — BOJDIL1 WASTE.

. physical and vital. — Idea of Nutrition. — Channels of Waste. —

Chief Constituents of Waste, or Egesta: Carbonic Acid, Water, Urea and

aers, Salts, flee. - Sources of these Constituents respectively. —

Numerical Summary. — Relation of Food and Waste to the Blood as well BS t<» the Tissues. Period of total Waste or Renovation of the Body. — Hybernation and Starvation as Qlustrating these Statements.

Is the animal economy, income is regulated by expenditure; and the ingestion of food replaces that loss of substance which the body is continually undergoing.

Even the hardest materials of the earth's surface are continually experiencing radual disintegration, as a

result of the various physical processes to which they are exposed. Such processes may be instanced in the attrition and solution of solids, the evaporation of liquids, and the diffusion of gases. And hence, when we turn from these inorganic substances to the animal fabric, and consider its slight cohesion, the friction which its locomotion implies, its large watery constituent, and the feeble chemical affinities which enchain its elementary

B

'J atoms, we shall scarcely be surprised to find that the rapidity of its waste far exceeds that of the inanimate solids around us.

But the rate of waste, and the consequent need replacement, both depend far less on simple physical causes of this kind, than on certain - which

specific to the organised body. These actions, which, in the aggregate, make up what we term Lin:, do much imply, as actually consist in, a perpetual pr< flux and metamorphosis, which engages all of the body, and conducts their several through various successive phases of composition, t<» an effete and useless state, in which they arc finally i from the organism.

Hence, whatever the share taken by the physi actions of diffusion, solution, friction, and evaporation, in the removal of the substance of the body, they in any sense the true causes of it- process of \ the real sources of its egeata or losses. They are but, it were, the janitors ot the animal fortress; the nal and amount of the matter- passing oat by those portali which they stand being always dictated by the big forces of the life that rules within.

The growth of the young animal proves that its on the whole, outweigh its losses. And it is s reversal of this disparity which causes the aged animal to dwindle and decay towards the close ^ its allotted term of life. But in either case, the process o{ nutrition itself is far m affected than is the mere quantity of its materials, or of its products. Hence, in summing up the chief detaik that waste which forms one extremity of nutritional life, with a view to contrasting the indirect information thus gained with that more directly derivable from a study of food itself, we may conveniently restrict ourselves to that ideal or abstract view of nutrition which regards it as effecting the mere maintenance of the adult bod}'. And, while such a summary cannot well suggest any lively or definite ideas of this process without often referring to the quantities presumably concerned, these estimates must be received with an explicit acknowledgment that their inherent inexactness is increased by their ignoring many influential circumstances — age, sex, idiosyncrasy — without which they are quite inapplicable to the case of any individual.*

The losses, or rrjesta, of the organism leave it by four channels. The excrement and the urine respectively convey away a moist solid mass, and a much greater bulk of a liquid containing a large proportion of dissolved solids. The skin, besides that gradual loss of substance from its surface which, under many circumstances, becomes perceptible to the naked eye, insensibly discharges vapours which arc easily augmented and aggregated into the liquid state of sweat. The lungs likewise discharge vapours and gases; of which the former are often seen to collect as drops of liquid upon neighbouring objects, while the latter may be recognised as carbonic acid and ammonia by the application of appropriate tests to the

* Perhaps we may find the nearest approach to accuracy in supposing these estimates to refer to a healthy male, 35 years old, 5| feet high, and 10 stones in weight.

B 2

4 THE XEED OF FOOD.

air exhaled. Hence, any division of these solid, liquid, and gaseous, only regards their balkier constituent. As in the division of alimentary su into food and drink, all exact boundary fails as. feces are not only charged with liquids, hut mechani entangle, as well as dissolve, gases in their substance. urine, again, contains gases in a state of solution. Tinlungs, beside exhaling volatile liquids, which are capabl condensing at a very moderate diminution of the pulmonary (105° F.) temperature, giv< I nailer quantities of liquids, and even of solids, which are dowb by ciliary movements ii]> the bronchial tubes that I the channels of exit for their expired tad vapours.

Lastly, while various casualties may determine tin- \ \ or liquid form for the water which is given off bj skin, it may be questioned whether it- ammoii . acid, and even its fatty acids, _ 1 in

these volatile or gaseous forms, <>v are thrown out the lowermost strata of the cutaneoofl tissues in a liquid (perhaps even in a solid) state.

As the chief constituents of these losses, we maj enun rate carbonic acid, water, urea and it- congenero, i: _ salts, and sundry organic (and even d substances.

The carbonic acid riven off from the body daily may be estimated at about '2 lbs.; a weight which, at ordin pressure and temperature, would correspond t-> a bulk about 17 cubic feet. Of this quantity, it IS Me that

a single ounce, or halt a cubic foot, is all that finds it- \\a\ out by the skin: the remainder being exhaled from the lungs in the air expired, the carbonic acid of whiei about a hundred-fold more abundant than that of the inspiratory air (-04 and 4 per cent, respectively).

The quantity of water daily set free seems to be about 6 lbs.* Of this rather less than half appears to be given off in the feces and urine (the latter containing about ten times as much as the former), and rather more than half by the skin and lungs. Of the latter moiety, again, the whole of which is often included under the term transpiration, the pulmonary share may be regarded as not more than 1 lb.; the skin furnishing the remaining 2 — 2\ lbs., usually in the form of watery vapour.

These proportions fluctuate atly, as to require even

than the usual qualifications of such estimates. The watery vapour exhaled may be regarded afl tending to saturate the inspired air, and therefore as vastly reduced by any previous approach to saturation in the surrounding atmosphere External warmth and active bodily exertion, which greatly t increase the water of the cutaneous secretion, correspondingly diminish that of the urine, and even

of tie

Urea and its congeners are justly regarded with extreme

interest in respect to the quantitative aspect of nutrition. So small an amount of nitrogen is given off by the skin and lungs, whether pun- or in combination ( ammonia, and even by the intestinal evacuations (barely 3 per cent, of the daily loss of azote), that it is by this constituent

* The weigh tfl mentioned are those most familiar to a medical reader : v. pounds avoirdupois; ounces, drachms, and grains of apothec; weight.

t Valentin found the amount thus given off in a certain time to be quadrupled by active movemi

B 3 of the urine, which contains nearly 50 per cent, of nitrogen,

we may best measure both the waste of the azor

and the quantity of azotised food necessary to replace it.

About 480 grains, or 1 oz., would seem to be a tolerably exact estimate of the urea excreted daily by a healthy male adult. Eeducible to scarcely more than half this quantity for the female, and a quarter for the child or the aged person, and doubled, or halved, by diseases in which b waste exceeds (fever) and falls below (chronic heart disease) the standard respectively, it is equally amenable to two other sources of variation. Of these, one, fht natu-

rally Be expected, is apparent rather than real, bei a diminution in the urea excreted from the body by a diseased kidney as is partly counterpoised by its alio* the quantity retained to accumulate in the poisoned Mood. In the other the diminution or incn quantity ifl <ii< -

tated by the azotised constituent of the food; being by a flesh diet, lowered by a vegetable one, and, lastly, reduced to a minimum (or dietetic » r») by the withholdance of all azotised food.

Uric acid and ammonia, occurring in wry small prop tion* in healthy urine, may be estimated as together amounting to 4 per cent, of the above quantit area

and of nitrogen.

The salts set free from the body are far too imperfectly known, both as regards their quantity and quality, justify any exact quantitative estimate. In respect to the skin, the sweat, which is said to contain about one per c of fixed ingredients, includes among these much chloride * According to Vogel. about 7 and 10 grains per day respe sodium, and further liberates much ammonia in combination with hydrochloric and organic acids. Its sebaceous secretion seems to be chiefly margarate and oleate of soda and ammonia. Its horny epithelial desquamation, which contains about one per cent, of inorganic matter, yields phosphate (and carbonate?) of lime and magnesia.* And even supposing the vaporous or insensible perspiration to contain less of saline constituents than the composition of the liquid sweat would seem to imply, the total inorganic salts of this daily loss must amount to something considerable (50 — 100 grains); while its salts of ammonia presumably sot froe. in the liquid or solid form, a much larger proportion of this alkali than would be conjectured from that quantity of it which can bo detected by the ordinary tests fur this volatile alkali in the free state. The excrement probably dismisses from the body not more than. 40 or 50 grains of salts daily : in addition to that larger and more insoluble saline constituent which it contains in the shape of alimentary residue. Phosphates of the earthsand alkalies, sulphates, and but little chlorides, are its chief components.

It is in the urine that we find the nearest approach to accuracy of estimate, as woll as the largest items of waste, in respect to these ingredients of the bodily mass. The chief fixed salts of the urine may be regarded as setting free from the body daily about 4^ drachms of chloride of sodium, 4 of sulphates (chiefly of soda and potash), 2 of acid phosphate of soda, and 1 of phosphates of lime and magnesia.

* Anselmino in Tiedemann's Zeitsehrift, b. ii. s. 321 — 342. B 4

In addition to the preceding ingredients, however, the body evidently discharges, by every channel of excretion, other substances, only less worthy of notice in the circumstance of their smaller quantity. The albumen, epithelium. and fatty matters of the skin ; the bile, mucus, and epithe-* Hum discharged from the bowels ; the colouring and other extractive matters of the urine: and, lastly, the quasi albuminous film thrown down from the breath of anin when respiring in a confined space; — all these together considerably increase the total of waste, little as each may severally add to its amount.

We may now attempt to trace back these several oonstituents of the daily waste into the body itself. The carbonic acid, given off, as we have noticed, from the -kin as well as the lungs, is further shown, by both physical and chemical examination, to be introduced into the blood in the capillaries throughout the whole body, where it marks the transition from arterial to venous blood by the stril change it impresses on this fluid. It is true that, in the rush of blood occasionally Bent to an active gland at the period of its intermittent action, this change of colour appears to be subordinated and disguised by the vast quantity of fluid then undergoing a rapid transit, during which it yields up certain of its constituents. This very fact, however, not only permits, but suggests the statem abundantly confirmed by all the other phenomena of tinprocess — that it is a change, an oxidation, a combustion of all the bodily tissues which forms the source of the animal heat, and pours into the blood that stream carbonic acid, afterwards chiefly (but not exclusive removed by physical diffusion in the lungs from the organism it would speedily poison by its further accumulation.