CORNELL UNIVERSITY LIBRARY CO I CDs N) = ol o= Oil ens o>= ol co= 0>i ^ Ol o Ul u _a » TJ ID WO !o COO 3 -to ; -» 00* • o -^~ la cn§ ■01 :3 < ia 2. §0- •< Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003556036 TREATISE ON FOOD DIETETICS, PHYSIOLOGICALLY AND THERAPEUTICALLY CONSIDERED. F. "W. PAVY, M.D., F.R.S., FELLOW OF THE EOYAL COLLEGE OF PHYSICIANS; PHTMCIAN TO, AND LECTXJttEB ON PHYSIOLOGY AT, GUY'S HOSPITAL. SECOND EDITION. LONDON: J. & A. CHTJRCHfLL, NEW BURLINGTON STREET. SIMPK1N, MARSHALL, & CO., STATIONERS' HALL COURT. 1875. (All rights reserved.) %' INSCRIBED TO THE EIGHT HONOURABLE LYON PLAYFAIR, M.P., O.B., F.R.S., AS A MAKK OP APPEECIATION OF HIS SCIENTIFIC LABOURS IN RELATION TO FOOD, AND IN ADJURATION OF THE SERVICES HE IS NOW RENDERING IN HIS POLITICAL CAREER. PKEFACE TO THE SECOND EDITION. A large impression having become exhausted in less than a year, I feel myself warranted in concluding that I was not mistaken in judging that a work of the kind produced was wanted, and at the same time am emboldened to cherish the idea that the labour bestowed has not proved fruitless in usefulness to others. The favorable reception accorded to the first edition has served alike as a source of gratification to me and a stimulus to renewed exertions to render the work worthy of appro- bation. Without presuming to think that there does not still exist much room for improvement, I hope that some- thing in that direction has been effected by the revision which has been carried out. Wherever it has appeared to be required, the wording has been altered to render the meaning clearer ; various modifications (in part suggested by the valued hints of reviewers) have been introduced; and a considerable amount of new matter added : notably, attention may be directed to the preliminary part of the section on Wine as having undergone extensive amplifica- tion. I am glad to avail myself of the opportunity here afforded of expressing my thanks to those who, since the appearance of this work, have supplied me with information drawn from scattered sources upon the subject of Pood. 35, Gkosvjbnok Street, Grosvetjor Square ; June 1st, 1875. PREFACE TO THE FIRST EDITION. In the Preface to the second edition of my work on ' Digestion, its Disorders, and their Treatment/ I mentioned that I had originally intended to add a section on Food to the contents of that volume, but that for the reasons given I afterwards determined to publish a separate treatise on the subject. Thus originated the present work, which, with the progress of time and a large consumption of midnight oil, has grown to dimensions far exceeding those I had at first contemplated. From the fact that the subject of Food is one of deep concern, both to the healthy and the sick — that the informa- ] tion which has been obtained during the last few years has completely revolutionised some of the cardinal scientific notions formerly entertained — and that no modern systematic j treatise of the kind here presented exists in the English language, I have been encouraged to think that the task I. have undertaken may not be deemed superfluous. Whatever j the results attained, I have steadily striven, sparing no pains for the purpose, to render the work produced instructive and : useful. On account of the change recently introduced in chemical notation, I have given both old and new formulae, placing the latter within square brackets after the former. 35, Gbosvenor Street, Grosvenor Square; March, 1874. CONTENTS. Introductory Remarks on the Dynamic Relatioks of Food ...... 1—8 Matter and Force, 1. Correlation of the Physical Forces, 1-2. Equivalent of heat in mechanical motion, 2. Force and energy — dis- tinction explained, 2-3. Analogy between living matter and a machine, 4. Forms of force derived from the sun, 5-6. Analogy between the animal system aud a steam-engine, 6-7. Life implies change, 7. Dormant vitality, 8. On the Origination of Food .... 9—20 Power possessed by animals of forming one kind of organic com- pound out of another, 9-10. Influence of the solar force, 10-13. Action of vegetable life, 13-16. Formation of organic compounds, 17-19. Eesults of animal and vegetable life, 18-20. The Constituent Elements of Food . . .21 Alimentary Principles : their Classification, Che- mical Relations, Digestion, Assimilation, and Physiological Uses .... 22—140 Distinction between alimentary principles and alimentary sub- stances, 22. Separation of food and drink not physiologically correct, 22-23. Classification of food, 23-26. The Nitbogenous Alimentary Principles, 27—86: — Albuminous or proteine compounds — animal and vegetable proteine compounds, 27-30. Gelatinous principles, 30-31. Digestion of the nitrogenous principles, 31-34. Action of pancreatic juice, 35-37. Production of albuminose, 38-40. Uses of nitrogenous matter, 40. Its relation to force-production, 41-42. Experiments on the elimina- tion of nitrogen, 42-61. Resume on nitrogenous food and muscular action, 61-62. Heat-production, 63-64. Varied amounts of urea excreted on vegetable and animal diets, 64. Metamorphosis of nitro- genous focd, 65-75. Force value of nitrogenous food, 76-79. Nitro- genous matter as a source of fat, 80-83. Alimtntary value of gelatinous principles, 83-86. Vlll CONTENTS. PAGE The Non -Nitbogenous Alimentaey Principles, 87 — 104 : — Hydro-carbons, or fats, 87-90. Uses of fat, 90-92. Fat as a heat- producing agent, 93-94. Oxidizable capacity of fat, 94-95. Fat in relation to muscular force-production, 96-101. Actual force-value of fat, 101-104. The Cabbo-Hydbates, 105-128 : — Starch, 105-108. Sugars, 108-112. Gum, 112-113. Dextrine, 113. Cellulose, 113-114. Lignine, 114. Lactic acid, 114. Assimilation and utilisation of the carbo-hydrates, 114-118. Their destination, 119. Power of aiiimals to form fat, 119-120. Production of foie gras, 121-122. Conversion of the carbo-hydrates into fat, 123-126. Ultimate use of the carbo-hydrates, 127-128. Ternary principles not carbo-hydrates : — Pectine, vegetable acids, alcohol, 129-135. The Inobganic Alimentaey Pbinciples, 136-140 :— Water, 136. Saline matter, 136-140. Alimentahy Substances .... 141 — 424 Animai. Alimentaey Substances, 141 — 226 : — Their classification, 141-142. Varieties of meat, 142-153. Un- wholesome meat, 153-162. Poultry, game, and wild fowl, 162-165. Fish, 165-173. Shell-fish, 173-178. Eggs, 178-181. Milk, 181-197. Butter, 197-200. Cheese, 200-204. Animal foods sometimes but not ordinarily eaten, 205 — 226 : — Cannibalism, 205-206. Mammals, 206-214. (Horseflesh, 211-213.) Birds, 215-216. Reptiles, 216-218. Fish, 218-219. Insects, 219-220. Earth-eating, 221-223. Table of references, 223-226. Vegetable Alimentary Substances, 227-337: — Farinaceous seeds, 227-260. The cerealia, 228-260. Wheat and flour, 229-234. Bread, 234-240. Miscellaneous articles prepared from flour, 241-243. Unwholesome wheaten products, 244-246. Oats, 246-249. Barley, 249-251. Rye, 251-252. Indian corn, 253-255. Rice, 255-257. Millet, 257-258. Buck-wheat, 258-259. Quinoa, 259-260. Leguminous seeds, or pulses, 260-264. Oleao-inous seeds, 265-269. Tubers and roots, 270-282. Potatoes, 270-275. Herbaceous articles, 282-291. Products of the cabbage tribe, 283- 285. Various vegetables, 285-291. Fruity products consumed as vegetables, 291-293. Esculent fungi, 293-298. Varieties of fruit, 298-323. Bark, 324. Saw-dust and woody fibre, 324. Vegetable butter, 325-326. Saccharine preparations, 325-326. Saccharine products, 326-332. Farinaceous preparations, 332-337. Bevebages, 338—423 : — Water, 338-346. Non-alcoholic, exhilarating, and restorative beverages, 346-370. Tea, 348-354. Representatives of tea, 355-356. Coffee, 356-362. Fictitious coffee, 362. Chicory, 362-363. Gua- CONTENTS. IX PAGE rana, 863-365. Cocoa, 365. Fictitious cocoas, 370. Coca, 370. Alcoholic beverages, 370-423. Effect of alcohol on the system, 371- 377. Beer, 377-381. Cider, perry, 881-382. Wine, 382-417. French wines, 407-410. German wines, 410. Hungarian wines, 410-411. Greek wines, 411. Italian wines, 412. Australian wines, 412. Port and other wines of Portugal, 412-414. Sherry and other Spanish wines, 414-415. Marsala, 415-416. Madeira, 416. Cape or South African wines, 416-417. Miscellaneous fruit and other wines, 417. Mead or metheglin, 417. Spirits, 417-422. Liqueurs, 422-423. Condiments, 424. Tbe Pbesebyation of Food . . . 425 — 431 Modern processes of preservation, 425. Four means of preserving food, viz. hy cold, drying, exclusion of air, and use of antiseptics, 426-431. Peinciples op Dietetics .... 432 — 473 Composition of milk and the egg, 432. Researches of the Paris Gelatine Commission, 433-436. Position held by nitrogenous matter, 437-439. Question as to the necessity of fats and carbo- hydrates, 439-440. Adaptation of food to demand, 441-442. Liebig's estimate of the nutritive value of food, 443. Frankland's estimate of the force-producing value of food, 444-448. The appetite as a measure of capacity for work, 448-449. Nitrogenous matter required for physical development, 450. Human labour more expensive than steam work, 451. Moleschott's table of a standard or model- diet, 452. Adjustment of food to climate and work, 453-456. Table showing per-centage composition of various articles of food, 457-458. Playfair's dietaries, 458-461. Workhouse dietaries, 461. Prison dietaries, 461-463. Tables of hard and light labour diets, 464. Industrial employment, penal, and punishment diets, 465-466. Instances of limited diet, 467-468. Table from Payen of per-centage value of food in nitrogen and carbon, 469-470. Out-going of nitrogen and carbon as a diet basis, 471-473. Pbactical Dietetics .... 474 — 537 Kind of food best adapted for the support of man, 474. Varieties of diet consumed hy different nations : — Arctic regions, 475-477 ; North American Indians, 478; Mexico, 478-479; Pampas Indians, 479-480 ; Guachos, 480 ; Natives of Australia, New Zealand, 480- 482; of the Friendly Islands, 482; Otaheite, 482 ; Feejee Islands, 482; Tanna, New Caledonia, Savu, 482-483; Sandwich Islands, 483-484; China, 484-485; Japan, 485; India, Ceylon, 485-486; Africa, 486-491 ; Mixed food the natural diet of man, 491. Vege- tarianism, 491-492. Dietetic value of meat often over-estimated, 493. A certain amount of fresh food necessary to health, 494. b X CONTENTS. PAGE Effects of animal and vegetable food compared, 495-500. Proper amount of food, 500-505. Effects of excess and deficiency of food, 505-509. Times of eating, 509-518. Culinary preparation of food, 518-525. Diet of Infants, 526-531 : — Woman's milk, 526-528* Milk of lower animals, 528-530. Fari- naceous food, 530. Liebig's food, 531. Diet foe Training, 532-537. Object of training, 532. Old and new systems, 533-536. Oxford and Cambridge systems, 536-537. Thebapetttic Dietetics .... 538 — 596 General considerations, 538-541. Diet for gout, 541-543. Influences of food, 543-544. Principles of dieting for thinness and stoutness, 544-546. Reduction of corpulency, 546-549. Dietary for the diabetic, 549-551. Ill effects of restriction to salted and dried pro- visions, 551. Regulation of amount of fluid, 552-553. Effect of varieties of food on the urine, 553-556. Pood for weak digestion, 556-559. Food for dyspepsia,'560-561. Pood for disordered states of the intestinal canal, 562-563. Dietetic Peepabations foe the Invalid, 564-573. Hospital Dietabies, 574-596 : — Guy's Hospital, 574. St. Bartholomew's Hospital, 575-576. St. Thomas's Hospital, 576. London Hospital, 577. St. George's Hospital, 578. Middlesex Hospital, 579-580. University College Hospital, 580-581. King's College Hospital, 581. St. Mary's Hospital, 582. Westminster Hospital, 583. Seamen's Hospital, 584. Leeds General Infirmary, 584-585. Manchester Royal Infir- mary and Dispensary, 585-586. Birmingham General Hospital, 586-587. Newcastle-upon-Tyne Infirmary, 587-588. Edinburgh Royal Infirmary, 588-589. Glasgow Royal Infirmary, 589-590. Richmond, Whitworth, and Hardwicke Hospitals (Dublin), 590-591. Bethlem Lunatic Hospital, 591-592. St. Luke's Hospital for Lunatics, 592-593. Hanwell Lunatic Asylum, 593-595. Colney Hatch Lunatic- Asylum, 595-596. Index ...... 597-613 CORRIGENDA. Page 322, 4th line from bottom, for mangipera read mangifera. „ 384, line 22, after " higher duty," insert " of 2s. 6d. per gallon." INTRODUCTORY REMARKS ON THE DYNAMIC RELATIONS OP POOD. The discoveries and inductions of the present age have thrown a new light on the physiology of food. Around us we have to deal with Matter and Force — the one a substantive entity, the other appreciable only as a principle of action. It has long been known that matter (as cognisable in our own era) can be neither created nor destroyed. It may be variously combined and modified, but it remains the same in essence and unaltered in amount. Force, also, has recently been recognised as similarly con- ditioned ; and in order that the bearings of food in relation to this principle may be understood, some preliminary conside- rations explanatory of the views now entertained regarding it are necessary. To start, then, we may take it as accepted that, under present conditions, force, like matter, can neither be created nor destroyed. " Ex nihilo -ni>iil fit " and " Nihil fit ad nihi- lum " form axioms that must be admitted to be incontro- vertible. If we except the inconsiderable accession derived from the occasional descent of a meteoric body, the earth's matter remains fixed in amount. It is otherwise, however, with respect to force. Under the form of heat and light, force is constantly being transmitted to us from the sun ; and it is from the force thus derived that, in a manner to be explained further on, life on earth originates and is sus- tained. In enunciating his doctrine on the " Correlation of the Physical Forces," Grove demonstrated that one kind of force 2 INTEODUCTOEY EIMAEKS. was capable of producing another. His views were first made known at a lecture delivered at the London Institution in 1842. The word " correlation" he employed as mean- ing "reciprocal production — in other words, that any force capable of producing another may in its turn be produced by it." The position sought to be established was that heat, light, electricity, magnetism, chemical affinity, and motionj are all correlative, or have a reciprocal dependence — that either might produce the others, and that neither could origi- nate otherwise than by production from some antecedent force or forces. *% Just at this time the same field of inquiry was being| investigated by other workers. While Grove was asserting! that the great problem awaiting solution in regard to the correlation of physical forces was the establishment of their equivalent of power, or their measurable relations to a given standard, Mayer, Joule, and Helmholtz were announcing the actual equivalents themselves. Mayer, of Germany, had the priority in the publication of his researches. As a member of the medical profession he approached the subject through its relation to physiology. In 1842 he propounded, in its full comprehensiveness, the doctrine of the " Conservation of Force." Nearly at the same time Mr. Joule, of Manchester, dis- covered the equivalent of heat in mechanical motion. He had been led to prosecute researches in that direction, with the view of ascertaining the relative value of heat and motion for the advantage of engineering science. He foundjl that what sufficed to raise the temperature of a pound of water one degree Fahrenheit would, under another mode of action, raise 772 pounds a foot high ; or, putting it con- versely, the fall of 772 pounds of water from a height of one foot would give rise to an amount of heat sufficient to elevate! the temperature of one pound to the extent of one degree Fahrenheit. Thus the mechanical work corresponding to the elevation of 772 pounds a foot high, or, what comes to the same thing, one pound 772 feet high, forms the dynamic equivalent of one degree of heat of Fahrenheit's scale. It is necessary to state here that the term " force," when used in a strict sense, is employed under a more limited ON THE DYNAMIC RELATIONS OF FOOD. 3 acceptation now than formerly. Originally it represented what is now distinguished as both "force" and " energy." By "force," under a rigid signification, is understood the power of producing energy ; by " energy " the power of per- forming work. To give an illustration : power has force, the cannon-ball energy ; but to speak of the force of the cannon- ball is inexact. I may also remark that the words " actual" and " potential" are in frequent use to qualify the state in which energy is met with. By actual energy is meant energy in an active state — energy which is doing work. By potential energy, energy at rest — energy capable of doing work, but not doing it. In a bent crossbow there is potential energy — energy in a state of rest, but ready to become actual, or to manifest itself when the trigger is pulled. Again, actual energy is evolved from the sun. By vegetable life this is made potential in the organic compounds formed. In these organic compounds the energy is stored up in a latent condition ; potential energy is reconverted into actual energy when they undergo oxidation during combustion or in their utilisation in the animal economy. The doctrine of the " Conservation of Energy" implies that energy is as indestructible as matter, that a fixed amount exists in the universe, and that, however variously it may be modified, transferred, or transformed — in spite of all the changes of which it may be the subject throughout the realm of nature — it cannot be created or annihilated, increased or diminished. The doctrine further implies that the different forms of energy have their definite reciprocal equivalents ; that so much chemical energy, for instance, will produce so much heat, which is the representative of so much motive power, and so on. The ascertained equivalents of heat and motive power have been already given. Accepted as applicable to the physical forces, the doctrine of the " Conservation of Energy" next began to be applied to living nature. Grove in his " Correlation of Physical Forces" (second edition, p. 89), suggested that the same principles and mode of reasoning adopted in his essay might answer equally for the organic as for the inorganic world, and that muscular force, animal and vegetable heat, &c, might, and one day would, be shown to possess similar defi- 4 INTKODUCTOBY REMAEKS. nite correlations. He proceeded no further/however, remark- ing that he purposely avoided entering upon a subject not pertaining to 'his own field of science. At this time the general belief prevailed that the processes going on in the living body were determined by " vitality'" or the " vital principle." The physical forces, it was sup- posed, were overruled in the living by the .vital principle. Without discussing whether we are to admit or deny the existence of this principle as a distinct operating force — a question which has been handled by some of the leading men of science of the day — we must, I think, concede, as a matter of experience, that in the living organism there are influences at play which have no existence in the dead matter around. Matter which has been impressed with life can pro- duce effects which dead matter cannot. This does not con- flict with the extension of the law of the " Conservation of Energy" to living nature. The effects produced may have their origin in the physical forces — the living matter forming the medium through which they operate. With artificial appliances force may be made to produce various effects, according to the nature of the instrument employed. With the same force in operation different kinds of work are per- formed, according to the character of the machine set i»j motion. Between the two — living matter and a machine-^ there exists an analogy which admits of being followed still further. It is only when in a certain state that matter is capable of forming the medium for the exercise of force in the production of living operations. Modify this state, and tliough there may be the same matter to deal with, yet it is no longer capable of fulfilling the same office it performed before. So, in the case* of an ordinary machine ; it must; possess a particular construction before it can form the medium for the operation of force. Disarrange this con- struction, and, although the matter remains unchanged, the- application of force is without its proper effect. Thus a dis- arranged machine may be compared with living matter devi- talised. In both, the capacity of being set in operation by force has existed, and in both that capacity has been lost/ Further, it may be said that a machine in working order but unoperated on by force— that is, in a state of rest — is like ON THE DYNAMIC RELATIONS OP POOD. 5 matter possessing vitality, but in a dormant state. Both are ready to move directly the proper force is applied. Applying the law of the "Conservation of Energy" to living nature, the forms of force which we observe in opera- tion are all primarily derived from the sun. "When a weight is lifted by the hand it certainly seems a long way off to go to the sun for the muscular force employed in the act ; yet the doctrine of the "Conservation of Energy" justifies, as I will proceed to show, the conclusion that its origin is there. To begin with, the force evolved in muscular action has its source in the material which has been supplied to the body in the form of food. Now, all food comes primarily from the vegetable kingdom, and vegetable products are built up through the agency of the sun's rays. It may be said that the energy contained in these rays, which has been employed in producing the compound, is fixed or rendered latent with- in it. "When the crossbow is bent, the force derived from the muscular action employed in bending it is stored up, ready to be again liberated when the trigger is pulled, no matter whether this be at once or a hundred years hence; and the force given to the arrow when it is launched is neither more nor less than that which has sprung from the muscular action employed in bending the bow. The same with vegetable products. Their formation is coincident with the disengagement of oxygen from oxidised principles and the development of combustible compounds. To effect this disengagement the operation of force is required. Now, the force so employed has its source in the heat and light evolved from the sun, and that which is used for the purpose may be said to become fixed and to exist in a latent condition— to exist stored up in the product, ready to be again liberated on exposure to conditions favorable to oxidation. Thus may these vegetable products be compared to a bent crossbow, containing as they do a store of latent force, which may for an indefinite period remain as such, or may be liberated soon after it has been fixed. Whenever liberated, it is no more nor less than the equivalent of the force which has been used in the formation of the product. Our coal-fields represent a vast magazine of force drawn, ages ago, from the sun's rays, 6 INTRODUCTORY REMARKS. and capable at any moment of being set free by the occur- rence of oxidation. Vegetable products, then, maybe regarded as containing a store of force accumulated from the vast supply continually emitted with the sun's rays ; and, upon the principle of in- destructibility enunciated, the force which has been employed in unlocking the elements in the combinations from which vegetable products are built up, and in forming the new com- pound, is contained in such compound in a latent state. Now, as above stated, animals either directly or indirectly subsist upon these vegetable products, and are thence supplied by them with accumulated force. By oxidation the force is set free in an active state under some form of manifestation or other. It matters not in what way — whether rapidly or slowly, or under what circumstances — whether inside or out- side the living system, the oxidation occurs ; the result is the same, as far as the amount of the force liberated is concerned, it being implied in the doctrine of the " Conservation of Energy " that it should constitute the equivalent of the solar force originally made use of. This is presuming complete oxidation to occur ; but in the processes of animal life, although fully oxidised compounds, like carbonic acid and water, are formed and discharged, yet others, like urea, are expelled in an imperfectly oxidised state, and carry with them a certain amount of latent or unutilised force. Thus it is that the various forms of force manifested in the actions of animal life trace their origin to that emitted from the sun. Plants are media for fixing solar force — for con- verting actual into latent or potential energy. Animals re- convert latent into various forms of actual force. Thus, in the various forms of actual force liberated by the actions of animal life, we have the equivalent of that which has been fixed by plants from the sun. As there is a revolution of matter, so is there a revolution of force within and around us. In the liberation of actual force a complete analogy may be traced between the animal system and a steam-engine. Both are media for the conversion of latent into actual force. In the animal system, combustible material is supplied under the form of the various kinds of food, and oxygen is taken in by the process of respiration. From the chemical energy due to ON THE DYNAMIC RELATIONS OF FOOD. 7 the combination of these, force is liberated in an active state ; and, besides manifesting itself as heat, and in other ways peculiar to the animal system, is capable of performing mechanical work. The steam-engine is supplied with combus- tible material under the form of coal, which differs from our food in representing the result of the vegetative activity of a former instead of the present epoch. Air is also supplied, and from the combination which occurs between its oxygen and the elements of the combustible material, heat is pro- duced, which in part is dissipated as such, but in part is ap- plied to the performance of mechanical work. According to Helmholtz, the animal economy, in respect of its capacity to turn force to account in the accomplishment of mechanical work, is a more perfect instrument than the steam-engine. His calculations lead him to conclude that whilst in the best steam-engine only one tenth of the force liberated by the combustion of its fuel is realisable as mechanical work, the rest escaping as heat, the human body is capable of turning one fifth of the power of its food into the equivalent of work. There is this, however, to be remarked, that the fuel of a steam-engine is a far less expensive article than the food of an animal being. The animal body, then, may be regarded as holding an analogous position to a machine, in which a transmutation of chemical into other forms of force is taking place. Food on the one hand, and air on the other, are the factors concerned in the chemical action that occurs. It is through the inter- play of changes between food and air that the manifestations of animal life, consisting of heat-production, muscular con- traction, nervous (including mental) action, and nutritive or formative, secretory, and assimilative action arise. The egesta, or substances dismissed from the system, are metamorphosed products of the ingesta, or substances entering the system. The elements are the same, in nature and in quantity, in the two cases, but their forms of combination, and, with them, their force accompaniment, are different. The force employed in building up the organic compounds belonging to food is again evolved as they descend by oxidation into more simple combinations, and in the force evolved we have the represen- tative of the active manifestations of animal life. If the pro- 8 ON THE DYNAMIC KELATIONS OF FOOD. ducts discharged from the system were fully oxidised prin- ciples, the force developed in the body would equal that con- tained in a latent condition in the food. Such, however, is not completely the case, a certain amount of latent force remaining, as has already been remarked, in some of the egesta. The position, therefore, may be formulated thus : — The latent or potential force of ingesta equals the force de- veloped in the body plus the force escaping with the egesta. In other words, the unexpended force in the egesta and the force disengaged by the operations of life, and manifested under the various forms of vital activity, equal the force con- tained in the ingesta. "What is required in food is matter that is susceptible of undergoing change in the system under the influence of the presence of oxygen. Life implies change, and the manifes- tations of life are due to the reaction of food, with the deriva- tives from it, and air upon each other. "While in the inorganic kingdom a tendency to a state of rest prevails' — while the closest affinities tend to become satisfied, and so establish equilibrium, in a manifestly living body rest is impossible. It is true, living organisms of certain kinds may exist in a state of rest, but then there is a suspension of vital manifes- tations. The state constitutes that which falls under the denomination of " dormant vitality." Animal organisms may exist in it, and the seed of a plant naturally remains for a while in it. Molecular rest, and, with it, an absence of any show of vital activity prevail. Concurrently, however, with the manifestation of vital activity, molecular change — change in a particular or prescribed direction — occurs. Organic compounds*; become resolved by the agency of oxygen into more simple combinations, as carbonic acid, water, and urea, and cease to be any longer of service. To maintain a continuance of vital activity fresh organic material is required ; hence the demand for food. But food and the other material factor of life oxygen — do not constitute all that is needed. It is further necessary that the two should be brought within the sphere of influence of living matter, in order that the changes may be made to pursue the particular line of direction resulting in the phenomena of life. ON THE ORIGINATION OF FOOD. Oub food is in the first instance derived from the vegetable kingdom. Dumas at one time said, "L'animal s'assimile done ou detruit des matieres organiques tontes faites ; il n'en cree done pas." But, as he afterwards admitted, this is not the case. The animal, it is true, is constantly consuming or destroying organic substances, and is incapable of forming them from the inorganic principles, but supplied with organic matter, organic compounds of various kinds are constructed. Mulder's discoveries in 1838 led up to the doctrine that the albuminous compounds of plants and animals agree in composition and properties, whence it was inferred that the animal simply took the compound produced by the plant and made it a component part of its own body. Liebig was the first to maintain that animals possessed the power of forming one kind of organic compound out of another. A warm con- troversy was at one time carried on upon this point, turning particularly upon the formation of fat. While, on the one hand, it was held by Liebig that, in the animal system, fat could be formed from sugar, Dumas and Boussingault main- tained, on the other, that whatever fat was found in an animal being was derived through its food from without. From the researches initiated by this dispute it became in- contestably established that Liebig was right, and the French chemists were ultimately compelled, even on the evidence of the results obtained by themselves, to abandon the doctrine they had advanced. A moment's consideration will, further, suffice to show that one kind of albuminous compound is capable of being con- structed from others. In the young mammal subsisting solely on milk, it is to the caseine that we must look for the source of fibrine and albumen ; and in the animal feeder, secreting 10 ORIGINATION OP BOOD. milk, the caserne produced is derived from the fibrine and albumen. Gelatine, moreover, has no existence in vegetable food. At the present day we may waive the discussion of this matter, it being now established that none of these nitro- genous principles enter the system under the form in which they occur in food. They are all converted, during the per- formance of digestion, into a certain principle (albuminose),, which is the principle that is absorbed, and that is subse- quently transformed by the assimilative power of the animal into the various compounds met with. The position, then, is this, that animals are not simply con- sumers of organic compounds, but are capable of exerting a constructive action as well. They must, however, be supplied with organic matter previously formed, and thus the capacity that really exists is that of transforming one organic com- pound into another. All organic matter has its primary source in the vegetable kingdom, from which kingdom, it follows, all our food must directly or indirectly be derived. The vegetable feeder goes directly for its food to the vegetable kingdom. The animal feeder is equally dependent upon the products of the vegetable kingdom for its pabulum. But it obtains it only at second hand, so to speak, or in an indirect manner, its food consisting of the flesh of animals which have themselves been nourished upon vegetable products. Now, it is only under exposure to the action of the sun's rays that plants will grow, and hence it is to the influence of these rays that we must refer the production of food in the first instance, and the primary source of all life upon our earth. It has already been shown how the energy emitted from the sun, under the forms of heat and light, is capable, through the medium of the plant, of disengaging oxygen from its combination with carbon and hydrogen in carbonic acid and water, and leading to the formation of re-oxidisable com- pounds ; and how the energy evolved from the re-oxidation of these compounds, whether by combustion or within the animal system, represents or forms the equivalent of that employed in effecting their construction. What an immeasurable amount of force to be, and to have been, emitted from the solar centre ! It is true that it must possess a store of heat altogether unrealisable by comparison INFLUENCE OP THE SOLAR FOECE. 11 with anything cognisable around us ; for it has been shown by recent investigations with the spectroscope that iron and other metals, which cannot by any known method of heat application be converted into the gaseous state upon our earth, exist in that state around the sun. It is true, also, that the sun is a body of almost inconceivable magnitude. To give the simile of Helmholtz, 1 " its diameter is so great that if you suppose the earth to be put into the centre of the sun, the sun itself being like a hollow sphere, and the moon going about the earth, there would be a space of more than 200,000 miles around the orbit of the moon lying all interior to the surface of the sun." But when we come to consider that, taking the view now held by philosophers, in that small pencil of rays which has impinged upon our earth at a distance of nearly 95,000,000 miles from the sun has been contained all the energy or source of power which has been fixed by plants, and much besides which has escaped being so utilised, we cannot help being struck at the immensity of the store of power existing in the sun. Geology teaches us that at an early epoch in the history of our globe this solar influence must have manifested itself to a much stronger degree than it does even at the present time. The vast coal-beds forming a portion of the earth's crust have originated in vegetable growth. During the carboniferous era, which comprises the period of this coal-formation, the atmosphere was probably laden with carbonic acid and humidity to a much greater extent than at the present day. But it is to the solar energy that we must look for the source of the luxuriant vegetation which evidently flourished at that time, and which must have existed in the arctic regions as well as in the lower latitudes, since coal-deposits are there found. It has been already stated that it is only under the influence of the force contained in the sun's rays that organic com- pounds are built up by the agency of the plant ; and it is found to be the green parts only of plants — those where chloro- phyll existes — that effect the decomposition of carbonic acid and water— fixing the carbon and hydrogen and liberating the oxygen. This operation, it is the distinctive function of the 1 "Lectures on the Conservation of Energy," 'Medical Times and Gazette,' 1864, vol. i, p. 415. 12 ORIGINATION OF POOD. plant to perform, and it fails to be carried on when either the influence of light is absent or chlorophyll is not present. Under these conditions — absence of light and chlorophyll — oxygen is absorbed and carbonic acid liberated instead, just as occurs in the animal. I have been informed that it is known to florists, as the result of practical observation, that in the case of the variegated-leaved geranium, a slip that may happen to be possessed of white leaves only will not grow alone like other slips. The absence of chlorophyll explains the non- capacity to effect the changes necessary for growth. The solar- beam is composed of rays possessing different • properties and different degrees of refrangibility, and the question has been raised — What part of the solar spectrum exerts greatest power over vegetable growth ? The coloured rays produced by passing a pencil of light through a prism are arranged in the following order : Violet, Indigo, Blue, Green, Yellow, Orange, Eed. The greatest illuminating power of the spectrum is in the bright yellow rays, and the greatest heating power in rays below the red, and therefore less refrangible than any of the coloured rays ; whilst the greatest chemical power — power of effecting chemical change — is in the rays at the other ex- tremity of the spectrum, namely, the violet, and in the invisible rays just above, where the highest degree is en- countered. Draper, from experiments conducted in 1843, states that on causing plants to effect the decomposition of carbonic acid in the prismatic spectrum, he found the yellow rays by far the most effective. The relative power of the various coloured rays he asserts to have been as follows : Yellow, Green, ACTION OF VEGETABLE LIFE. 13 Orange, Red, Blue, Indigo, Violet. In opposition to the conclusion arrived at by Draper, it is affirmed by others that it is to the blue and violet rays that must be referred the maximum power of effecting the decom- position of carbonic acid through the medium of the plant. Helmholtz 1 says : " The observations upon vegetable life have shown that plants can grow only under the influence of solar light, and that as long as solar light, and principally the more refrangible parts of solar light, the blue and violet rays, fall upon the green parts of plants, the plants take in carbonic acid and exhale oxygen." He further remarks that in exert- ing this influence these rays are completely absorbed ; for it can be shown that solar light which has passed through green leaves in full development is no longer capable of exerting any chemical influence. I have spoken of light as a factor in the construction of organic compounds by the plant. The elements of which these organic compounds consist are drawn from the inor- ganic kingdom, and chiefly, as Liebig pointed out, from carbonic acid, water, and ammonia — principles which all exist to a greater or less extent in the atmosphere, and from the atmosphere are to a large extent, if not entirely derived. In the case of the low vegetable organisms which become developed in moist situations as a green layer on the barren surface of rocks and stones, the elements required for their growth must have been derived solely from the atmosphere. In the case of the higher organisms, however, the elements of growth are drawn from the soil as well as the atmosphere. Humus, which forms the constituent of the soil which supplies these elements, consists of the decaying remains of organic products. But it is not as organic matter that humus serves as food to the plant ; that is, it is not the organic matter itself that is utilised. It is, on the other hand, as a source i " Lectures on the Conservation of Energy," ' Med. Times and Gazette/ , , 1864, vol. i, p. 473. 14 ORIGINATION OF FOOD. of carbonic acid and ammonia, principles resulting from its decomposition, that it owes its position in relation to the alimentation of plants. The stages passed through in the history of vegetable life leading to the provision of a fitting supply of food for animal existence may be thus represented :— Beginning, let us say, with a barren surface of rock, which may have been freshly exposed to the atmosphere from some subterranean, volcanic, or other agency, the germs of low vegetable organisms settling upon it, extract from the atmosphere their elements of growth. Passing through their term of life they die, and fresh ones spring up and similarly live and die. So the process goes on, higher and higher forms making their ap- pearance. The decaying remains of this primitive growth encrust what was a barren surface with a layer of earth or mould, in which ultimately the highest plants find a suitable position for taking root and growing. Thus clothed with vegetation, a fit locality is provided for the support of animal life, animal beings finding in the vegetable, products now existing the necessary material for their subsistence. It may be mentioned here that there is one class of vege- table organisms — the Fungi— which seems to occupy an ex- ceptional position, and to resemble animals in being dependent upon organic products for their growth. It is possible, how- ever, that the seeming appropriation of organic matter may be more apparent than real, and that the dependence upon organic matter may arise from a specially large and constant supply of carbonic acid and ammonia being required as a condition of growth. Still, it must be said that these vege- table organisms are not dependent for growth upon light like others, that they have no green surfaces for decomposing carbonic acid, and, in fact, that, instead of absorbing carbonic acid and setting free oxygen, they agree with animals in doing precisely the reverse. Such circumstances, it is true, are strongly suggestive of the occurrence of growth from an appropriation of organic compounds ; but there is this to be remarked, that the growth under consideration occurs only where decay is going on, and there is nothing, at all events, to show that any other than organic compounds in a state of decomposition can be made use of. ACTION OF VEGETABLE LIFE. 15 There are other vegetable organisms, such as Venus' fly- trap, the pitcher-plants, &c, which capture insects apparently with the view of deriving from their bodies organic matter for appropriation to the purposes of nutrition. In other respects, however, these plants agree in their mode of life with their fellow organisms. The. chief elements of the various organic compounds built up by the agency of vegetable life are, carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorus ; and the fol- lowing may be regarded as the sources from which they are derived. In the above enumeration carbon is mentioned first as being the element which occurs by far the most extensively in organic nature. Large as is the quantity of carbon entering into the composition of organic substances, the main, if not the entire source from which it is derived is the car- bonic acid in the atmosphere. According, however, to Saussure, the amount of carbonic acid contained in air is not, as a mean, more than one part, by volume, in two thousand ; but then it must be remembered that it is constantly being generated, not only as a product of animal life, but from various processes carried on around us. Now, it appears that the leaves and other green parts of plants are continually absorbing the carbonic acid, and, with the aid of light, effecting its decomposition, the oxygen being exhaled and the carbon detained and applied to the. production of organic substances. Whilst it is only by the leaves and green surfaces that carbonic acid is decomposed and oxygen liberated, it is probable that its absorption is not limited to those parts, but that some enters through the roots, this being derived from the process of decomposition going on in the organic matter of the soil, and from the carbonic acid carried down from the atmosphere with the rain. Striking as it may seem, yet there are sufficient grounds, for believing that the vast store of carbon contained in forests, of whatever extent we may encounter, has been derived in : the manner above mentioned. Geological investigations render it almost certain that at one time the atmosphere was far richer in carbonic acid than it is now, and that vegetation also was proportionately more luxuriant. 16 OEISINATION OF FOOD. The absorption of carbonic acid and exhalation of oxygen which take place in plants under the influence of light con- stitutes, then, a process of alimentation. The reverse process —the absorption of oxygen and exhalation of carbonic acid— a process which forms one of the principal phenomena of animal life — occurs also to some extent in plants, and stands out unconcealed during the night, when from the absence of light there is no decomposition of carbonic acid and libera- tion of oxygen going on. It also occurs as the result of certain operations of plant life, as, for instance, during germi- nation, flowering, and fruiting. Hydrogen and oxygen are supplied to an unlimited extent to plants under the form of water. In the production of the carbohydrate group of organic compounds ; that is, com- pounds such as starch, sugar, dextrine, gum, cellulose, &c, in which carbon is united with hydrogen and oxygen in the proportion to form water, it is possible that water is directly assimilated, although this is by no means an ascertained fact. In a large number of other compounds, however, it is evident from their composition that for water to serve for their pro- duction, its elements must undergo separation. The oleagi- nous compounds, for instance, chiefly consist of carbon and hydrogen'. The amount of oxygen present -is very much less than that required to form water with their hydrogen. For this element to be appropriated a deoxidation must occur, and it is believed that some of the oxygen exhaled by the plant under the influence of light has its source, not only in carbonic acid, but likewise in water. Although plants are freely surrounded with nitrogen — this element forming the large constituent it does of the atmo- sphere, yet it is not from the atmosphere that the nitrogen of organic matter is derived. The researches of Saussure and Boussingault have demonstrated that plants are incapable of appropriating the free nitrogen of the atmosphere and elaborating it into organic matter. Liebig's view, and it is one which is by common consent endorsed, is that the nitrogen of organic matter is derived from ammonia. This able chemist was the first to show that ammonia is a constant constituent of the atmosphere. It is true that the quantity in which it is present is so small that it cannot be recognised FORMATION OF ORGANIC COMPOUNDS. 17 except by abstraction from a large volume of air. It may be removed and its quantity determined (" On the Estima- tion of Ammonia in Atmospheric Air," by Horace T. Brown, ' Proceedings of the Eoyal Society/ vol. xviii, p. 286) by passing a given volume of air through water slightly acidu- lated with sulphuric acid. It is also susceptible of recog- nition in rain water, where it exists under the form of carbonate. Ammonia, like carbonic acid, forms a product of the decomposition of organic matter. The nitrogen of organic matter, indeed, is returned to the inorganic king- dom under the form of ammonia. Thus in humus we have a source of ammonia which, doubtless, combines with some of the carbonic acid also generated, and in this state. is in great part dissipated into the atmosphere. The great volatility of the product would lead to this result. Diffused through the atmosphere, it would be abstracted by rain and snow, and in this way carried back to the earth, to be brought in contact with the roots of plants, through which its absorption is supposed to be effected. According to Liebig, ammonia enters the vegetable organism in combination with carbonic or sulphuric acid, while, according to Mulder, the combination is with the acids he describes as existing in humus. Nitrogen is an element of the highest importance in regard to vegetable as well as to animal life. It is not only neces- .sary that it should enter into the constitution of vegetable substances so that animals may obtain a supply of it with their food, but it forms an indispensable element in relation to the molecular changes of the plant as well as of the animal. Wherever living changes are carried on nitrogenized matter is present. The proclivity of this to change forms one of its most characteristic qualities, and the changes it undergoes induce changes of a definite kind in other matter which per se has a tendency to remain at rest. Thus, in nitrogenized matter we have, as it were, the requisite starting-point for the various changes which result in the phenomena of life. The four elements which have been referred to, viz. car- bon, hydrogen, oxygen, and nitrogen, form by far the chief constituents of organic compounds, but sulphur and phos- phorus are also present, to a small extent, bound up with the 18 OEIGINATION OP FOOD. other elements in certain organic principles. Sulphur, for example, is met with in caseine, and both sulphur and phos- phorus in fibrine and albumen. The probable sources of these elements are sulphates and phosphates, the acids of the salts undergoing deoxidation through the medium of the opera- tions carried on in the plant, in the same manner as occurs in the case of carbonic acid. As yet I have been referring merely to the source of the elements entering into the constitution of the organic com- pounds produced by plants, and upon this point it may be considered that our information is pretty definite. The pre- cise mode, however, in which these elements are combined or elaborated into the infinite variety of organic compounds existing is quite another matter, and one which (it must be conceded) belongs as yet only to the domain of hypothesis. The point has been the subject of many laborious researches, conducted by some of the most distinguished observers, but, in spite of these attempts to elucidate it, we have at present little or nothing beyond conjecture to deal with. It may be fairly surmised, however, that the production of the higher compounds is effected step by step, or by a series of transition stages, and not by a direct or immediate union of the ele- ments entering into their composition. Whatever the exact changes that ensue, there can be no doubt that they proceed in a definite and precise order. In organic nature we know« that change induces change, and the change first set in motion in the act of growth may be regarded as starting the changes which produce the various organic compounds met with. Bodies in contact with changing matter are within the sphere of influence of a metabolic or metamorphosing force, and to the operation of this force is to be ascribed much that occurs as the result of living action. It is the formation of organic compounds which constitutes the special province of the plant to effect in relation to the production of food. Food, however, to fulfil the require- ments of animal life must contain certain mineral or inorganic as well as organic principles — a supply of the former being quite as indispensable as a supply of the latter. But we need not concern ourselves about a separate supply of mineral matter ; for, wisely, the productions of nature, contain in com- RESULTS OF ANIMAL AND VEGETABLE LIFE. 19 bination all that is wanted. It happens that, besides being furnished with carbonic acid, water, and ammonia for the formation of organic compounds, plants require for their growth a supply of saline principles. These they draw from the surrounding soil, and a portion of the advantage accruing to vegetable growth, from the employment of manure is owing to the mineral matter it contains, and which is thereby given to the soil. In appropriating mineral matter as an element of nutrition, the plant exercises a selective action. It is found, for in- stance, that some of the saline compounds belonging to the soil, and not others, are present, that they are present in different proportions as regards each other, and to a different extent in different parts of the plant. Mineral matter holds, in fact, a definite relation to the component parts of a plant, and probably enters into some sort of combination with the organic constituents. Thus, in vegetable products we find not only the organic, but likewise the inorganic matter we require ; and, in taking up and applying mineral matter as it does to its own pur- poses of growth as well as forming organic compounds, the vegetable organism contributes in a complete manner towards the supply of what is wanted for animal nutrition. A reciprocal relation, however, it must be observed, in reality exists between what is supplied and what is wanted. "We are as much adapted to the appropriation of the food supplied to us as our food is adapted to our wants. Were we not so adapted, existence would be impossible for us. In nature all things are mutually adapted to each other. In what has been said about the production of food by the vegetable kingdom for animal subsistence, it is seen that animals and plants stand in direct antagonism to each other, as regards the results of the main operations of life. Plants draw their food from the inorganic kingdom, and produce organic compounds. Animals find their food in these organic compounds, and, in applying them to the purposes of life, reconvert them into inorganic principles. In the appropria- tion of inorganic matter, as food, plants absorb carbonic acid and set free oxygen. Animals, in their consumption of organic matter, absorb oxygen and give out carbonic acid. 20 OEIGINATION OP FOOD. Thus, animal life and vegetable life stand in complemental relation to each other, and it is in accordance with the requirements for the persistence of living nature upon the surface of our planet that it should be so. If the operations of animal and vegetable life proceeded in one and the same direction only, the effect would be a gradual alteration of the chemical arrangement of matter, until a state of things was arrived at unfit for the further continuance of life. Under the existing order of things animals and plants in such a manner neutralise each other's effects upon surround- ing matter that they balance each other's operations, and thereby maintain a state of uniformity. THE CONSTITUENT ELEMENTS OF POOD. Of the various elements known to exist in nature only a limited number enter into the constitution of living bodies. The following is a list of those found as constituents of the human body. The first four, namely, carbon, hydrogen, oxygen, and nitrogen, exist in far larger quantity than any of the others. As for those which occur towards the end of the list, they are present only in exceedingly minute quan- tity, if, indeed, they are invariably present. It is more than doubtful if they are to be regarded as essential constituents. Carbon, Hydrogen, Oxygen, Nitrogen, Sulphur, Phosphorus, Chlorine, Sodium, Potassium, Calcium, Magnesium, Iron, Fluorine, Silicon, Manganese, Aluminium, Copper. ( The food being the source from which the elements form- ing the constituents of the body are derived, it follows that food must contain all the elements which are there met with. No article can, as food, satisfy the requirements of life that fails to comply with this condition. > ALIMBNTAEY PEINCIPLBS : THEIE CLASSIFICA- TION, CHEMICAL BELATIONS, DIGESTION, ASSIMILATION, AND PHYSIOLOGICAL .USES. Although it is necessary that our food should contain the elements that have been enumerated — and contain them in such proportion as to furnish the requisite amount of each to the system — yet it is not with these elements as such that, from an alimentary point of view, we have to deal. It is only in a state of combination that the elements are of any service to us as food ; and, as has been already mentioned, the com- bination must have been formed by the agency of a living organism — the combination must, in other words, constitute an organic product. Now, taking the different organic products which nature affords us as food, we find that they may, by analysis, be resolved into a variety of definite compounds. These con- stitute what are known as " alimentary principles," in con- tradistinction to " alimentary substances," or the articles of food as supplied to us by nature. In a scientific consideration of food it is necessary to speak first of the alimentary principles. It is only, indeed, by looking at it through its constituent principles that we are in a position to discuss its physiological bearings, and I will begin by pointing out the most convenient division and classi- fication to be adopted. Popularly, the ingesta are looked upon as consisting of food and drink, the one supplying us with solid, the other with liquid, matter. Superficially, this appears a natural and convenient mode of primary grouping, but in a physiological point of view it is completely worthless. " Pood " and "drink" constitute terms referring only to the particular CLASSIFICATION OF FOOD. 23 state in which an article for consumption may happen to exist — viz. whether it is in a solid or a liquid form. What is drunk, for instance, and this holds good particularly in the case of milk, may be rich in food or solid matter, and in the food we consume there is invariably a large proportion of liquid matter. Physiologically, then, the separation of the ingesta into " food " and " drink " is unsuitable. The two material factors of life are food and air ; and food may be considered as compris- ing that which contributes to the growth and nutrition of the body, and, by oxidation, to force-production. Regarded in this comprehensive light, food embraces both solid and liquid matter ; and the primary natural division is into organic and inorganic portions — that is, combinations of elements pro- ducible only through the agency of life ; and chemical combina- tions drawn simply from the mineral kingdom and incor- porated with the others. The inorganic portion of food consists of water and various saline principles. The organic portion may be subdivided into compounds of which nitrogen forms a constituent, and compounds from which it is absent ; in other words, into nitrogenised and non-nitrogenised compounds. The non- nitrogenised alimentary principles are composed of the three elements — carbon, oxygen, and hydrogen, variously united together, whilst the nitrogenised likewise contain these three elements, but, in addition, nitrogen} and, for the most part, sulphur, or sulphur and phosphorus as well. Liebig, regarding the nitrogenised and non-nitrogenised principles as contributing to quite distinct purposes in the animal economy, referred to them as forming the basis of a physiological classification. The former he looked upon as destined for appropriation towards the growth and main- tenance of the components of the body, and therefore he called them " plastic elements of nutrition." The latter he regarded as simply designed for undergoing oxidation, and, in this way, for serving as a source of heat. These he termed "elements of respiration," but the expression, it must be said, does not properly convey what is meant, and Dr. E. Dundas Thomson suggested that the term " calorifiant " should be employed instead. " Calorifacient," however, is a 24 ALIMENTARY PRINCIPLES. more appropriate word, and by general consent has been adopted. It stands to reason that for the growth and repair of the various textures of the body, as these have nitrogen forming an essential ingredient of their constitution, nitrogenised com- pounds must be supplied; but, from what is now known, it must also be said that these compounds are likewise suscep- tible of application to heat-production. They are truly, indeed, " histogenetic," or tissue-forming materials, but, by the separation of urea (which is known to occur in their metamorphosis in the animal system), a hydro-carbonaceous compound is left, which may be appropriated to heat-pro- duction. It may be asserted, in fact, that there is sufficient to show that the nitrogenised principles in reality subserve both purposes in the animal economy. In fat, again, we have a non-nitrogenous principle, and one belonging, therefore, to the calorifacient group. There is every reason, however, to believe that fat is essential to tissue- development. It seems to be intrinsically mixed up with nitrogenised matter in the animal textures. Certainly, it may be said to be directly applied towards the formation of adipose tissue. Fat, therefore, takes rank as a nutrient no less than as a calorifacient principle. Hence Liebig's definition is not to be accepted in a rigid sense. Although nitrogenised principles constitute true " elements of nutrition," yet it neither follows nor appears likely that they are limited to this purpose. Fats are un- doubtedly important calorifacient principles, and cannot per se supply what is required for tissue-development ; they, never- theless, take part in the process. According to our current views, which will be discussed more fully further on, fats are also concerned, in a manner not previously suspected, in muscular force-production. Taking all these considerations into account, Liebig's classification loses the scientific force it was originally supposed to possess. The subdivision of the organic portion of food, however, into nitrogenised and non- nitrogenised groups is still practically and physiologically convenient." Prout proposed a classification which arranged food in four CLASSIFICATION OP FOOD. 25 groups of principles, viz. (1) the aqueous, (2) the saccharine, (3) the oleaginous, and (4) the albuminous. It will be seen that this classification fails to include saline matter, which, as already said, forms an element indispensable to nutrition. The saccharine and oleaginous groups comprise non-nitrogenised principles, while the albuminous comprehends the nitrogenised. The classification that will be adopted in this Treatise is one which involves no expression of physiological destination, but is based on the chemical nature of the principles. It is first assumed that food falls naturally into — Organic, and Inorganic, divisions. Next, that the organic is subdivisible into — Nitrogenous, and Non-nitrogenous ; and further that the non-nitrogenous is naturally and .con- veniently again subdivisible into — Fats and Carbo-hydrates : the former consisting of carbon and hydrogen in combination with only a small amount of oxygen ; the latter of carbon with oxygen and hydrogen always in such relation to each other as to be in the exact proportion to form water. To this latter group belong such principles as starch, sugar, gum, &c. It must be observed that there are a few principles which do not strictly fall within either of the preceding groups. Such, for instance, as alcohol, the vegetable acids, and pectin or vegetable jelly. Alcohol occupies an intermediate place between the fats and carbo-hydrates, whilst the others are even more oxidised compounds than the carbo-hydrates — in other words, contain a larger amount of oxygen than is re- quired for the conversion of their hydrogen into water. These principles are hardly of sufficient importance, in an alimentary point of view, to call for their consideration under a distinct head, and they will therefore be spoken of in connection with the carbo-hydrates. 26 ALIMENTARY PRINCIPLES, Having said thus much upon the classification of the ali. mentary principles, I shall next speak of them in relation to their respective physiologioal bearings, taking the groups in the following order : 1. Nitrogenous principles, 2. Hydro-carbons or Fats. 3. Carbo-hydrates. 4. Inorganic materials. THE NITROGENOUS ALIMENTARY PRINCIPLES. Nitrogen enters largely into the composition of the animal body. It therefore requires to be freely snppbed from without. Although living in an atmosphere about four fifths of which consist of nitrogen, yet it is not from this source (though the question was formerly entertained) that our supply of nitrogen is drawn. Nitrogen, to be available for us, must be supplied in a state of combination. It is not, indeed, with nitrogen in the form of an element that we have anything to do in the question of alimentation, but only with compounds containing it, and such compounds, it may be said (as regards animal alimentation), that have been produced under the influence of life — that is, compounds which answer to the name of " organic." Organic nitrogenous matter, then, and not nitrogen, is what we require to have supplied to us, and what alone we have to deal with physiologically. Such nitrogenous matter must, therefore, constitute an essential ingredient of our food, and we find that it there exists under various chemical forms. Chemists recognise several well-defined compounds amongst the nitrogenous matter found in different articles of food. Besides these, there may be some nitrogenous matter which is still susceptible of being used, but which has not yet been specialised, and which in an analysis would fall amongst the extractives. This, however, cannot be sufficient in amount to be of much significance. If we look at the nitrogenised alimentary principles which have been made known, some are characterised by yielding proteine when subjected to the action of an alkali and heat, whilst from others, no proteine is similarly to be procured. 28 ALIMENTARY PRINCIPLES. The former comprise the albuminous group, and are often referred to as the proteine compounds ; the latter constitute the gelatinous principles. When the discovery of proteine was first of all made by Mulder the substance was regarded as forming the base or radical of the albuminous principles. It contains the four elements — carbon, hydrogen, oxygen, and nitrogen ,• and each of the albuminous principles was regarded as simply resulting from the combination of the supposed base with different quantities of sulphur and phosphorus, or sulphur only. It must be stated, however, that there is nothing to show that proteine really exists in the compounds from which it is to be obtained. It can be regarded only as a product of the chemical process to which it is necessary to subject the com- pounds in order to obtain it. Looked at in this light, it constitutes a chemical and not a physiological principle. It therefore has no direct physiological bearing, but nevertheless it serves to link together certain important physiological compounds. The albuminous or proteine compounds comprise albumen, fibrine, caseine, and certain other bodies which form modi- fications of these. Albumen may be looked upon as the most important repre- sentative of the proteine group. It consists of the four elements — carbon, oxygen, hydrogen, and nitrogen, with the addition of some sulphur and phosphorus. As it is met with in animal productions, it is in such intimate union with fatty, alkaline, and earthy matter, that it is with some diffi- culty separable from them. It varies to some extent in- its behaviour, as it is obtained from different sources. The albumen of the blood, for instance, does not agree in all respects with the albumen of the white of egg. One of the most striking properties of albumen is its coagulability upon the application of heat. It therefore exists under two states, viz. soluble and coagulated albumen. Albumen may be regarded as the pabulum in the blood from which the different animal tissues are evolved. That it can afford perse the nitrogenous matter required for nutrition is proved by its being the principle in the egg from which are developed the nitrogenous tissues of the chick. NITROGENOUS COMPOUNDS. 29 Fibrine is characterised by its property of undergoing spontaneous coagulation. It is composed of the same elements as albumen, but contains a larger proportionate amount of sulphur, and also a rather larger quantity of oxygen. Gaseine forms the proteine compound of milk. It is dis- tinguishable from fibrine by not undergoing spontaneous coagulation, and from albumen by not being coagulable by heat, and by being thrown down by organic acids which do not precipitate albumen. Besides the four elements — carbon, oxygen, hydrogen, and nitrogen — it contains sulphur, but no phosphorus. It is remarkable for the large quantity of phosphate of lime which it is capable of holding bound up with it, and the tenacity with which it retains it. There is, it should be stated, a little uncertainty regarding the chemical constitution of caseine. By some it is regarded, not as a simple, but as a compound body — a body composed (in reality) of a combination of two or more others. Besides these well-known proteine compounds there are modifications of them which have been particularised by chemists, and the following may be referred to as connected with the subject of food. Vitelline is the name given to the modified form of albumen which exists in the yolk of the egg. There are certain points in which this substance comports itself differently with re- agents from ordinary albumen. Globuline is the albuminoid matter existing in the fluid contents of the blood-corpuscle. It is there intimately asso- ciated with, but, nevertheless, quite distinct from, the colour- ing matter. The same principle is also found in the crystalline lens of the eye. Different opinions have been expressed regarding the true position it holds. Lecanu looked upon it as identical with albumen, and Simon with caseine, whilst Lehmann remarks that he would be disposed to place it by the side of vitelline, if the elementary analyses were not opposed to that view. Myosins constitutes the insoluble principle of muscular substance, and is obtained by subjecting the tissue in a finely divided state to repeated washings with water. Another substance was described by Liebig as constituting muscle fibrine, and was named by him syntonine. It forms the 30 ALIMENTARY PRINCIPLES. principle "dissolved from washed muscle by a weak solution of hydrochloric acid, and may be thrown down from this solution by neutralization with an alkali. It is present in and thereby increases the nutritive value of beef tea prepared according to Liebig's special directions. This principle has been lately regarded as nothing more than acid albumen; and it is said that if either albumen, myosine, vitelline, or fibrine be treated with dilute acids the formation of acid albumen occurs which is, or appears to be, identical with syntonine. The proteine compounds have as yet been referred to only as they occur in animal productions. But vegetable produc- tions also contain compounds which, in the language of Liebig, are not only similar to, but absolutely identical with, the albumen, fibrine, and caseine of the animal kingdom. Vegetable albumen is contained in wheat and the other seeds of the cerealia. The juices of most vegetables, such as tur- nips, carrots, cauliflower, cabbage, &c, yield more or less precipitate with heat by virtue of its presence. It is also found in considerable abundance in association with vegetable caseine in the oily seeds, such as almonds, nuts, &c. Vegetable fibrine, like albumen, is also found in the cereal seeds. It remains behind when flour is washed with a stream of water for the extraction of gluten. The albumen, starch, &c, are carried away with the water, and a tenacious mass is left, which is known as crude gluten. It is not this which constitutes vegetable fibrine, but vegetable fibrine forms a portion of it. By means of boiling alcohol the crude material obtained as above is resolved into two portions. The one which is dissolved consists of glutin and caseine, whilst that which remains is vegetable fibrine. Vegetable fibrine also exists in the juice of the grape and most vegetables. Vegetable caserne can be obtained from peas, beans, and other leguminous seeds, and is sometimes specially denomi- nated legumine. It also exists, with albumen, in the almond and such-like oily seeds. The gelatinous principles constitute nitrogenous compounds, but do not yield proteine like the compounds that have just been referred to. They comprise gelat/me and chondrine, and are obtainable only from animal products ; gelatine from. DIGESTION OP THE NITBOGENOTJS PBINCIPLES. 31 bone and other structures containing fibrous tissue, and cbondrine from cartilage. The most striking property they possess is that of their aqueous solution gelatinising upon cooling. It is gelatine which forms the basis of soups. Besides carbon, hydrogen, oxygen, and nitrogen, as consti- tuent elements, a small amount of sulphur appears also to be present. They contain no phosphorus. The question has been raised, and largely discussed, as to whether gelatine and chondrine exist in the tissues, or are formed in the process of obtaining them, viz. the prolonged boiling of the tissue in water. On looking at the chemical properties of gelatine, we notice that it forms an insoluble compound with tannic acid. Now, it is well known that a structure which yields gelatine, on being soaked in a solution of tannic acid, gives rise to the formation of the compound mentioned. It is this, indeed, which forms the basis of leather, a fact which is strongly in favour of gelatine really existing as a constituent of the animal body. It has been stated that the gelatinous principles which have fallen under consideration are to be obtained only from animal products. No nitrogenous compound of the kind is met with in vegetable materials. The jelly yielded by fruits and some other vegetable substances is quite a - different article. It oonsists only of the three elements:— carbon, hydrogen, and oxygen, and is known chemically as pectine and pectic acid. All the nitrogenous principles must undergo digestion before they can enter the system. Digestion, in fact, is simply a process which has for its object to fit substances for absorption into the system ; and the nitrogenous principles are in a state to resist absorption, certainly to any material extent, until they have been liquefied and transformed by the agency of digestion. Beyond being mechanically comminuted or reduced to a more or less finely divided state in the mouth, our nitro- genous food undergoes no change until it reaches the stomach. In this organ it is brought into contact with a secretion, the gastric juice, which has the effect of dissolving and trans- forming it into a principle which possesses the important 32 ALMENTAET PRINCIPLES. property of being highly diffusible, and thereby readily trans- missible from the alimentary canal into the blood-vesselB. With all the nitrogenous alimentary principles the result is the same. They each, under the influence of the. gastric juice, lose their characteristic properties and become con- verted into the highly soluble and diffusible product re- ferred to. Mialhe was the first to recognise this product of the digestion of the nitrogenous principles, and gave it the name of attmmmose. Peptone is the name which has since been applied to it by Lehmann. Mialhe held that the substance obtained by the digestion of the proteine bodies was identical with that obtained by the gelatinous principles. This would bring the latter into precisely the same position with regard to nutrition as the former. Although our knowledge about the precise extent of capacity of gelatine as an article of nutri- tion cannot be looked upon as complete, yet the information before us justifies the inference that it does not possess the same capabilities as an albuminoid substance. If such be true, the products of digestion of the two cannot be com- pletely identical, however much they may resemble each other in their general properties. It has been stated that, by the action of the stomach, the various principles composing our nitrogenous food lose their characteristic properties, and become converted into a sub- stance which has received the designation of peptone from one, and albuminose from another. Fibrine is dissolved, and is not susceptible of again solidifying. Albumen in a fluid form is not precipitated, as has been asserted, and then redissolved, but simply transformed. Albumen in the solid or coagulated state is dissolved, and fails to be again coagu- lable. Oaseine is first rendered solid, or curdled, and then redissolved. It is now no longer susceptible of being thrown down. Gelatine is liquefied, and cannot again be made to gelatinise. No matter from what principle a digestive product or pep- tone has been obtained, the following are the characters which are found to belong to it. It is soluble to the highest degree in water, and it signifies nothing whether the liquid is in the acid, neutral, or alkaline state. It is not preci- DIGESTION OF THE NITROGENOUS PRINCIPLES. 33 pitable from its aqueous solution by heat. It is soluble in dilute alcohol, but absolute alcohol precipitates it. It is an un- crystallizable substance, devoid of odour and almost of taste. In a physiological point of view its most important property is the high degree of diffusibHity it enjoys. It is designed for removal from the alimentary canal by absorption, and, by possessing the property referred to, a physically favorable disposition exists for the accomplishment of what is wanted. The nitrogenous alimentary principles, then, on reaching the stomach, are fitted for absorption by undergoing trans- formation into a highly soluble and diffusible substance. The change, we know, is wrought by the secretion of the stomach, although the precise modus operandi cannot be explained. There are two indispensable ingredients of the gastric juice, viz. pepsine (a neutral nitrogenized principle) and an aeid. Pepsine is a secretory product, peculiar to, and therefore obtainable only from, the stomach. About the acid there is nothing peculiar, and different views have been held regard- ing the kind of acid that is naturally present. With the combination of pepsine and acid a liquid is obtained which dissolves nitrogenous matter in the same manner out of as within the stomach. According to Lehmann, it is only hydrochloric and lactic acids — and these, the same authority affirms, give the acidity to the natural secretion — which yield an energetic digestive fluid with pepsine ; but, according to my own experiments on artificial digestion, other acids, such as the phosphoric, sulphuric, citric, and so on, will equally answer the purpose. From the above statements it follows that the solution of nitrogenous food in the stomach is effected by the action of a liquid which owes its virtue to the presence of a couple of principles— pepsine and an acid. The action of this liquid is favoured by the elevated temperature belonging to the body, and also by the movement to which the contents of the -stomach are subjected by the action of the muscular fibres with which the walls of the organ are provided. As it is reduced to a fluid state the food is forced on into the upper bowel. Chyme is what this product of gastric digestion is called Besides nitrogenous matter in a dissolved state, it contains a portion suspended in a finely divided form which 34 ALIMENTARY PKINCIPL1S. has not yet undergone solution, and likewise, in the same state, those constituents of the food which resist the solvent action of the stomach. The nitrogenous matter which has escaped from the stomach in an undissolved state is submitted to a further digestion in the intestine. This may be shown by direct experi- mental observation. And it is not by a continued action of the gastric juice which passes on with the food in its course, but by an action exerted by the secretions poured into the intestine itself. It has been stated that the presence of an acid forms an indispensable factor in gastric digestion. The chyme as it passes on from the stomach is strongly acid. It contains nitrogenous matter which has not yet undergone solution, and also gastric juice whose power (it may be in- ferred) has not become exhausted. So far, we have con- ditions which suffice for a continuance of the process carried on in the stomach. It happens, however, that on reaching the small intestine the chyme encounters alkaline secretions. The pancreatic juice is, to a marked extent, alkaline, and so is also the intestinal juice. The bile likewise contains a quantity of alkali in feeble combination, and easily taken by the gastric juice acid. Thus it happens that the chyme becomes more or less neutralised as the small intestine is being traversed. As the result of observation, in fact, I have noticed that by the time the lower part of the' ileum is reached the intestinal contents may be found to present a neutral or even alkaline reaction. In this way, through con- tact with the secretions poured into the intestine, the energy of the unexhausted gastric juice contained in the chyme is destroyed, and whatever solution of nitrogenous food now occurs must be due to another agency. Let us, therefore, inquire into the effect which the various secretions, as they become incorporated with the chyme, are capable of producing. First, as regards the intestinal juice. This fluid, it is evident, possesses some solvent influence upon nitrogenous matter. Bidder and Schmidt ascertained by experiment that meat and coagulated albumen contained in a muslin bag undergo, on being placed in the empty small intestine, in which the bile and pancreatic juice are prevented by a liga- ACTION OF PANCREATIVE JUICE. 35 ture from descending, in from four to six hours' time a con- siderable amount of digestion. In an experiment performed by myself, in which the hind legs of a frog that had been separated from the body, were introduced into the empty small intestine, secured by a ligature from the descent of secretions from above, I found, after the lapse of six hours, the legs partially digested — a portion of the skin, for example, having been dissolved away, the muscles underneath it sepa- rated, and some of the bones, to a slight extent, exposed. Next, as regards the pancreatic juice. Besides its other offices in the animal economy, this liquid acts upon and dis- solves nitrogenous matters as appears from the following con- siderations. In 1836, Purkinje and Pappenheim asserted that the pan- creas contained a principle capable of exerting a digestive action upon the nitrogenized elements of food. This state- ment attracted little attention, and soon dropped out of notice. More recently Lucien Corvisart, of Paris, having re-opened the subject, proved, by a series of experiments, that the pancreas, as one of its functions, supplements the action of the stomach, and, after a copious meal, contributes to digest those nitrogenous matters which have escaped the stomachic digestion. As far as the result is concerned, the two kinds of digestion, he states, coincide, each leading to the production of albuminose. While acidity, however, is a necessary condition to digestion in the case of the gastric juice, the pancreatic secretion, it is affirmed, possesses the power of acting equally well, whatever the existing reaction — whether acid, neutral, or alkaline. In support of his doctrine, Corvisart has adduced three sets of experimental results. In the first place : if the pancreas of an animal be taken when its active principle is at its maximum of quantity and quality, that is, from the fourth to the seventh hour after digestion has begun, and it be then finely cut up and infused for an hour in twice its volume of water at a temperature of 20° Cent. (68°Fahr.), and the infusion be at once experi- mented with, it will be found, he asserts, to possess a power of dissolving the nitrogenized alimentary principles, and con- verting them into albuminose ; and this, with no evidence of 36 ALIMENTARY PRINCIPLES. putrefaction being perceptible, provided the experiment be stopped at the end of four or five hours, in which time, under a temperature of about 100° Fahr., the pancreatic principle will have effected all that it is capable of doing. Secondly : the pancreatic juice obtained during life fromi the duct of the gland is found, he affirms, to be capable of actingas a powerful solvent on the nitrogenized alimentary principles, when the requisite, precautions are taken in conducting the- experiment j the juice, that is to say, must be obtained from the fourth to the seventh hour after the ingestion of food, at which time it is charged to its maximum degree with the pancreatic principle; and must also be experimented with immediately after its collection. It dissolves, Oorvisart says, fibrine more quickly and more largely than albumen. The heat being maintained between 42° and 45° Cent. (108° and 113° Fahr,), a specimen of pancreatic juice of ordinary energy dissolves, it is stated, if the mixture be agitated every quarter of an hour, all that it is capable of taking up — of fibrine in two or three hours at the most, and of solid albumen in four or five hours ; the experiment, up to this time, being attended with no evidence of ordinary decomposition, while, at a. sub- sequent period, ordinary decomposition is found to set in. Thirdly : nitrogenized substances introduced into the duor denum when pancreatic juice is flowing into it are found to be dissolved, notwithstanding the gastric juice and bile are, pre- cluded from entering by applying a ligature to the pylorus and bile-duct. It is necessary to. state that, the evidence derivable. from the last experiments must not be taken for more than it is. really worth, viewed in relation to pancreatic juice per se. The bile and the gastric juice may, it is true, have been prevented entering the duodenum, and thereby precluded from con- tributing to the effect, but it is impossible to exclude from operation the secretions of Brunner's and the other glands of the duodenum. My own experiments, with the pancreatic juice at first in- clined me to think that the effects, producible on nitrogenous:' matter through the agency of the pancreas were rather like, those which result from putrefaction than from true digestion. On re-performing the experiments, however, I obtained ACTION OF PANCREATIC JTJICI. 37 results which certainly appeared to indicate that some diges- tive action had been at work. For example, upon oper- ating with the pancreatic infusion, taken conformably with the instructions of Corvisart, I found that frogs' hind legs (which, according to my experience, constitute one of the most, if not the most, sensitive and distinct tests of digestive action) were, upon some occasions, softened, so that the flesh broke down under very Blight pressure, without any evidence of ordinary putrefaction being apparent. The effeot, however, was not to be compared with what is observed after the use of artificial gastric juice, and ordinary decomposition tends quickly to occur, which is not the case in experiments con- ducted with gastric juice. Whatever the power actually enjoyed by the pancreatic juice in this direction, the chief point of interest to us as re- gards the subject of food is not whether this or that secretion, poured into the intestine, will dispose of nitrogenous matter, but whether nitrogenous matter really undergoes digestion in the intestine ; and, thus framed, it will be presently seen that the question admits of being answered in a very positive manner. The bile forms another secretion, which becomes incorpor- ated with the alimentary matter after its exit from the stomach. There is nothing, however, to show that this fluid possesses any solvent power over the nitrogenized principles of food. Bemarks have been made upon the action of the secretions taken individually, but as regards the subject of food, the point of greatest interest to us, as has been already said, is what occurs within the intestine when all the secretions are allowed to enter. Experiment shows that there is a very powerful solvent action exerted, and, as I can state from personal investigation, a few hours suffice for nitrogenous matter, introduced directly into the upper part of the small" intestine, to be completely digested. With reference, there- fore, to the digestion of nitrogenous matter, the intestine may undoubtedly be regarded as performing a part supplementary to that of the stomach. Besides its other functions, it serves to complete the digestion of whatever nitrogenous alimentary matter may have escaped the digestive action of the stomach, and it may be remarked that the same result— namely, the 38 ALIMENTARY PRINCIPLES. production of albuminose or peptone — occurs as when the solution has been effected in the stomach. Eeviewing the stages that are passed through preliminary to the appropriation of nitrogenous matter within the system, we have seen that, through the agency of the stomach and of the intestine, it undergoes conversion into a principle which, from its diffusible nature, is readily susceptible of absorption, and it is in this form, viz. as albuminose, that the various nitrogenous alimentary principles reach the circulation. The conversion of the nitrogenous alimentary matters into albuminose is necessary, it is further to be remarked, not only as a process preparatory to absorption, but also as fitting them for subsequent application to their proper destination. It can- not absolutely be affirmed that no absorption whatever occurs without previous conversion into albuminose ; but this much is certain, that the amount so absorbed must be very trifling, and it can be shown that if they directly reach the circulation in any quantity they visibly pass off without being applied to the purposes of the economy. Bernard was the first to demonstrate that the albumen of egg, reaching the circulation without having previously under- gone digestion, quickly passes from the system into the urine. If introduced directly into one of the blood-vessels, or even if injected into the subcutaneous tissue, it rapidly betrays its presence in the urine. This I can attest from my own ex- perience. Both after injection into a vein and into the subcutaneous tissue the albumen of egg, as I have often seen, is soon recognisable in the urine. It has also been observed that a meal consisting largely of eggs, particularly if taken, after prolonged fasting, has been followed by the appearance of albumen in the urine. Here, apparently, it has happened that some albumen has reached the circulation without having undergone the usual conver- sion ; and, as when experimentally injected, has been thence discharged with the urine. Hence it may be concluded, not only that egg-albumen and blood-albumen differ strikingly from each other in a physiological point of view, but that egg- albumen, as such, is not fitted for entering the circulation. The conversion of albumen into albuminose, therefore, not only bears on the facility of absorption, but on the adaptability PRODUCTION OF ALBUMINOS1. 39 for subsequent application in the system. The process of metamorphosis, in fact, is required, not only with a view to adaptability for absorption, but to subsequent fitness for utili- sation in the system. Caseine and gelatine I have found 1 comport themselves in the same manner as albumen, namely, pass off from the system with the urine when directly introduced into the circulation. The injection of three ounces of milk into a vein was observed in an experiment to be followed by the appearance of caseine in the urine. The injection of 100 grains of isinglass, dis- solved in two and a half ounces of water, also so charged the urine with gelatine as to give rise to the formation of a firm, solid jelly on cooling. Thrown off as they thus are from the system, albumen, caseine, and gelatine are evidently not adapted for direct introduction into the circulation. Fibrine, on account of its solidity, cannot be similarly experimented with. Digestion, in its case also, is an indispensable condition to its introduction into the circulation. In respect, indeed, of all these prin- ciples, it may be said that their metamorphosis in the digestive system is needed as a preliminary step to their capability of appropriation in the body, and their application to the pur- poses of life. We have followed the nitrogenous alimentary principles to the stage of albuminose. The precise nature of what next ensues is not yet known. There can be little or no doubt as to the progress from albuminose to the albumen of the blood, but as to what next occurs we have no data to show. With the ultimate products that are formed we are acquainted, but the steps of metamorphosis are as yet beyond our knowledge. The chain we have hitherto followed now wants one or more links, which we have as yet no means of discovering. As regards the seat of metamorphosis we have also no information of a precise nature to deal with, but we may, nevertheless, hazard the surmise that the liver is the viscus in which albuminose, lite other nutritive matters absorbed from the alimentary canal, mainly, if not entirely, undergoes meta- * "Gulstonian Lectures (1862) on Assimilation and the Influence of its Defects on the Urine," ' Lancet,' 1863, vol. i, p. 574. 40 ALIMENTARY PRINCIPLES. morphosis. The various nitrogenous principles of the body- must be primarily derived from it ; but, whether by direct transformation into them, or by passing through the stage of albumen, we have not the means of deciding. That albumen is susceptible of metamorphosis, however, into the other prin- ciples, we know, from its forming in the egg the pabulum whence the various nitrogenous principles of the young bird take their origin. Instead of wandering farther into the domain of conjecture as to the subject of metamorphosis, let us now turn our attention to the purposes fulfilled by the nitrogenous prin- ciples as alimentary matter. Foremost in importance is the supply of material for the development — -primarily, a/iid for the renovation — secondarily, of the tissues. Wherever vital operations are going on, there nitrogenous matter is present, forming, so to speak, the spring of vital action. Although non-nitrpgenous matter contributes in certain ways towards the maintenance of life, yet it is nitrogenous matter which starts and keeps in motion the molecular changes which result in the phenomena of life. Nitrogenous matter, it may be said, forms the basis, without which no life manifests itself. Life is coincident with mole- cular change. In non-nitrogenous matter the elements of the molecule are not, of themselves, prone to change ; whereas in the molecule of nitrogenous matter there exists a greater complexity of grouping among the elements, and these cohere so loosely, or are so feebly combined, as to have a constant tendency to alter or to re-group themselves into simpler com- binations. By this change in the nitrogenous, change is induced in the contiguous non-nitrogenous molecule, and, occurring as the whole does in a definite or prescribed order, the phenomena of life are produced. Nitrogenous matter, in this way forming the instrument of living action, is inces- santly being disintegrated. Becoming thereby effete and useless, a fresh supply is needed to replace that which has fulfilled its office. The primary object of nitrogenous ali- mentary matter may thereupon be said to be the development and renovation of the living tissues. USES OF NITROGENOUS MATTER. 41 We have seen that nitrogenous matter forms an essential part of living structures. It holds the same position in the case of the secretions. These owe the active properties with which they are endowed, chiefly, if not entirely, to a nitro- genous constituent. This is drawn from the blood by the glands just as it is drawn by the tissues ; and on passing, from the blood it is modified or converted, by the agency of the gland, into the special principle encountered. Nitro- genous matter is thus as essential to the constitution of the active secretions as it is to the tissues ; and, as the amount of the secretions required is in relation to the general vital activity, a corresponding demand for nitrogenous matter is created. I now come to treat of nitrogenous matter in relation to force-production. The dependence of muscular and nervous action upon oxi- dation of the respective tissues is one of the many doctrines which have emanated from the inventive intellect of Liebig. According to the view propounded, nitrogenous matter alone constitutes the source of muscular and nervous power. The tissues being consumed in the exercise of their functional activity or the manifestation of their dynamic properties, fresh nitrogenous matter is alleged to be needed to replace that which has served for the production of power. Thus viewed, nitrogenous matter has been regarded as not only applied to nutrition and to the formation of the nitrogenous constituents of the active secretions, but also to the restitu- tion of the loss incurred by the production of power. What wonder, then, if, with all these purposes to fulfil, the nutritive value of food should have been measured, as it latterly has been, by the amount of nitrogenous matter it contains ? Liebig's doctrine was at once accepted, and until recently has been looked upon as expressing a scientific truth. Like many other of its author's views, its plausibility was such that no one ventured to question its soundness. Gradually, however, experimental inquiry began to invalidate it, and the reactionary move has advanced till Traube has been led to express himself in directly opposite terms regarding the source of muscular and nervous power. According to this 42 ALIMENTAEY PKINCIPLES. authority, for instance, the organized or nitrogenous part of a muscle is not destroyed or consumed in its action. The resulting force is affirmed to be due, instead, to the oxidation of non-nitrogenous matter — the muscle merely serving as a medium for the conversion of the generated force into motor power. The point has attracted much attention of late, and researches of an elaborate nature have been con- ducted with regard to it. Let us see the position in which these researches have placed it. The argument representing the question to be solved may be thus expressed :— Does the force evolved by muscular action proceed from destruction of muscular tissue ? If so, nitrogenous matter would be needed to replace the loss in- curred, and the result would be equivalent to nitrogenous matter through the medium of muscle being applied to the production of motor power. Now, if muscular action is coincident with the destruction of muscular tissue, there must, as a product of the destruction, be a nitrogen-con- taining principle eliminated. The elements of the compounds that have served their purpose in the economy do not accu- mulate, but are discharged from the system under certain known forms of combination. The nitrogen, therefore, be- longing to a consumed nitrogenous structure should be recog- nisable in the effete matters thrown off from the body. Nay, more ; as the force developed by muscular action cannot- arise spontaneously — as it can be produced only by transmutation from another force — the destruction of muscular tissue (which through the chemical action involved supplies the force) should be in proportion to the amount of muscular work performed, and the nitrogen contained in the excreta in proportion also to the amount of muscular tissue destroyed. Now, in proceeding to measure the extent of tissue meta- morphosis by the nitrogen eliminated, it is necessary, in the first instance, to be sure of our data regarding the channels through which nitrogen finds its exit from the body — it is necessary, that is to say, to ascertain whether nitrogen escapes with the breath and perspiration, as was at one time asserted, as well as by the alimentary canal and the kidneys. We have no accessible means, it must be stated, of determining in a direct way whether nitrogen passes off by the lungs and NITROGENOUS MATTER AND MUSCULAE ACTION. 43 skin. Our conclusions have to be based upon comparing the nitrogen ingested with that encountered in the urine and alvine evacuations. Formerly it was said that a deficiency in the latter existed, and it was put down to loss by pulmo- nary and cutaneous elimination. Barral, for instance, only detected half the nitrogen of the food in the urine and faeces, and thence inferred that the remainder was discharged with the breath and perspiration. In opposition to this, however, several trustworthy observers (amongst whom may be named Voit, Banke, Haughton, and Parkes) aided by the improved methods of analysis introduced by modern experience, have recovered within a very close approach all the nitrogen of the food from the urinary and intestinal excreta. Dr. Parkes J observations are especially worthy of reliance, and he confi- dently asserts that it may be looked upon as established that an amount of nitrogen is discharged by the kidney and intes- tine equivalent to that which enters with the food. Admitting this to be the case, we have only to look to the products that escape from these two channels for the information that is wanted about the discharged nitrogen in relation to the question before us. Next comes the determination of the relation respectively held by the urinary and intestinal nitrogen to the point under consideration. It has long been known that the chief portion of the escaping nitrogen is to be met with in the urine. Lehmann, for instance, found, while subsisting on a purely animal diet (eggs), that a daily average of 30-3 grammes (467 grains) of nitrogen entered his system, and that a daily average of 24"4 grammes (376 grains) was discharged by the urine. Here, therefore, it was ascertained that an amount equal to five sixths of the ingested nitrogen escaped by the kidneys. But more recent and precise evidence has been afforded by a series of very carefully conducted observations made upon two soldiers by Dr. Parkes. 1 The observations extended over sixteen consecutive days, and the results not only bear on the ingestion and egestion of nitrogen generally, but likewise show that the great bulk of out-going nitrogen is to be met with in the urine. The men were both of almost precisely the i 'Proceedings of the Royal Society,' June 20th, 1867. 44 ALIMENTARY PRINCIPLES. same weight at the end of the time as at the beginning, so that the in-going and out-going matter must have been closely balanced. They were subjected to varying conditions of rest and exercise, but consumed exactly the same allowance of food every day. The nitrogen in the food taken during the sixteen days amounted to 313 - 76 grammes; and, from the urine of one of the men (distinguished as S) there were recovered 303 - 660 grammes, and from that of the other (distinguished as B) 307*257 grammes. Thus, the amount of nitrogen discharged from the kidneys was, in the case of S, only about ten grammes, and in that of B, six grammes less than that admitted with the food. The alvine evacua- tions were collected and analysed only upon three occasions. Taking the mean of the results then obtained as representing the daily average, and calculating from this for the sixteen days, the quantity of nitrogen discharged from the bowels amounted in S to 25 - 8 grammes, and in B to 17"2 grammes, thus somewhat exceeding the difference between the ingested nitrogen and that excreted in the urine, or giving, in other words, rather more nitrogen discharged than nitrogen ingested. The nitrogen discharged from the bowels may be said to have been found to form, upon an average, from about one eighth to one twelfth or one thirteenth of the total nitrogen voided. Owing its origin, as it does, to the nitrogen belong- ing to the undigested food on the one hand, and that con- tained in the unabsorbed intestinal secretions on the other, it is constantly liable to incidental variation. There is this, also, to be remarked, that the nature of its source excludes it from possessing any relation to the question under con- sideration. We have, therefore, only the urinary excretion to look to as forming the channel through which the exit of nitrogen, resulting from the metamorphosis of nitrogenous matter in the system, takes place; and observation has shown that in the human subject it is mainly under the shape of urea that the escape occurs. What, now, is the state of the urine in relation to rest and exercise ? If muscular disintegration forms the source of mus- cular work, the quantity of urinary nitrogen ought to increase in proportion to the amount of muscular work performed. Lehmann, imbued with Liebig's views, as his writings MUSCULAR ACTION AND ELIMINATION OP NITROGEN. 45 show, speaks of there being an actual increase in the elimina- tion of urea in proportion to muscular exercise, and yet he gives it as the result of observation upon himself that, while under ordinary circumstances he passed about 32 grammes (493 grains) of urea in the twenty-four hours, the quantity passed after severe bodily exercise was upon one occasion 36 grammes (555 grains), and upon another 37'4 grammes (577 grains) — only this insignificant disparity to correspond with the difference in the amount of muscular work per- formed. Voit experimented upon a dog, and determined the amount of urea voided during rest and the performance of mechanical work, in association with abstinence and a regulated diet of meat. The work imposed upon the dog was running in a treadmill. The results, both during abstinence and feeding,, exhibited no -material excess in the urea voided during work over that voided during rest. Dr. E. Smith, also, in his observations on the elimination of carbonic acid and urea during rest and exercise, found, in the case of the prisoners at Coldbath Fields, that, in the absence of food, the labour of the treadwheel did not, to any material extent, increase the nitrogen discharged under the form of urea. Like others have done, he noticed a distinct relation between the urea discharged and the food ingested. At the same time he regarded — and this was several years ago, when our knowledge stood in a very different position from what it does now — the relation between the urea and muscular work as far less established then than it had been held to be for some time before. The theory that muscular work is dependent on, and pro- portioned to, the destruction of muscular tissue by oxidation, received its decisive blow from the now celebrated observa- tions of Drs. Pick and Wislicenus, professors of physiology and chemistry respectively at Zurich. 1 These experimen- talists subjected themselves to a measurable amount of work by ascending a mountain of an ascertained height. They argued that if the work performed be due to destruction of muscular tissue — seeing that the nitrogenous product of ' " On the Origin of Muscular Power," by Drs. Pick and Wislicenus, ' Philosophical Magazine * (Supplement), yoL xxxi, 1866. 46 ALIMENTARY PRINCIPLES. destruction is discharged in great part, if not entirely, with the urine — the collection of the urine, and the determination of. its nitrogenous contents, ought to show the amount of nitrogenous matter destroyed. Again, as the mechanical work to be performed must be represented by an equivalent of chemical action to produce it, the destruction of nitro- genous matter, as measured by the nitrogen appearing in the urine, ought to accord with the amount of work performed. To simplify the experiment, the food consumed by the expe- rimentalists consisted solely of non- nitrogenous matter; so that the nitrogen appearing in the urine might be derived exclusively from that belonging to the system. Drs. Pick and Wislicenus chose for ascent the Faulhorn near the lake of Brienz, in the Bernese Oberland, a steep mountain of about 2000 metres (6561 feet) above the level of the lake, and furnished with hotel accommodation on the summit, enabling them to rest over-night and make the descent next day. On the 30th of August, between 10 minutes past 5 in the morning and 20 minutes past 1 in the afternoon, the ascent was made. From the noon of the 29th no nitrogenous food had been eaten by the experimenters, their diet consisting solely of starch and fat (taken in the form of small cakes), and sugar — as solid matter; and tea, beer, and wine — as drink. After ascending the mountain, Drs. Pick and Wisli- cenus rested, and took no other kind of food till 7 in the evening, when they partook of a plentiful repast of meat and its usual accompaniments. They began to collect their urine for examination from 6 p.m. of the 29th— that is, six hours after the commence- ment of their non-nitrogenous diet. The urine secreted from this time till 10 minutes past 5 a.m. of the 30th, when the ascent began, was called the "before-work" urine. The urine secreted during the ascent was called the "work" urine; and that from 1.20 p.m. to 7 p.m. (from the comple- tion of the ascent to the cessation of the non-nitrogenous diet) the "after-work" urine. Finally, the urine secreted during the night spent on the Paulhorn up to half -past 5 a.m. was also collected, and denominated "night" urine. Bach specimen was measured, and both the quantity of Fick. Wislicenus, Grammes. Grammes. . 0-63 . . 0-61 . 0-41 . . 039 . 040 . . 040 . 045 . . 0-51 FICK AND WISLICENUS' EXPERIMENTS. 47 urea and the absolute amount of nitrogen contained in it determined. For the object before us it will suffice to con- fine our attention to the nitrogen ; and the quantity of this element secreted per hour (calculated from the amount con- tained in the respective specimens and the time passed in secretion), stood thus, for the several periods : Quantity of Nitrogen excreted per hour. Before work During work After work Night A glance at these figures shows the agreement that existed in the two cases. The result proved that, whilst the nitro- genous excretion was related to the food ingested, it was not so to muscular action. Less nitrogen, it is noticeable, was voided during the "work" and "after- work" than during the " before-work" period, and this was plainly attributable to the absence of nitrogenous food from the diet. During the night, after the meal of mixed food, there was an increase, greater in Wislicenus's than in Pick's case ; but the one meal did not bring the amount of nitrogen up to the point at which it stood shortly after the commencement of their abstinence from nitrogenous food. The conclusion, then, that in the first place may be drawn from this experiment is that muscular work is not accom- panied by the increased elimination of nitrogen that might be looked for if it resulted from the oxidation of muscle. But let us inquire whether the disintegration of nitrogenous matter which actually occurred during the " work" and " after- work " periods, as measured by the nitrogen excreted, would account for the generation of an amount of force equi- valent to that expended in the work performed. Knowing that the nitrogenous matter of muscle contains — say, in round numbers — 15 per cent, of nitrogen, it is easy to calculate to how much muscular tissue the excreted nitrogen was equivalent; and taking the muscular tissue thus repre- 48v ALIMENTARY PRINCIPLES. sented, an approximate, if not an absolute, estimate can be given of the amount of mechanical work which its oxidation would be capable of performing. The height of the ascended mountain, likewise, being known, the amount of muscular force actually employed in raising the weight of the body to the summit can also, be definitely expressed. We have, therefore, these data supplied : 1st. From the nitrogen excreted the amount of nitrogenous matter oxidized; 2nd. The amount of force that this oxidation would gene- rate; and — 3rd. The expenditure of force required to raise the bodies of the experimenters to the height they reached. Now, if the work performed were due to the oxidation of muscle, the second factor ought to equal the third ; that is, the force producible from the muscle oxidized ought to be equivalent to the force that was expended. The results of the calculation however show, as will be presently seen, that the force expended considerably exceeded the amount derivable from the nitrogenous matter consumed. Nor is this all. Besides the force expended in simply raising the body-weights of the two men to the elevation reached, there would also, be occurring, during the per- formance of the work, an expenditure of muscular power in keeping up the circulation, in respiratory action, and the other life-processes. The calculations on these points have been carefully worked out by Fick and Wislicenus; and though the data for the process are scarcely precise enough to warrant our regarding the results as scientifically exact, still, they may be admitted as affording a basis for a safe general conclusion to be drawn. We are also told that wherever a doubt existed about the data, figures were taken as favorable as was allowable to the old hypothesis, which referred the source of power to muscular oxidation. In giving the. conclusion furnished, it is not necessary to, introduce the details of the calculation. It will suffice to say that summarily stated the result of the calculation showed that the measured work performed during the ascent exceeded by about one half in Fick's case, and more than three fourths MUSCULAE WORK AND MUSCLE OXIDATION. 49 in that of Wislicenus, the amount which it would be theo- retically possible to realise from the amount of nitrogenous matter consumed. It has been shown by Professor Frankland 1 that the results of Fick and Wishcenus in reabty afford stronger evidence than they have contended for. Fick and Wislicenus were obliged to estimate the force-value of the nitrogenous matter, shown by the nitrogen in the urine to have been destroyed in the system, from the amount of force known to be producible by the oxidation of its elements, because the actual determina- tion for the compound itself had not been made. Professor Frankland, however, has since experimentally ascertained with the calorimeter the amount of energy or force evolved under the form of heat during the oxidation of a given quantity of nitrogenous matter as the oxidation occurs within the living system, in which position a portion, it must be borne in mind, of the carbon and hydrogen escapes being consumed, on account of being carried off by the nitrogen in the shape of urea. Frankland' s results give as the actual amount of energy pro- ducible from the nitrogenous matter consumed in the bodies of the experimentalists about half the quantity they had reckoned in their calculations. Thus, the results tell so much the more in Fick and Wislicenus' favour. Frankland con- siders, taking all points into consideration, that scarcely a fifth of the actual energy required for the accomplishment of the work performed in the ascent of the mountain could have been obtained from the amount of muscle (nitrogenous matter) that was consumed. Assuming, therefore, the fore- going conclusions to be entitled to credence, the doctrine which ascribes muscular action to oxidation of muscular tissue becomes utterly untenable. Dr. Parkes has conducted, in a most careful manner, a series of investigations on the influence of rest and exercise, under different diets, upon the effete products of the system, and, more particularly, to test the accuracy of the results arrived at by Fick and Wislicenus. He says, " Although these results [Fick and Wislicenus'] are supported by the. previous experi- ments of Dr. Speck, who has shown that, if the ingress of » " On the Origin of Muscular Power," 'Philos. Magazine,' vol. xxxii, 1866. 4 50 ALIMENTARY PRINCIPLES. nitrogen be restricted, bodily exercise causes no or a very slight increase in the elimination of nitrogen by the urine, it appeared desirable to carefully repeat the experiments, not only because the question is one of great importance, but be- cause objections might be, and, indeed, have been, reasonably made to the experiments of Professors Fick and Wislicenus, on the ground that no sufficient basis of comparison between periods of rest and exercise was given, that the periods were altogether too short, and that no attention was paid to the possible exit of nitrogen by the intestines." Dr. Parkes' experiments were conducted upon perfectly healthy soldiers, men who, when steady and trustworthy, as were the soldiers made use of, form, as Dr. Parkes observes, highly suitable subjects for experiments of the kind, their regularity in diet and occupation, and their habits of obedience, affording a special guarantee for the precision with which they will carry out the instructions given. There can, indeed, be little or no doubt, from the harmony observable all through, that the results furnish as exact and reliable information as can be hoped to be obtained. The total nitrogen contained in the urine was determined, as well as the urea ; and by this step more conclusive evidence is supplied than by the simple determination of urea, as had only been done in the experiments of Fick and. Wislicenus and others; obviously so, because it might be said that nitrogen escaped (as is really to some extent the case) in other forms than that of urea. The experiments consisted of two series, and extended, in each case, over several successive days. In the first series 1 a comparison is instituted of the products of excretion during rest and exercise under a non-nitrogenous diet. In the second 3 the same comparison is made under a fixed diet, con- taining an ordinary admixture of nitrogenous and non-nitro- genous food. In drawing conclusions regarding the destruction of muscle from the nitrogen eliminated, it is, of course, of the first im- portance that the whole of the voided nitrogen should be presented to our notice. Dr. Parkes is convinced, from his 1 ' Proceedings of the Royal Society,' Jan., 1867 vol. xv, No. 89. 5 Ibid., June, 1867, vol. xvi, No. 94. DR. PARKES EXPERIMENTS ON ELIMINATION OF NITROGEN. 51 experiments, that no nitrogen escapes either by the breath or perspiration, but that it is all to be found in the excreta from the kidneys and bowels. The nitrogen discharged by the bowels forms a comparatively small and varying proportion, and being derived from the undigested food and the unabsorbed digestive secretions, has no bearing in reference to the point before us. There remains, therefore, only the urinary nitrogen to consider as a measure of the tissue-metamorphosis occurring in the system. Thus prefaced, let us now see what light is thrown upon the matter under consideration by Dr. Parkes' experiments. For the sake of simplicity notice will only be taken of the total urinary nitrogen voided, as this gives in a more reliable manner than the urea the information that is wanted. The men forming the subjects of the first series of experi- ments are distinguished as S and T. T was a much smaller man than S (S weighing 150 and T 112 lbs.), and it will be observed that he, throughout, passed a less amount of urinary nitrogen. He did not consume quite so much food ; and as it was found that he discharged rather more nitrogen from the intestine, it may be assumed that he did not so fully digest and absorb what he ingested. For six days the men were kept upon an ordinary mixed diet, and pursued their customary occupation. The urine was col- lected and examined during four out of the six days, and the following is the mean amount of the total nitrogen passed per diem : — Mean urinary nitrogen. per diem. ( S 17'973 grammes. Mixed diet, with customary occupation . i T lg . 4og During the following two days the diet was restricted to non-nitrogenous food consisting of* arrowroot, sugar, and butter. The only nitrogen ingested— and this may be re- garded as too insignificant to require being taken into account —was in the tea the men were allowed to drink, it being thought desirable not to deprive them of this beverage. Throughout the two days they remained as much at rest as was practicable ; they were allowed to get up, but not to leave the room. 52 ALIMENTARY PRINCIPLES. Mean urinary nitrogen. per diem. ( S 9-176 grammes. Non-nitrogenous diet, with rest • { T 7" *, The men were now put back, for four days, upon a mixed diet, with customary occupation, just as at the beginning of the experiment. Mean urinary nitrogen.' per diem. ,,. j j- . -.i. *• f S 12-988 grammes. Mixed diet, with customary occupation < T 11-095 Next, they were restricted again for two days to the same non-nitrogenous food as before, but this time it was accom- panied with active walking exercise. During the first day the distance walked was 23|, and during the second 32f miles. The diet, it is stated, satisfied hunger, and there was no sinking or craving for other kinds of food. Mean urinary nitrogen. per diem. Non-nitrogenous diet, with active ex- 8 8-971 grammes, ercise . . . . (. T 8-034 To complete the experiment four more days were passed under observation with the ordinary mixed diet, accompanied by ordinary exercise. Rather more nitrogenous food was taken during these four days succeeding the two days' active exercise than during the four days succeeding the two days' rest, the men feeling more hungry after the ' ' work" period than after the period of " rest." The mean for T, it is mentioned, is for three days instead of four, one analysis having failed. Mean urinary nitrogen. per diem. Mixed diet, with customary occupation i j| j^l grammes. From this series of results we find that there was no material variation in the amount of urinary nitrogen discharged during the two days when a distance of 56£ miles was walked, as compared with the two days spent in as complete a state of rest as possible — on both occasions restriction to non-nitro- genous food being enjoined. Comparing both these periods, however, with those in which nitrogenous food was taken, we recognise a marked exemplification of the well-established DR. PARKES' EXPERIMENTS ON ELIMINATION OF NITROGEN. 53 fact that diet, on the other hand/ exerts a striking influence over the amount of nitrogen eliminated with the urine. During each of the non-nitrogenous diet periods the quantity of nitrogen eliminated was considerably less than during the others ; it is also noticeable that the influence of the non- nitrogenous food was extended into the subsequent ordinary diet-periods, less nitrogen being voided during these than at the commencement of the experiment, before any restriction from nitrogenous food had been imposed. This point, how- ever, will be futher alluded to hereafter. In the second series of experiments the amount of nitrogen eliminated was determined under the conditions of rest and exercise, combined with a mixed diet. One of the two men, S, was the same who had been made use of in the former experiment ; the other, B, was a fresh man, weighing 1401bs., and therefore nearer in size to S, who weighed 1501bs., than T, of the former experiment, who weighed 112 lbs. During the sixteen days over which the observations extended each man took precisely the same allowance of food in the twenty- four hours — the food consisting of weighed quantities of meat, bread, potatoes, and the other constituents of an ordinary mixed diet. For the first four days the men pursued their customary employment. The next two days were passed in rest. Then followed four days of ordinary employment ; after this, two days of active exercise ; and finally, four days again of ordinary employment. The amount of nitrogen eliminated by the kidneys during the several periods is shown in the following table : Urinary nitrogen. per diem. Ordinary employment (mean of four days) . \ B 18'502 -r. , c J ^ f S 19137 Kest (mean of two days) . ' ? B 19 - 471 Ordinary employment (mean of four days) . \ B 18-485 " Active exercise — walking on level ground, 24 f g 19646 miles the" first day, and 35 the second — < g 19959 " (mean of two days) . . • • v. f S Ordinary employment (mean of four days) . | g S 21.054 20.092 54 ALIMENTARY PRINCIPLES. In these results it will be seen that there is nothing to sanction the doctrine that the source of muscular power resides in the destruction of muscular tissue. In two persons subsist- ing on an identical and unvarying daily diet, and subjected to varying conditions of muscular exertion, we find nearly the same quantity of nitrogen eliminated during two days' hard walk- ing as during two days of- rest. It is curious, and also, it must be owned, does not appear explicable, that during the periods of both rest and active exercise the daily amount of nitrogen eliminated was in excess of that eliminated during the first two periods of ordinary employment, the figures at the same time for the associated periods respectively agreeing very closely with each other. In the third period of ordinary employment — that is, after the two days of walking exercise — the nitrogen voided was greater in quantity than at any other time. Such excess, however, did not amount to any- thing particularly marked. Comparing in detail the nitrogen eliminated during tie corresponding portions of the two day-periods — those of rest ' and active exercise — Dr. Parkes observes, with respect to the results furnished : " On the first day of exercise, the nitrogen in each man fell below the corresponding day of rest by l - 626 and 1/131 grammes. In the next twelve hours, which were almost entirely occupied in exercise [this period extending from 8 a.m. to 8 p.m. J, the diminution was still greater, being 2'498and 1*225 grammes, which would be equivalent to 5 and 2\ grammes for twenty-four hours. In the last twelve hours [8 p.m. to 8 a.m. J of rest after work, the elimination increased greatly, so that 5"142 and 3"331 grammes more were excreted than in the corresponding rest period." Seeking to reconcile his results in relation to' mus- cular action, Dr. Parkes observes : " It appears to me that we can only express the facts by saying that a muscle during action appropriates more nitrogen than it gives off, and during rest gives off more than it appropriates." But must we, I would suggest, look only to the muscles for the source of the variation in the amount of nitrogen dis- charged in these experiments ? The results, in the firsj place, conclusively showed that the nitrogen eliminated forms no . measure of muscular work performed, and hence it may be DR. FARKEs' EXPERIMENTS ON ELIMINATION OP NITROGEN. 55 inferred as a corollary that muscular work is not a result of muscular destruction. But, taking the variation in the voided nitrogen that was observable, independently of that occasioned by diet, why should we seek its source exclusively in the muscles ? On looking at the several daily amounts discharged, I re- mark the existence of instances in which considerable variation occurs within the periods themselves. Thus, during the first day of the first period, when the men were engaged in ordi- nary employment, B discharged 20-417 grammes of nitrogen, and during the third day only 17-090, a difference approach- ing to 3£ grammes. Again, during the last period, which was also spent in ordinary employment (it will be remembered that the daily diet was the same throughout the experiment), the urinary nitrogen voided by both men stood as follows : S B First day . . 2125 grammes . . 2025 grammes. Second day. . 19942 „ . 19273 „ Third day . . 23488 „ . . 19-248 ,', Fourth day . . 19536 „ . . 21-597 On the third day, it thus appears, S discharged nearly four grammes of nitrogen in excess of that on the fourth, and about 3 \ in excess of that on the second. No corresponding fluctua- tion, it will be remarked, was observable in the case of B. Here, then, are marked variations in the elimination of nitro- gen without a variation of muscular action. In a more recently performed experiment 1 Dr. Parkes' results show, with a fixed daily ingress of nitrogen, a variation in the daily exit amounting in the extreme to seven and a half grammes. Now, we know that the nitrogen of the urine is derivable from the metamorphosis of the nitrogenous ingesta within the system. It is true the food taken was every day the same throughout the experiment that has been forming the subject of consideration, but it does not follow that the rate of metamorphosis was every day similarly identical. Doubt- less, like other processes of life, it is influenced by various internal conditions. We know also, as the result of obser- vation in the case of starvation, that, notwithstanding an 1 'Proc. Roy. Soc.,' March, 1871. 56 ALIMENTABY PRINCIPLES. absence of ingoing nitrogen, an elimination of this element still continues, and that the nitrogen eliminated is drawn from the nitrogenous principles of the body, belonging alike to the solids and fluids. There is a general waste or loss occurring, and the only difference noticeable is that the loss goes on with different degrees of rapidity in the different parts of the sys- tem. In the muscles it certainly occurs somewhat more rapidly than elsewhere, but this is all. "With these considerations before us it appears to me that we are taking an unjustifiably narrow view in looking only to the muscles to account for the variation in question in the voided nitrogen. Exercise cannot fail to influence the processes going on in the system generally, as well as in the muscles, and, in accounting for the results observed, instead of limiting ourselves, with Dr. Parkes, to the assertion that " we can only express the fact by saying that a muscle during action appropriates more nitrogen than it gives off, and during rest gives off more than it appropriates," I think what we ought rather to say is, that during exercise the system appropriates more nitrogen than it gives off, and during rest gives off more than it appropriates. Voit, however, . disputes the reality of exercise producing any influence over the elimination of nitrogen, and has taken exception to some of Dr. Parkes J experiments, on the ground, more particularly, that the daily ingress of nitrogen could not be kept sufficiently stable. This elicited from Dr. Parkes his further series, the results of which are recorded in the ' Pro- ceedings of the Royal Society ' for March, 1871. In these it appeared that there was no change induced, either at the time or afterwards, by a moderate amount of additional exercise under a mixed regulated diet ; but, under a non-nitrogenous diet, the increase in the nitrogen on the following day to the performance of a hard day's march was exceedingly striking. The non-nitrogenous diet was continued through five succes- sive days. " During the first three it was associated with the ordinary work of a soldier ; on the fourth, with a march of thirty-two miles, performed with a load of 43| lbs. ; and on the fifth with rest, As the ordinary result of abstinence from nitrogenous food, the eliminated urinary nitrogen underwent a steady decrease during the first four days ; on the fifth, mr. weston's walking feat and eliminated nitrogen. 57 however, it stowed a marked ascent, the amount being then in considerable excess of that discharged on the first. In the ' New York Medical Journal ' for October, 1870, Dr. Austin Flint, jun., records the result of the examination of the urine secreted during the performance of, perhaps, an unprecedented amount of muscular work within the space of time occupied. A Mr. "Weston, set. 32, of medium height, and weighing ordinarily 122 lbs. without his clothes, celebrated as a pedestrian of the United States, undertook to perform the astonishing feat of walking one hundred miles in twenty-two consecutive hours. The feat, it appears, was accomplished within the time — namely, in twenty-one hours and thirty-nine minutes. The food consumed during the period was taken in small quantities at short intervals, and consisted of between one and two bottles of beef essence, two bottles of oatmeal gruel, and sixteen to twenty raw eggs, with water. Mr. Weston drank, it is said, a little lemonade and took water very frequently, but only in quantity sufficient to rinse his mouth. While walking the last ten miles he took, it is further stated, two or three mouthfuls of champagne, amounting to about three fluid-ounces, and about two and a half fluid-ounces of brandy in ten-drop doses. The head and face were sponged freely at short intervals, and the food and drink were taken mainly on the walk, which was conducted within- a covered enclosure. The urine passed during and at the completion of the walk measured 73£ fluid ounces, and presented the specific gravity of 1011. According to Dr. Flint's analysis it contained 424| grains of urea. Now, 500 grains form about the average daily quantity of urea discharged under an ordinary mixed diet ; and as the diet during the performance of the pedestrian feat was rich, as the account shows it to have been, in nitro- genous matter, the quantity of urea, apart from any other consideration, was even less than might have been expected. And yet, on the strength of a comparison with another ex- amination of the urine conducted three months later, when only 191 grains of urea are stated to have been discharged in the absence of exposure to muscular exertion, Dr. Flint argues that muscular exercise notably increases the elimination of urea. To take a solitary result of so exceptional a kind as 58 • ALIMENTARY PRINCIPLES. the discharge of only 191 grains of urea in the twenty-four hours, and use it as a ground of comparison for reasoning upon, as Dr. Mint has done, is surely to violate all rules of sound induction, and it is to be hoped that we shall not find the observation quoted by writers as bearing out what Dr. Flint has contended for. During November, 1870, Mr. Weston undertook another pedestrian feat, and this time a very elaborate examination was made of the ingesta and egesta, and of various conditions of the body, by Dr. Flint and a staff of associates. The results are recorded in detail in the 'New York Medical Journal' for June, 1871. The feat proposed was to walk 400 miles in five consecutive days, and upon one of the days 112 miles were to be walked in twenty-four consecutive hours. Mr. Weston commenced the undertaking on the 21st of November. The examination of the ingesta, egesta, &c, had been conducted for five days before ; it was also carried on during the five days of the walk, and continued for five days afterwards. Thus, the results for three periods — before, during, and after the walk — were obtained. The subjoined tabular representation will give a summary view of the lead- ing points noted. The walk was undertaken over a measured track marked out in the form of a parallelogram, within a large covered space — namely, the Empire Skating Rink in New Tork. It appears that Mr. Weston failed this time to accomplish the feat he had attempted; the distance walked during the five days amounting to 31 1\ miles, and the greatest distance on any one day to 92 miles. Notwithstanding the figures to be presented Dr. Flint still holds to his former opinion, and looks upon the results as showing, to use his own words, that " excessive and prolonged muscular exertion increases enormously the excre- tion of nitrogen, and that the excess of nitrogen discharged is due to an increased dis-assimilation of the muscular substance." ME. WESTON'S WALKING FEAT AND ELIMINATED NITROGEN. 59 Dr. Flint's observations on the effects of the five-day pedest feat performed by Mr. Weston. ■nan Weight of body (nude) Before the walk. lb. First day . 1205 Second Third Fourth Fifth During the walk. First day . 1165 Second Third Fourth Fifth After the walk. First day . 118- Second . 12025 . Third . 120 25 . Fourth . 1235 . Fifth . 12075 . 121-25 120- 118-5 119-2 11625 . 115- . 114- . 115-75 • Tem- perature. raise. Miles walked. Nitrogen in ingesta. Nitrogen in egesta. Fahr. Grains. Grains. 99-7° . 75 . 15 . 361-22 . 323-26 98-4 , , 73 . 5 . 288-35 . 301-18 98-0 . 71 . 5 . 272-27 , . 330-36 991 . 78 . 15 . 33501 , , 300-57 99-5 . 93 . 1 . 440-43 , . 32006 Excess or deficiency in nitrogen egested. Grains, — 3796 12-83 58 09 34-44 120-37 + + 95-3 94-8 96-6 96-6. 979 98-6 98-4 993 98-8 975 98 . 80 . 151-55 . 35710 93 . 48 . 26592 . 37064 109 . 92 . 228-61 . 397-58 68 . 57 . 144-70 . 348-53 80 . 405. 38304 . 33277 . 76 73 70 78 76 2 2 2 2 385-65 . 295-70 49910 . 358-81 39483 . 409-87 641-71 . 382-89 3 . 283-35 . 418-49 + 205-55 + 104-72 + 168-97 + 203-83 — 50-27 — 89-95 — 14029 + 15-04 — 258-82 + 135-14 Let us accept Dr. Flint's estimates of the ingoing and outgoing nitrogen. It is true, during the first four days of the walking period the exit of nitrogen was in considerable excess of the entrance ; but why should this be referred specially and exclusively to muscular disintegration ? There was during these few days a progressive decline in the weight of the body, the loss reaching a little over 5 lbs. From the account given, considerably less solid food was taken then than before and after. There existed a state of marked dis- turbance of the bodily functions, as shown by the depression of temperature and elevation of pulse ; but little sleep was obtained; and on the third day, when an attempt was made to walk the 112 miles in twenty-four consecutive hours, drowsiness, it is stated, prevailed to such an extent that it was found impossible to make the necessary time to accom-. plish what had been intended. On the fourth day Mr. Weston actually broke down for a time altogether, becoming dizzy, staggering, and at last failing to be able to see sufficiently to turn the corners of the track. 60 ALIMENTARY PRINCIPLES. Now, apart from the fact that a marked deviation from the physiological state existed when the results, upon which the conclusions are based, were yielded, is there anything in the results to show that in reality we have more to deal with than simply a consumption of nitrogenous material within the system beyond the supply for the time from without" ? Taking the figures throughout, there is not much more to be seen than a difference occasioned by a falling off in the amount of nitrogen ingested during the first four days of the walk ; and it is well known that when the ingesta do not furnish what is wanted for meeting the expenditure going on (as during inanition), the resources of the body are drawn upon, and the nitrogenous matter existing in the various parts — both solids and fluids — wastes or yields itself up as well as the rest. On the fifth day, after a prolonged sleep, which appears to have restored the flagging powers, the previous relation was reversed. The food ingested afforded more than enough to meet the requirements. There was a gain of If lb. in body-weight, and, according to the figures, the nitrogen discharged fell short by 50*27 grains of that which entered, notwithstanding a walk of forty miles and a half was performed. The distance walked during the five days amounted to 317-J miles, and the excess of nitrogen eliminated during the time, over that ingested, appears to have been 633 grains. Presuming, for sake of argument, this to have represented the nitrogen of muscle disintegrated in the accomplishment of the work performed, we have before us the data for ascer- taining how far the force producible in this way would correspond with the expenditure that must have occurred. According to Mulder's analysis, albuminous matter con- tains 15 - 5 per cent, of nitrogen. Reckoning from this proportion, 633 grains of nitrogen will correspond with 4083 grains of dry albumen, and the composition of the nitro- genous matter of muscle is closely analogous. Now, the force producible from the oxidation of albuminous matter has been experimentally ascertained by Frankland; and, as it occurs within the body, the oxidation of 4083 grains of dry albumen would give rise to the evolution of an amount of power equal to lifting 1540 tons one foot high. Here we have one side of the question — the amount of RESUME OF PREVIOUS CONSIDERATIONS. 61 work obtainable from the nitrogenous matter presumed to have undergone disintegration as muscular tissue ; and so far the information in our possession may be regarded as suffi- ciently authentic to enable us to frame a reliable conclusion. As regards the work accomplished, we may assume, with Professor Haughton, that the force expended in walking or progressing on level ground is equal to that required to lift one twentieth of the weight of the body through the dis- tance traversed. The distance walked amounted to 31 1\ miles, and if we take the weight of the body and clothing at, say, 120 lbs., this "will give the performance of an amount of work equal to lifting 4490 tons one foot high, or about two thirds more work than the oxidation of the nitrogenous matter representing the 633 grains of nitrogen could accom- plish. And, in this calculation, only the external work has been taken into consideration. There is, in reality, also a considerable amount of internal work constantly being performed — viz. that employed in keeping up the circu- lation, inrespiration, and in various other essential actions of life. I have entered thus minutely into the question of the elimination of nitrogen in relation to muscular work because it bears in so forcible and direct a manner upon the question immediately before us — viz. the uses to which the nitrogenous alimentary principles are applied in the system. Briefly re- presented, the position of the matter may be said to be this : Many years ago it was asserted by Liebig that muscular action involved the destruction of muscular tissue. The plausibility of the doctrine, and the readiness with which the views of its author were then received, must be considered as having led to its being at once generally accepted as though it formed a scientific truth, although, in reality, only consti- tuting a speculative proposition, unsupported by anything of the nature of proof. It was further argued that, if muscular action involved the destruction of muscular tissue, the excretion of the nitrogenous product of destruction — urea — ought to be in proportion to the amount of muscular work performed. This seemed to follow as a necessary sequence, and the one being accepted, the other was taken for granted also. Thus, not- withstanding the absence of anything in the shape of proof, 62 ALIMENTARY PRINCIPLES. we find physiologists reasoning and writing as though the doctrine had been actually proven. If the theory of Liebig were true, we should have to look upon nitrogenous alimentary matter as forming, through the medium of muscular tissue, the source, and the only source, of muscular power. The renewal of muscular tissue for sub- sequent oxidation in its turn, and evolution of muscular force, would thus constitute one of the functions of nitrogenous alimentary matter ; and on its supply would, accordingly, depend our capacity for the performance of muscular work. It is only lately that the doctrine has been submitted to the test of experiment, and with what result the foregoing account of the researches of various observers has shown. Even Liebig 1 was brought to assert that muscular action is not attended by the production of urea. He admitted that the question as to the source of muscular power had been compli- cated by an inference which had proved erroneous, and for which he acknowledged himself as responsible — the inference, namely, that muscular work is represented by the metamor- phosis of muscular tissue, and the formation of urea as a final product. "While admitting this much, however, Liebig still looked to changes in the nitrogenous constituents of muscle as the source of muscular power. He assumed the presence in muscle of nitrogenous substances in a much higher state of tension than syntonine and albumen, and to these he referred the performance of muscular work, taking shelter under the proposition that it is due to the liberation of the tension thus presumed to have been accumulated in them during their formation. The application of food to the genesis of muscular power will form the subject of further consideration hereafter, when we reach the head of non-nitrogenous matter. Suffice it here to reiterate that muscular action is not to be considered as the result of muscle-destruction, as was formerly supposed, and hence that nitrogenous matter is not applied through muscle — in the manner hitherto maintained — to the develop- ment of muscular force. Thus much, from the evidence before us, may be said, but, at the same time, common expe- 1 " Proceedings of the Royal Bavarian Academy of Science," 1869. ' Phar- maceutical Journal,' 1870. NITROGENOUS FOOD AND HEAT-PRODUCTION. 63 rience seems to show that a plentiful supply of nitrogenous matter in the food tends to increase the capacity for the performance of muscular -work. If, however, it does so in any other way -than by supplying material for nutrition and the secretions, and so contributing to the production of a fully-nourished and vigorous state of the system, we have no data before us to indicate how. Let me next draw attention to the application of nitro- genous matter to force-production by the direct utilisation of the carbon and hydrogen it contains. Liebig's doctrine, which, until recently, has formed the accepted one oh this point, was that nitrogenous food, to be turned to account for force-production, must pass through the condition of living tissue. This brings us back to the discussion that has pre- ceded, with the addition that our nitrogenous food must perform work as tissue to enable it to be susceptible of appli- cation to force, — or — say heat-production. Thus, in his work on f Animal Chemistry,' at page 60, Liebig says, " the flesh and blood consumed as food yield their carbon for the sup- port of the respiratory process, whilst the nitrogen appears as uric acid, ammonia, or urea. But, previously to these final changes, the dead flesh and blood become converted into living flesh and blood, and it is, strictly speaking, the carbon of the compounds formed in the metamorphosis of living tissues that serves for the production of animal heat." Again, at page 77, we find — " Man when confined to animal food respires like the carnivora at the expense of the matter produced by the metamorphosis of organized tissues ; and just as the lion, tiger, and hyaena, in the cages of a menagerie, are compelled to accelerate the waste of their organized tissues by incessant motion, in order to furnish the matter necessary for respiration, so the savage, for the very same object, is forced to make the most laborious exertions and go through a vast amount of muscular exercise. He is compelled to consume force merely in order to supply matter for respi- - ration." Once more, in speaking of the derivation of urea from the metamorphosis of nitrogenous matter, he says, at page 144, " There can be no greater contradiction with regard to the nutritive process than to suppose that the nitrogen of 64 ALIMENTARY PRINCIPLES. the food can pass into the urine as urea, without having pre- viously become part of an organized tissue." Liebig's idea, then, upon this point is very precise. He considers that nitrogenous matter may contribute towards heat-production, but that it must- first pass into the condition of tissue before it can do so, and that it is in the wear and tear of tissue that occurs the splitting up of the compound, so as to lead to the production of urea for secretion on the one hand, and the liberation of- carbon and hydrogen for oxidation on the other. The facts which have been already adduced suffice to refute this doctrine. Indeed, it may be considered as now abun- dantly proved that food does not require to become organized tissue before it can be rendered available for force-production. But Liebig, himself, in language not less precise than that which he at first -employed, has recently x given utterance to words which directly contradict his original view, inasmuch as he now asserts that muscular work and the production of urea bear no immediate relation to each other, and that among the products formed as the result of muscular action, urea certainly does not even constitute one. If the elimination of urea, as has been shown, is not related, as was formely supposed, to muscular action, it is, on the other hand, in a very direct manner influenced by the food ingested. As far back as 1854, Messrs. Lawes and Gilbert, in opposition to the views then prevailing, showed by the results obtained in their observations on the feeding of cattle, that the nitrogen in the urine is related to that in the food, and not to the muscular work ; and, since then, the concurrent testimony of numerous observers, as has been already pointed out, may be held as completely establishing this position. Lehmann's well-known experiments upon himself strikingly illustrate the extent to which this influence is manifested. The results he obtained were as follows : While living on a purely animal diet, namely, almost ex- clusively on eggs, Lehmann passed 53 - 2 grammes (820 grains) of urea in the twenty-four hours as the mean of twelve obser- vations. 1 ' Proceedings of the Koyal Bavarian Academy of Sciences,' 1869. METAMORPHOSIS OP NITROGENOUS MATTER. 65 Upon a mixed diet the urea amounted to 32 - 5 grammes (501 grains), as the mean of fifteen observations. Upon a vegetable diet the urea given as the mean of twelve observations was 22 "5 grammes (347 grains). And, lastly, upon a purely non-nitrogenous diet (fat, sugar of milk, and starch), he voided, as the mean of three observa- tions, only 15*4 grammes (237 grains) of urea. It is thus seen that upon an animal diet, which is the richest in nitrogenous matter, the voided urea more than doubled that eliminated upon a vegetable diet, while the amount of urea voided upon a mixture of the two kinds of food held an intermediate position. When no nitrogenous matter was ingested the urea was at its minimum. What was then passed would be derived from the metamorphosis of the nitrogenous matter belonging to the blood and the other constituents of the system. Some experiments of Schmidt show, also, in accordance with the results obtained by Lehman% that the amount of urea passed is related to the quantity of food ingested, the nature of it remaining the same. Schmidt found that a eat excreted the following relative amounts of urea to body- weight under the consumption of different amounts of meat : Daily amount of Daily amount of urea excreted meat eaten. per kilogramme body-weight. 44-188 grammes . . • 2-958 grammes. 46154 „ ... 3050 „ 75-938 „ ... 5152 108755 „ ... 7663 „ From these results it may be computed that a cat^ living on a flesh diet, discharges by the kidneys on an average &8 parts of urea for every hundred parts of meat consumed. The great bulk of the nitrogen belonging to the food ingested thus passes out of the system in the form of urea. If all escaped in this way the quantity of urea discharged would amount to (say) 7-88 per cent, of the weight of the meat; the nitrogen contained in 100 parts of flesh corre- sponding with that contained in 7'88 parts of urea. There were, then, 6'8 parts of urea produced instead of the 7"88 parts, which may be spoken of as representing the actual equivalent, as far as contained nitrogen is concerned, of 100 parts of flesh. 5 66 . ALIMENTARY PRINCIPLES. Lehmann, from his observations on himself, asserts that as much as- five sixths of the nitrogen of the ingested food were found in his urine under the form of urea. For example, while living upon a purely animal diet, consisting of thirty- two eggs. daily, he ingested about 30*16 grammes of nitrogen, and, in the urea voided, discharged about 25 grammes of nitrogen. The discharge of urea being thus proportioned to the amount of the nitrogenous matter ingested, it follows that nitrogenous matter must undergo metamorphosis of such a nature within the system as to lead to the production of urea. Further, it may be said that this metamorphosis must take place rapidly as it is found that the effect upon the excretion of urea quickly follows an alteration in the food ingested. Lehmann, for example, again drawing from his observations on himself, noticed, in the morning after he had lived exclusively on animal food, that his urine was so rich in urea as to throw down a copious precipitate of the nitrate, on the addition of nitric acid. In Dr. Parkes' observations, also, upon the two soldiers S and T before referred to, the alterations in the food ingested speedily influenced the amount of urea escaping. These men were, first of all, kept for four days upon a regulated mixed diet ; next for two days upon a non-nitrogenous diet; then, again, for four days upon a mixed diet; afterwards for two days on a non-nitrogenous diet ; and, lastly, for four days on a mixed diet. S, during the first four days, on the mixed diet, passed 35. grammes of urea as the daily mean. During the first day of the non-nitrogenous diet he passed 20, and during the second, 13*52 grammes. Resuming the mixed diet, he passed, on the first day, 20*67 grammes of urea; on the second, 25*68 grammes; on the third, 26*29; and on the fourth, 29 "6 7. Changing, again, to the non- nitrogenous diet, he passed on the first day 19*12, and on the second, 15*00 grammes of urea. On the next four days, the diet being a mixed one, he passed, during the first day, 20*8 ; the second, 26*36; the third, 28*32; and the fourth, 30*10 grammes of urea. With T (a much smaller man than S) the mean, for the first four days of mixed food, was 25*92 grammes of voided urea. During the next two days, upon , non-nitrOT genous food, he passed, on the first day, 17*3; and on the METAMOEPHOSIS OF NITEOGENOUS MATTER. 67 second, 12*65 grammes. On the following four days, upon a diet of mixed food, he voided 14*40 grammes the first day ; 23-00 the second; 25*20 the third; and 22-99 the fourth. During the next two days, resuming the non-nitrogenous diet, he voided 16*00 the first day, and 13*20 grammes the second. With the return to a mixed diet during the following four days the urea stood at 23*00 on the first ; 24*36 on the second ; 24*57 on the third; and 21*36 grammes on the fourth. Although conducted for settling another point, it will be seen that these observations very clearly and consistently throughout show that the production and elimination of urea are speedily affected by the ingestion of nitrogenous matter. With the view of obtaining more precise information re- garding the time required for the metamorphosis of nitrogenous matter to occur and lead to an increased elimination of urea, Mr. Mahomed, whilst formerly assisting me in my laboratory, carried out, with laudable zeal and self-denial, two series of experiments upon himself, the particulars of which I will in- troduce here. It may be mentioned that he was 22 years of age, 6 feet in height, and list. 111b. in weight. The method of procedure had recourse to was to diminish the elimination of urea by limiting in one experiment, and withholding in the other, the introduction of nitrogenous matter, and then note within what space of time the ingestion of nitrogenous matter showed its effects upon the urine. The first experiment was commenced on April 16th, 1871. Mr. Mahomed had been previously living upon an ordinary mixed diet, and took his dinner of mixed food, as usual, at 1.30 p.m. From this time he restricted himself to rice, arrowroot, butter, sugar, and tea". Eice was allowed that he might not suffer too much privation, and as being one of the least nitrogenous of the natural food products. The diet was continued throughout the 17th, and at 8 a.m. on the 18th, four eggs— purposely to supply nitrogenous matter— were eaten. This was the only deviation from the' diet of the pre- ceding day, so that an opportunity was given for the urea to be again at a low point on the following morning, when a meal consisting mainly of meat was taken. Subjoined is a representation of the results obtained, arranged in a tabular form : 68 ALIMENTARY PRINCIPLES. CO a. co ■«. o § «£» | co' s> s. <» ■I «» S 'S ■&» &> s s o 50 F k* s -w s? ^- >*5 CO -Ki Si o §" fci a> 3 | 3° I OS .P „ . * OS ■s I r^ - . O J* « T3 IS <" - P .3 O * flO." 3 Q ^ 1 ! rO -Q tf ° • 2 S 1 aS- 5 a a n ««*H o « -a o >\> to - fe u m a <" CO CO *^ r^ O o ego n3 "S bs r*-*~~\ t-. ^ «4S * at o O /-**— \ r4 CD flj §T3 OT3 o * Bl /~*— ■ 3 s * a r ^_ 9 h i' 3 'Ha ft. o o 5* 03 Oh CO GO CO Oh ca- co co Hibos 00 00 oo co oa 00 i-H cb 6 O P wl ' ' r—>~~ s f 1 f "t I Si a »~ COCONO) « U3COHCO 05 (35 CO >0 CN CO tp -Jt) •Jl ■^ so ■—« *b cb ■—» f- CO OS (N « ■"* oo CN Tftb A i— 1 i— 1 i— i i-H i-H i-H r-l . ° o U >o +j u 3 IS-O •O O «5 IS O .*?.*? _ t OJIO CM «0 CN *& co 65 i^H CO Tf r-l hosAho O ■* b-t-l> %l 1 HHHIN i-< (M .2 3 .2 . 2 ja r/j . t< a c _ ° g »0 «s - > O ^ tt sea) §5? C T3 - c p-; CU 03 "3 'd to 60 c Oh £ § o <2 52 | c 3 00 m p; „ . .p. cj S II M 3 CU -e is a t. o*™." a s M c g c S a. o u -a O o 1*4 s p*> C3 .g •3 O OJ O c8 g 5 § g-s'S <» ° 02 , . ^ s a - . Ma &> « ft s S _ .5 * s s = £ SE„ SB s s 30000 *: ea ci. " " 03 fij 03 CO CO CO CO rt CO CO 00 i— t~ Oi 00 CN CO OS co ph p-i t^ oi pH 00 00 (N CO OS "3.3 5 £ »-* « f ^ r A • JV 2 O a B £ ° * "pS c * =- B ■* >« »~ OJ to-jowa 00 CN CO ■* US t-" CO CO O >"^ ^P "3 ■71 ■* in cj -p f t- 10 »ro ooimNn CO W SO « *» IfUi I pp t-fr. 00 O CO CO ph CO os q p-t co os T|<«5HN _ ao 00 cp 63 ph CN CN CN CO CO «5 CO Tf t(i CO *o 00 ^t* CO ^ ^C d p-l PH p-l pH pH h-"m »-r 0 >o ■ 3 »- CN smso >o t~ *^. W (N tN 11 O eo co CO CN 00 W3 tn. 10 US CO CO CO CO rH 5 " p CO i a eo 6 © CN *- ■* •* A ■* lO «5 OS T)l CO "^f CO CO 00 ^J* *-* •— 1 f-* 1— 1 pH pH P-i PH PH 1— 1 -w *5 p3 -a a* . 60 a .a° S r:8 s 1 i *.i 09 . a ° S .s =0 c 0. a SSo.g« •go- 3 - . - * E p,* «• a. *' s a a. «" * § °* s °- =» 3 S 2 00 °* o< oh'?9?h fe" pH Tj< GO pH "HINOOOH OOOO °oo°o ^ C O O C5 O o s a a . g s . 03 & s e a - Co c q Soi "P. c q p> q q coo a ao* ph -^i 00' m 00' CN -4 CO CN 00' CM "* 00' CN CO p-T CN «5 CO U •-< PH pH pH pH Is V_— v^— ' I y- -v- V ' n ja ja ja ja *a *a «a *3 «5 CO t» 00 p»> p>. k, p^ 63 es 03 03 8 § » US METAMORPHOSIS OF NITROGENOUS FOOD. 71 It will be seen that the above results harmonise with those obtained in the first experiment, and show that the ingestion of nitrogenous matter is followed by a speedy metamorphosis and production of urea. Under the two days' restriction to non-nitrogenous food the urea fell from a range of 21 to 25 grains per hour to 8'87 grains per hour. Nitrogenous food was now taken, and the form of egg and milk beaten together was selected, that, on account of its fluidity, absorption might be rapid. Half an hour later an ordinary breakfast with cold meat was eaten. During the three hours succeeding the first ingestion of nitrogenous matter the urea secreted amounted to 12 "43 grains per hour against 8 - 87 grains per hour, the mean amount given for the eight hours previously. During the next three hours it stood at 14' 13 grains per hour, and afterwards showed a steady increase throughout the day. It is true between 8 - 87 and 12"43 grains per hour there is not the difference that was noticeable on the morning of April 19th, in the first experiment ; but I think it may be fairly assumed that evidence is afforded of the production and elimination of urea within the three hours from the nitrogenous matter ingested at the commencement of the time. Through- out the day the urea was less in quantity than during the corresponding period in the first experiment, which may be due to the more complete restriction having led to a greater exhaustion of nitrogenous matter, and thereby, owing to the greater demand for the requirements of the system, a less surplus having existed for metamorphosis into urea aud the complemental hydro-carbonaceous portion. For supplying solid food during the restriction, the arrow- root was made into biscuits with butter, sugar, and water. Mr. Mahomed remarked, on rising on the morning of the 7th, that he felt depressed, and experienced a general want of tone. Before the meal in the middle of the day he felt very hungry and thirsty, but these sensations disappeared after partaking of a basin of arrowroot, two of his arrowroot biscuits, and a cup of tea. He walked afterwards between five and six miles without any distress. Between the 5th and the 8th he lost one pound in weight. The urine, it may be observed, as in the first experiment, underwent a marked diminution in quantity with the return to nitrogenous food. 72 ALIMENTARY PRINCIPLES. It is a noteworthy point that between noon and midnight of the second day's restriction the urine presented an alkaline reaction. The same feeling of weakness was experienced upon rising on the morning of the 8th as on that of the preced- ing day. Although it has been clearly ascertained that a more or less large proportion of the nitrogenous matter ingested under- goes metamorphosis attended with the production of urea, yet, as to the precise seat of metamorphosis, our information at present warrants, it must be said, little more than a surmise being formed. According to the old doctrine of muscular action, the chief portion was thought to be produced in the muscles ; but even Liebig now argues (abstractedly from the doctrine in question) that the absence of urea as a constituent of muscular tissue may be taken as affording presumptive evidence of its production occurring elsewhere. While absent from flesh, or, if present, only so to a barely appreciable ex- tent, it is, according to Meissner and others, to be detected in mammals in considerable quantity in the substance of the liver ; and, in birds, where uric acid holds the position of urea, this has been similarly found in the liver. Other con- siderations have been also advanced in support of the liver forming the seat of metamorphosis of nitrogenous matter attended with the production of urea, but the point is one which requires to be further investigated. Having brought the subject before us to this point, the next question for consideration is, what purpose is subserved by the metamorphosis of nitrogenous matter that has been shown to occur. It has been hitherto the custom to look upon the nitro- genous matter which undergoes this transformation as holding the position of superfluous alimentary material — "luxus con- sumption," as it has been styled. Thus, Lehmann writes : — " In the present state of our knowledge we may say that urea is formed in the blood, and that it is produced from materials which have become effete — the detritus of the tissues — as well as from unserviceable and superfluous nitrogenous substances in the blood." As albumen fails under natural circumstances to pass off as such from the system, it was thought that, METAMORPHOSIS OP NITROQENOTJS POOD. 73 when introduced in excess of the requirements of nutrition, it underwent a retrograde metamorphosis of such a nature as would admit of the escape of its elements. It is perfectly true that the process which occurs does constitute a retrograde metamorphosis ; but the question presents itself whether it is simply designed as a means of exit of surplus matter, or whether it is not preparatory to some useful purpose being fulfilled by a part of the nitrogenous compound. The fundamental fact to be dealt with is, that nitrogenous matter undergoes a metamorphosis in the system attended with the production of urea. Now, let us look at the chemical constitution of these bodies, and see what this transformation implies. The per-centage composition and chemical formulae are at our disposal to appeal to, but the former is the most suitable for our purpose ; for although the atomic constitution of urea has been agreed upon, yet, as regards the albuminous molecule, it cannot be considered that we know with any degree of certainty the exact number of atoms of the different elements belonging to it, much less the precise mode in which these atoms are grouped. The formula, therefore, that can be given for it is only hypothetical. The per-centage composition, however, has been ascertained with sufficient precision to serve as a trustworthy basis for the calculation about to be made, and the deduction to be drawn from it. Let us take, for our calculation, Mulder's analysis albumen, which is as follows : Carbon • 53 ' 5 of Hydrogen Nitrogen Oxygen Sulphur Phosphorus 7-0 15-5 220 1-6 0-4 1000 On looking at these figures, it will be seen that the nitrogen belonging to albumen amounts to 15'5 parts in 100. Now, let us suppose, as it is not very far from being actually the case, that the whole of the nitrogen of the in-going albumen escapes from the system under the form of urea. In thus escaping as urea the nitrogen carries with it a certain portion of the other constituent elements of albumen, 74 ALIMENTARY PRINCIPLES. and by ascertaining of what this portion consists, we shall see .what remains behind to be disposed of in another way. To obtain the information required, we must first be in possession of a knowledge of the relative proportion in which the elements exist in urea. This is supplied by its per-centage composition, which stands as follows : Carbon ...... 20000 Hydrogen ..... 6 - 666 Nitrogen ...... 46'667 Oxygen ...... 26-667 100000 Now, to give to 15" 5 parts of nitrogen (the quantity of nitrogen existing in one hundred parts of albumen) the due proportion of the other elements required to form urea, we shall have to supply 6"64 parts of carbon, 2*21 of hydrogen, and 8"85 of oxygen. In other words, the 15*5 parts of nitro- gen contained in 100 of albumen, in escaping as urea, will carry with it 6*64 parts of carbon, 2*21 of hydrogen, and 8 "85 of oxygen — leaving a residuary portion consisting of 46"86 parts of carbon, 4*79 of hydrogen, and 13"15 of oxygen, besides the sulphur and phosphorus for utilisation and exit in another way. Thus, 33*20 per cent, (or, as nearly as possible, one third) of the albumen will be turned into urea, and 66*80 per cent, (or, as nearly as possible, two thirds) of complemental matter will be left. Urea must be regarded as constituting the unutilisable portion of the albuminous principle. Whether it is formed as a primary product of the splitting up of albumen— that is, whether the elements at once group themselves from the albuminous compound into the combination .representing it — or whether it . forms the final product of a series of changes, cannot be stated. Prom comparing the egesta with the ingesta we know that it is produced. But what constitute the actual steps of metamorphosis within the system remains for physio- logical chemistry to disclose. It may be remarked incidentally that, taking urea as an effete product of the metamorphosis of albuminous matter within the system, and looking at its composition under a METAMORPHOSIS OP NITROGENOUS POOD. 75 certain point of view, we discern a relation to other products of the decomposition of nitrogenous matter that does not suggest itself on looking at its composition as ordinarily repre- sented. Carbonic acid, ammonia, and water are the final products into which all nitrogenous matter of an organic nature is constantly tending to resolve itself. Now, the formula for urea is C 2 H 4 N 2 2 [CHiNaO], which is equivalent to two atoms of carbonate of ammonia minus two atoms of water (2NH 3 C0 2 ~ 2HO = C 2 N 2 H 4 2 ) L(H