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 QP145 .B28 The digestion and as 
 
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 BART LETT 
 
 STI AID ASSIMILATION OF FAT II 
 DY 
 
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 Columbia JBntomity 
 intljeCtiptiDtogtfrk 
 
 College of tPtjpsficfans? and burgeon* 
 
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 THE 
 
 DIGESTIOXAND^ASSIMILATION OF 
 EAT II THE HUMAN BODY. 
 
 AX EPITOME OF LABORATORY NOTES ON 
 
 PHYSIOLOGICAL AND CHEMICAL EXPERIMENTS BEARING 
 
 ON THIS. SUBJECT. 
 
 H. CRITCHETT, BARTLETT, PhJ)., F.C.S., 
 
 AUTHOR OP 
 
 ANALYTICAL PAPERS ON THE SUBJECTS OP FOOD AND THE NOURISHMENT OP THE BODY 
 
 IN '• THE LANCET," " THE BRITISH MEDICAL JOURNAL," 
 
 "THE MEDICAL PRESS AND CIRCULAR," "THE MEDICAL RECORD," 
 
 "THE SANITARY RECORD," ''PUBLIC HEALTH," ETC. 
 
 HEW YORK 
 
 LONDON: 
 J. & A. CHURCHILL, NEW BURLINGTON STREET. 
 
 1877. 
 
THE 
 
 DIGESTION AND ASSIMILATION OF 
 FAT IN THE HUMAN BODY. 
 
 AN EPITOME OF LABORATORY NOTES ON 
 
 PHYSIOLOGICAL AND CHEMICAL EXPERIMENTS BEARING 
 
 ON THIS SUBJECT. 
 
 H. CRITCHETT, BARTLETT, PhJX, F.C.S., 
 
 AUTHOR OF 
 
 ANALYTICAL PAPERS ON THE SUBJECTS OP FOOD AND THE NOURISHMENT OF THE BODT 
 
 IN '• THE LANCET," " THE BRITISH MEDICAL JOURNAL," 
 
 " THE MEDICAL PRESS AND CIRCULAR," " THE MEDICAL RECORD," 
 
 " THE SANITARY RECORD," " PUBLIC HEALTH," ETC. 
 
 LONDON: 
 
 J. & A. CHURCHILL, NEW BURLINGTON STREET. 
 
 1877, 
 
6 
 
CONTENTS. 
 
 rim 
 
 Iktroducthw ... ... ... ... . . # 5 
 
 CHAPTER I. 
 
 A Brief Account ef the Circumstances, Experiments, and Con- 
 siderations leading to what is believed to be an Elucidation 
 of the Digestion and Absorption of Fatty Matters ... 9 
 
 Description of some of the Reactions and Functions of Pancreatic 
 
 Fluid ... ... ... ... ... ... 10 
 
 Analytical Processes for the Separation of the Active Principles 
 
 and other Components ... ... ... ... 14 
 
 The Fermentative Nature of the Pancreative Principles ... 19 
 
 The Emulsifying Power of the Pancreatic Fluid ... ... 22 
 
 The Manner in which a New Principle is thought to have been 
 
 Detected and Confirmed ... ... ... ... 26 
 
 CHAPTER II. 
 
 3iology and Che 
 reliminary Digestion of Fats ... ... ... 29 
 
 A Blight Sketch of the Physiology and Chemistry relating to the 
 
 CHAPTER III. 
 The Digestion of Fat in the Small Intestine ... ... 34 
 
 CHAPTER IV. 
 Artificial Aids to the Digestion of Fat ... ... ... 40 
 
 ADDENDUM. 
 
 Basly Evidence of the Commencement of Wasting Diseases dis- 
 covered bj the Excretion of Soluble Fat ... - • • *& 
 
THE DIGESTION AND ASSIMILATION OF 
 FAT IN THE HUMAN BODY. 
 
 INTKODUCTION. 
 
 Towaeds the autumn of 1872, a somewhat warm con- 
 troversy sprung up between the late Dr. Edward Smith 
 and myself, among others, respecting the proportional 
 nntriment and digestibility of certain articles of preserved 
 food, particularly in regard to "Australian meat" and 
 " condensed milk." 
 
 The numerous letters which appeared in The Times 
 and Standard, together with the more elaborate arguments 
 brought forward in the columns of several scientific 
 journals, attracted the attention of my esteemed friend 
 and teacher, Baron von Liebig. A very interesting 
 correspondence ensued, discussing minutely the various 
 questions at issue. 
 
 Among other valuable results, I may incidentally 
 mention the final repudiation by Liebig of the untenable 
 assumption that his own " extr actum carnis " was of a 
 food value bearing any close relation to the nutriment 
 contained in the whole bulk of meat from which it had 
 been extracted. This candid admission of mistaken 
 
6 THE DIGESTION AND ASSIMILATION OF 
 
 views, which were previously advanced with no little 
 firmness and pertinacity, exhibited a great mind rising 
 superior to every self-interest and prejudice. As a direct 
 consequence of our intercommunication, this was natu- 
 rally highly gratifying to me ; but it is as an instructive 
 example, which may be borne in mind by all scientific 
 writers, no matter how distinguished then' position, that 
 siK-h a recantation should be regarded.* 
 
 During the progress of the discussion, Liebig expressed 
 a wish that I should place myself in communication with 
 Drs. Playfair and Bence Jones. The former was away 
 from London at the time, and when in town was neces- 
 sarily absorbed by the cares of high official duties ; I there- 
 fore invoked the kindly assistance of the secretary of" the 
 Royal Institution. 
 
 Dr. Bence Jones advised that a number of experiments 
 on the digestion of food should be undertaken ; and, after 
 much consideration, wrote to me, suggesting the tabula- 
 tion of a very lengthy series of reactions, only to be at- 
 tained by a course of investigation extending over several 
 years. 
 
 The various proximate principles of food were to be 
 administered without any mixture with other matters, 
 except water. The reactions to be recorded were as to 
 acidity, neutrality, or alkalinity during each stage of 
 digestion, from the mouth to the lower bowel. Not only 
 was the food mass to be thus tested, but my far-seeing 
 adviser was still more interested in obtaining similar 
 indications respecting the different conditions of the 
 various digesting juices. They were to be taken just as 
 
 * A precedent so frank was not lost on Dr. Edward Smith, who in his 
 later writings also virtually admitted that he had entertained erroneous 
 views even on the main points of the controversy. 
 
HUMAN BODY. 
 
 secreted in their respective glands during the digestion of 
 each single component of food, the like observations being 
 registered before and after digestional activity. Even 
 beyond this, it was considered very desirable that the 
 muscular tissues surrounding the digestive organs should 
 be equally carefully tested, for reasons which I scarcely 
 understood the important bearings of at the time. 
 
 While the processes of digestion in life were to be 
 studied to afford the closest possible insight into the 
 laws which govern the solution and absorption of the 
 various food principles, the artificial digestion of tingle 
 components of food, to be afterwards supplemented by 
 simple combinations, was proposed to be experimented on 
 in the laboratory with a completeness I have not yet 
 been able to fully carry out. 
 
 Here was a programme ambitious enough, if affording 
 any promise of leading up to a thorough comprehension 
 of the true principles of the digestion of food, ho <v ever 
 complex in their alternations and combinatVns in the 
 living human economy. Dr. Bence Jon' s .vas tjtiite 
 persuaded that such a course of experimen s w Duld con- 
 tribute, at least, to the foundation of sucL I .*ow)edge, 
 and he was eager to obtain the information to be acquired 
 by this means. 
 
 I have so far quoted from such of his letters as I have 
 still by me. Whether he would have consider'.":! his 
 anticipations just ified by the progress since made, ■ can- 
 not presume to decide; but of this I am fully conscious, 
 that in losing the benefit of his co-operation, advice, and 
 encouragement, at his decease in the following year, 
 many of the immediate scientific deductions logically to 
 be drawn from the experiments made have been lost for 
 ever. 
 
8 THE DIGESTION AND ASSIMILATION OF 
 
 Unable to devote the whole of my time and the con- 
 siderable amount of money necessary to carry out the 
 proposed research in its integrity, and being now 
 hampered by the recent anti-vivisectional legislation, 
 it is improbable that I shall be able to complete the 
 physiological investigations commenced under such 
 favourable auspices. 
 
 Accident, however, conduced to forward one particular 
 train of experiments, namely, that on the digestion of 
 fat in the living body ; and as the artificial digestion of 
 fatty matters was undertaken contemporaneously, the 
 results have attained a greater advance than in any of 
 the other sections. I therefore intend to discuss in this 
 short treatise the general principles of digestion involved, 
 to that extent only which may be necessary to explain 
 their bearing in this instance. 
 
 For the last eighteen months I have had the valuable 
 assistance of Dr. G. Overend Drewry, whose collaboration 
 in the later physiological experiments has very materially 
 helped to work out some of the more interesting problems 
 connected with these peculiar digestional phenomena. 
 
FAT IN THE HUMAN BODY. 
 
 CHAPTER I. 
 
 A BRIEF ACCOUNT OF THE CIRCUMSTANCES, EXPERIMENTS, AND CON- 
 SIDERATIONS LEADING TO WHAT IS BELIEVED TO BE AN ELUCIDATION 
 OF THE DIGESTION AND ABSORPTION OF FATTY MATTERS. 
 
 The examination of the constituents of the gastric fluids 
 of the stomach forms naturally a leading feature of the 
 scheme proposed by Dr. Bence Jones. It was on that 
 score I was led to attempt the determination as to 
 whether the solvent power of pepsin upon the albumin- 
 ous portions of food is, or is not, accelerated and assisted 
 in its own function by admixture with other digestive 
 principles. This is broadly stated to be the case by 
 several American physicians ; and the advantageous use 
 of the active principles of the sweetbread, or pancreas, 
 in helping the pepsin of the gastric juice in the stomach, 
 is vouched for by a chemist of high standing in New 
 York. My inquiries somewhat corroborate these views, 
 but in carrying out the trials I was for a time altogether 
 foiled in the endeavour to obtain in a convenient form 
 that portion of the pancreatic juice which should consti- 
 tute reliable pancreatin. 
 
 I could purchase useful pepsin, at a high price it is 
 true ; and concordant results were obtained of its powers 
 of solution, even if the peptic solvent was almost 
 invariably below a fair standard. The pancreatin sold 
 at the shops, either as a powder or in a suspended state 
 in oil, proved, on the other hand, so unequal in its action 
 as to disturb all parity of experiment. If I had been 
 dependent upon any of the samples of prepared pancreatin 
 I was able to procure from our best known English 
 
10 THE DIGESTION AND ASSIMILATION OF 
 
 druggists, I should have been compelled to relinquish all 
 further research, not only as to its supplementary action 
 to pepsin, but in regard to its own specific functions. 
 
 Yery little can be said in excuse for the manufacturers 
 of the so-called pancreatin, who put forward, as the true 
 active principle* of the pancreatic juice, preparations 
 which rarely contain one-tenth part of the active principles 
 to be found in the solid contents of that fluid. But what 
 can be the word which will express the confidence in the 
 want of knowledge of patients and want of testing by 
 prescribers, or the unconsciousness of their own ignorance, 
 which permits the sale of preparations termed pancreatin 
 yielding less than 2 per cent, of any active principle of 
 the fluid, and in some instances show none whatever? 
 These last and utterly worthless samples have been more 
 frequently sent to me than the unreliable preparations 
 first alluded to, which do contain just sufficient of the 
 active principles to cover the inertness of more than nine- 
 tenths of their bulk. 
 
 At the outset, however, I determined to rely only on 
 preparations made with my own hands; the hindrance 
 occasioned by the bad pancreatin supplied from the shops 
 was so far fortunate, inasmuch as it induced me to imme- 
 diately devote a special attention to these experiments, 
 instead of proceeding with them merely as supplemental 
 to those commenced on pepsin. 
 
 Description of some of the Reactions and Functions of 
 Pancreatic Fluid. 
 
 We could scarcely expect very close accord in the 
 earlier observations respecting the reactions of the pan- 
 
 * It is noticeable that " the active principle" is always printed on 
 the labels of the preparations in the singular. 
 
FAT IN THE HUMAN BODY, 11 
 
 creatic fluid. At a period of scientific research, J owever 
 brilliant, when the dispute "raged furious" be^re the 
 savants could decide the nature of th gastric ac :.';••, it is 
 not surprising to find the pancreatic mice desc"' bed as 
 acid, acid-saline, neutral, faintly alkali '.u\ and . trongly 
 alkaline. De la Boe and De Graf sta>:- it w?v- acid to 
 their tests and saline to their taste: Peel Jin an.i Brunner 
 compared the reaction to that of a neutral kait: Meyer 
 discovered the fluid from the pancreatic gland of a cat 
 to be faintly alkaline, which was corroborated by 
 Magendie. Tiedemann and Gmelin, taking the first 
 portion of fluid issuing from the pancreatic duct of a dog, 
 which was opened for the experiment, found it to be 
 slightly red and turbid ; it was put aside without testing 
 for some time. The next portion was whiter, with a 
 bluish cast, and was decidedly alkaline, being con- 
 sidered the unmixed fluid from the gland. On reverting 
 to the first portion, the test paper showed distinct acidity. 
 
 Baron Lucicn Corvisart, the eminent medical adviser of 
 the late Emperor of the French, referring to the previous 
 experiments of Pappenheim, asserts that in one of ita 
 functions, namely, its digestion of fibrinous albuminoid 
 matter, the action proceeds whether the fluid is in an 
 acid, neutral, or alkaline condition. 
 
 With all the apparent contrariety of the reactions thus 
 recorded, Corvisart's experiments are mot sufficiently 
 conclusive to hold good with regard to the reactions proper 
 to the other functions of the pancreatic fluid. Leuret 
 | and Laasaigne, however, afforded the first reasonable 
 explanation of the former seeming inconsistencies of re- 
 al by proving that, when freshly exuding at the 
 A of intestinal digestion, the fluid is always strongly 
 alkaline in health : that shortly after its escape into 
 
12 THE DIGESTION AND ASSIMILATION OF 
 
 any receptacle not protected from the air it becomes 
 neutral, and after some time it turns acid. 
 
 Notwithstanding the valuable experiments of Bernard 
 during the lengthy investigations he has bestowed on the 
 subject, I propose to tread on almost virgin ground in 
 the endeavour to identify with each peculiar function 
 of the pancreatic fluid the characteristic reaction most 
 suitable for the development of its activity. 
 
 In as few words as possible, I will give a short account 
 of the different functions displayed by the combined 
 principles contained in this complex digestive. 
 
 Bouchardat and Sandras demonstrated that raw starch, 
 which remained untransformed in its passage through 
 the gizzards of birds, and through the stomachs of those 
 animals where the saliva is insufficient to change all the 
 starch swallowed, is powerfully acted on in the intestine 
 as soon as it is in contact with the pancreatic fluid. The 
 corpuscles are eroded, dissolved, and transformed into 
 sugar. Such digestion and chemical change involves the 
 hydration of the starch by its taking up an exact 
 equivalent of water ; this is proved in the artificial action 
 on starch by the pure active principle of the pancreatin 
 when it is separated from its congeners, glucose being tlr 
 result. 
 
 I find, when working with the pure principle o^ 
 pancreatin which transforms starch, this action m 
 favoured by distinct alkalinity at first, passing by! 
 degrees through the two other stages of neutrality and 
 acidity. Sugar is formed out of the starch from the very! 
 first, and if the artificial transformation is conducted at a 
 low temperature, not much above 65°, by the time the 
 fluid becomes decidedly acid the chemical change will be 
 effected without putrefactive decomposition. A heat 
 
FAT IN THE HUMAN BODY. 13 
 
 e( }ual to that of the body, when the pancreatic sugar- 
 arming principle is not accompanied by antiseptics 
 s .milar to those furnished by the gastric fluids and the 
 ■jile, causes too rapid a change from alkalinity to strong 
 cidity to convert the whole of the starch, before it 
 .evelops large quantities of lactic acid, and putrefactive 
 <// ; sorganization sets in. 
 I My experiments included the use of many antiseptics 
 to simulate in the laboratory the processes of nature in 
 ^he living body. The result of employing the stronger 
 /'antiseptics, in quantities sufficient to prevent putrefaction, 
 (was, I found, equally fatal to the active principles! 
 (Those of a lesser astringency, with certain exceptions, 
 'proved themselves less competent to delay putrescence 
 'than to arrest the functional power of the pancreatic 
 principle. No foreign antiseptic enabled me to dispense 
 with the natural preservatives of the bile and gastric 
 fluids ; but with these, or rather with a portion of these, 
 as I shall hereafter explain, I obtained the transforma- 
 tions by the proper principles of the pancreatic juice at 
 temperatures approaching that of the living body, and 
 without putrefactive evidence. 
 
 The peculiar principle of pancreatin, exercising diges- 
 tion al power over nitrogenous substances, comports with 
 the functions previously noticed by Corvisart, except 
 that this principle, when separately used, instead of 
 taking the concrete fluid for the purpose, is infinitely 
 more energetic in a state of acidity. 
 
 Two special digestive actions of pancreatic juice having 
 been separately watched in their somewhat opposite 
 capacities, and the reactions most suitable to each 
 individual principle ascertained, a third, by far the most 
 essential of all the specific functions of the fluid secreted 
 
U THE DIG ESTION AND ASSIMILATION OF 
 
 by the pancreas, remains for investigation, namely, ( 
 principle effecting the digestion of fat and oi] 
 
 As this portion of the pancreatic jnice has not he 
 tofore been even indicated, although its presence 
 acknowledged at all hands, and as It forms he ma 
 subject of this treatise, I mnst leave to the narration 
 my experiments snch description as may be the o{ 
 come of long-continued labonr to advance this subject 
 
 Before entermg npon detail, it is essential to be umh 
 tood that, when I have nsed the word pancreatin, I ha 
 so designated the combination of active princip es co 
 tamed in the pancreatic flnid, which may be presented 
 a dry bnt perfectly solnhle form. Theword^nT toe 
 obee .enable, as it appears to refer to some sT„! 
 
 at least three dnferent active agents, each performin 
 distinct and even opposite functions. The taJp^S 
 
 mafterSr'^r^, " ^^/pancrea 
 matters soluble n water, insoluble in alcohol, and coa ff u 
 lablc by heat, that it must still do duty for the crud 
 aohds of the pancreatic fluid, which ha™ been dr e 
 without mjury to their solubility or digestional action 
 
 Analytical Processes for the Separction of the Active 
 Principles and other Components. 
 Keviewing the causes which in all probability contribute 
 to render the pancreatin of the shops so poo/a digestive 
 ^occurred to me that the fluid taken in L first Lt2 
 may not have been procured when the glands were 
 
 secreting strong solvent principles. Several efpenW,7terc 
 have remarted that the max . mum P enters 
 
 of the pancreatic juice can only he acquired by rem vhig 
 the pancreas of smtable animals immediately after deatff 
 
FAT IN THE HUMAN BODY. 15 
 
 when digestion of food containing fat has commenced 
 from three to seven hours previously. My own experience 
 points to the superiority of the fluid obtained as it flows 
 through the pancreatic duct at that period of digestion, 
 but I found in practice a larger quantity is at once drawn 
 from the gland, taken during vigorous digestion, if it is 
 instantly subjected to maceration. 
 
 Difficulties were thrown in my way by the butchers 
 and slaughtermen to whom I applied for sweet! >i 
 from the animals under the necessary conditions. I was 
 assured that all the pigs, calves, and other beasts killed 
 for food are previously fasted so long that the upper 
 intestines are always empty. This is regarded as of 
 great importance by the butchers ; but as, when fasting, 
 the pancreatic glands only furnish fluids yielding the 
 smallest proportion of active principles, the scruples of 
 the slaughtermen had to be overcome. 
 
 At length I succeeded in procuring an occasional porcine 
 pancreas, which I could depend upon being extracted 
 from the carcase as I desired, but it could only be relied 
 on in this respect when the chyle in the intestine was 
 verified by ocular demonstration. 
 
 The pancreatic glands were passed through one of 
 Nye's masticating machines until effectually pulped ; 
 this magma being exhausted by successive washings 
 with distilled water at 40° F., was filtered at that 
 temperature to prevent the least decomposition. The 
 natural healthy secretion, as it flows through the 
 pancreatic duct, contains about 9 per cent, of solids. 
 These are composed of albuminoid mutter soluble in wate ', 
 albuminoid matter not soluble in alcohol, fatty matter, 
 extractive matters and salts soluble in alcohol, together 
 with other salts, chiefly of sodi in. All these couip<>> 
 
16 THE DIGESTION AND ASSIMILATION OP 
 
 were found in the pancreas, the fatty constituent being 
 immensely larger than in the exuding fluid. The watery 
 extract was then subjected to several methods of analysis 
 to separate, as far as possible, not only the constituents 
 named, but to attempt the isolation of the various active 
 principles. 
 
 Organic matter dissolved in the watery extract is 
 largely precipitable by alcohol, and to that extent, while 
 retained in solution, is exceptionally liable to putrefy at 
 temperatures above 40°. In this respect it resembles in 
 a major degree some of the extractives of the saliva, but 
 this unstable condition marks an essential divergence 
 from the extractives of the gastric juice, which seem 
 always combined in their first watery solution with an 
 antiseptic which preserves them. 
 
 Such nitrogenous matter as is thrown down by strong 
 alcohol resembles albumin us substance in composition. 
 That which remains when the alcoholic solution aftei 
 filtration is evaporated, and the residue washed withl, 
 ether, is a pale yellow curdy substance. 
 
 Still more minute subdivision can be effected by 
 other and more complex methods of precipitation ; after 
 which, the matters separated, though consisting of or 
 containing the true active principles of the original fluid, 
 can only be allied to ordinary albuminoid matter, as they 
 do not react with most of the common tests for albumin. 
 
 Some of the more advanced foreign chemists have 
 proposed several systems of very delicate separations, by 
 which they claim to have produced two of the active 
 principles of the pancreatic fluid, each being of great 
 purity. The descriptions of the reactions said to accom- 
 plish these results having been submitted to me only by 
 notes, certain discrepancies and a semblance of contra- 
 
FAT IN THE HUMAN BODY. 17 
 
 diction, so conveyed, might be removed, and the precise 
 modus operandi rendered clearer if more minute details 
 were afforded. 
 
 Acknowledging the advantage of having other minds 
 working with the same object, I have not hesitated to 
 modify the suggestions as they came to me, when in 
 following them to the" best of my ability I have not met 
 with the expected results. 
 
 The aqueous solution of pure pancreatic fluid should be 
 taken while strongly alkaline ; or if the watery extract is 
 filtered from the pancreas, the gland may be previously 
 rubbed up with magnesium carbonate, to over-neutralize 
 any acidity liable to be acquired during the long time 
 necessary for the extract to pass through the filter paper. 
 Into this, as my correspondent states, "the transparent 
 colourless jelly, produced by mixing nitric acid sp. g. 1*5 
 with starch, is thrown. The instant it reaches the 
 aqueous extract a white insoluble precipitate is formed, 
 carrying down with it the active principle which digests 
 fibrinous matter.'' The solution can then be filtered off, 
 and the insoluble precipitate redissolved in weak nitric 
 acid, leaving the active principle pure." The possibility 
 of success by this method evidently depends upon the 
 correctness of the assertion that the principle carried 
 down in the precipitate is unaffected by nitric acid. 
 
 'treating the aqueous extract in the same way, I sjib- 
 Ktituted for the nitrated starch a solution of the less 
 highly nitrated pyroxylin in ether-alcohol, which, while 
 precipitating out with it the fibrin-digestive principle of 
 pancreatin, leaves the starch-transforming agent in the 
 
 * The peculiar principle of the pancreatin fluid which digests nitro- 
 genous matter ia proportionally far more energetic in dissolving fibrin 
 albumin. 
 
13 THE DIGESTION AND ASSIMILATION OF 
 
 solution. This may be filtered off, and evaporated at a 
 low temperature. The latter separation produces with 
 certainty an almost colourless powder, absolutely inert 
 as a solvent of fibrin, but a powerful starch converter. 
 I greatly prefer the use of pyroxylin for the isolation of 
 this particular principle, for I must confess I failed to 
 reach this result by means of the nitrated starch. 
 
 If this method of analysis can be extended by redis- 
 solving the double precipitate, so that the fibrin-solvent 
 is obtainable from a mixture of ether and water, it 
 will greatly add to the value of the process, supposing we 
 need not depend upon excessive nicety of manipulation. 
 According to my own experience, however, I prefer ex- 
 tracting the fibrin-solvent free from the starch -transform- 
 ing principle and all other extraneous matter by pre- 
 cipitating with calcic phosphate, which can be readily 
 conducted with the necessary accuracy. 
 
 A naturally neutral watery extract should be taken 
 from the gland ; that is to say, the usual alkaline extract 
 is allowed to stand until it has become exactly neutral. 
 Sufficient tri-basic phosphoric acid is thrown in to make 
 up the whole to a solution of one in twenty. It is then 
 slightly over-neutralized with a known quantity of lime 
 in water ; to which the precise equivalent of phosphoric 
 acid is added to produce an insoluble bi-calcic phos- 
 phate, from which the fibrin-solvent can be washed with 
 distilled water. 
 
 Other methods of isolating these two active principles 
 give results similar in all essentials to the solvents 
 yielded by the foregoing analytical processes. The sub- 
 stantial truth of the propositions involved is thus con- 
 firmed, and we can now class these peculiar agents and 
 their reactions as known principles, producing well-defined 
 
FAT IN THE HUMAN BODY. 19 
 
 and characteristic organic change in those matters which 
 are appropriate to each, and in no other kind of matter. 
 
 Recent research abroad appears to corroborate the 
 earlier determinations of these experiments, but respecting 
 the exact nature of the stimulating action possessed by 
 such principles in effecting organic change, no general 
 consensus of scientific conviction is jet attained. My 
 endeavour is to deal with this portion of my subject as 
 tentatively as possible ; discriminating as far as may be 
 between assumed facts, credible theories, and the uncer- 
 tainties of both. My most important results must be 
 regarded to some extent by the light which can be thus 
 afforded ; it is therefore essential to their explanation. 
 
 The Fermentative Nature of the Pancreatic Principles. 
 
 The stimulating action of the principles contained in 
 the pancreatic fluid, as well as in all the other digestive 
 Excretions, is due to true fermentations produced by 
 
 em. These ferments must not, however, be considered 
 
 Ki strictly analogous to the alcoholic ferment of yeast ; 
 1 the contrary, we must try to discern the extent to 
 ihich their fermentative action differs from the better 
 fnown, and therefore more widely acknowledged, fer- 
 nents, so elaborately classified and described by Pasteur. 
 To illustrate more clearly the character of the fer- 
 ments forming the active principles of the pancreatic 
 md other digestive fluids, to those who have not made 
 a special study of the wonderful phenomena attending 
 upon the simplest and best known fermentation, namely, 
 Icoholic, I will explain the immediate connection 
 en the fermentation by yeast and the fermentation 
 by digestive principles. 
 
 06 sugar is not fermentable aa long as it retains 
 
20 THE DIGESTION AND ASSIMILATION OF 
 
 its composition is such — vide the text-books. Before it 
 can be acted upon by yeast so as to be converted into 
 alcohol and carbonic acid, a preliminary change must be 
 first induced; this is effected when the cane sugar 
 becomes hydrated and its composition is found to be 
 made up of glucose (grape sugar) and lsevulose (unerys- 
 tallizable sugar). The reagent producing this pre- 
 liminary change was discovered by Berthelot in the 
 water in which yeast has been washed, even after it 
 has been filtered perfectly 'free from any yeast cells. 
 From its peculiar action on cane sugar, it was termed 
 inversive ferment ; and Bechamp afterwards proved that 
 it consists of soluble nitrogenous matter, either extracted 
 from the yeast cells during their growth and repro- 
 duction, or excreted and thrown off in the process of 
 their development. 
 
 The most remarkable characteristic of this soluble 
 nitrogenous matter is the extraordinary rapidity with 
 which a very minute quantity of it in solution causes 
 the hydration of cans sugar. The peculiarity is strik-,, 
 ingly indicated by all the soluble nitrogenous fermenfej 
 principles excreted by the digestive organs; infinitely 
 small quantities producing the most important and! 
 prolonged reactions. 
 
 The same fermentative hydration splits up cane sugar' 
 into glucose and uncrystallizable sugar, converts starch 
 into glucose and dextrin ; and the glycerides (fatty 
 matters) become hydrated when split up into glycerin 
 and fatty acids in the presence of water. The group of 
 different albuminoid substances which composes the 
 complex soluble nitrogenous ferments may also be re- 
 garded as the result of the breaking up of ordinary 
 albumin by hydration. In this essential splitting up of \ft 
 
FAT IN THE HUMAN BODY. 21 
 
 the various constituents of food, and in their consequent 
 hydration, we observe the true action of the inversive, 
 soluble, and digestive ferments. 
 
 Whether the inversive soluble ferment be taken from 
 yeast-washing, or any of the digestive ferment principles 
 are isolated from the other constituents of the digestive 
 juices, all soluble ferments are produced directly from the 
 living organism. As long as the yeast plant lives, the 
 inversive ferment is freely given off in solution, except 
 when the presence of special antiseptics arrests this 
 excretion without killing the plant. Similarly, the 
 digestive glands of the animal body may secrete fluids 
 in which the soluble ferments arc rendered inert during 
 the period they are under the influence of counteracting 
 agents. 
 
 Boric acid at a certain strength of solution arrests the 
 vitality of inversive ferment and causes digestive fer- 
 ments to remain dormant until they are washed free 
 from its control. Alcohol has the same effect, varying 
 only with the amount of its dilution. Citric, tartaric, 
 acetic and many other acids, usually found in a dilute 
 form in food, exert a very injurious effect upon the 
 digestive ferments, if they mix with the digestive fluids 
 while too concentrated or in excessive quantities. 
 
 Some volatile oils, on the other hand, exercise very little 
 subduing influence on the solvent powers of the digestive 
 ferments, although many of them, especially the turpenes 
 (represented by oil of cloves, lemon peel, etc.), are highly 
 antiseptic in the prevention of putrefactive decom- 
 position. The volatile oils, which are themselves the 
 product of fermentation, appear rather to stimulate 
 digestion ; of this we have a good example in the volatile 
 principle of mustard. 
 
22 THE DIGESTION AND ASSIMILATION OF 
 
 A wide line of demarcation is thus revealed between 
 the direct ferments, complete in their own organism, like 
 yeast, and the indirect soluble ferments which are the 
 product of organism but are not so organized in them- 
 selves as to permit of reproduction ; and this is evidenced 
 by the opposite reactions produced upon the two different 
 classes of ferments by the antiseptics enumerated. 
 
 The Emulsifying Power of the Pancreatic Fluid. 
 
 Bernard was enabled to demonstrate that no othei 
 fluid secreted in the digestive organs, except that from 
 the pancreas, can produce the complete digestion of a 
 sufficiency of fats or oils. The remarkable property of 
 forming an emulsion by mechanically holding the fat 
 or oil in minute globules, with water filling up the 
 interstices, is almost alone possessed by this juice. I 
 am desirous of making an amendment to M. Bernard's 
 statement that the power of emulsion is altogether 
 peculiar to the pancreatic fluid, because I find that it is 
 also produced to a very much smaller extent by the 
 saliva. I am, however, completely in accord with the 
 observation that the after saponification is only at present 
 provable when oils or fats are subjected to the digestive 
 fluids of the duodenum. Without refining too much on 
 the possibility of a similar function perhaps appertaining 
 to the saliva, it is evident that, as a very slight saponi- 
 fying action is supposed to assist in conducting the fats 
 of food through the walls of the absorbents, a still more 
 minute agency of the same description may exist in the 
 saliva without our being able to perceive it. 
 
 The state of emulsion is beautifully apparent if a drop 
 from a sample of milk is placed upon the stage of the 
 microscope. The globules are found floating about in 
 
FAT IN THE HUMAN BODY. 23 
 
 that constant and rapid motion which takes place in all 
 similar matters devoid of organization, and is denominated 
 the Brownian movement. Without doubt, this movement 
 in the globules is essential to the persistence of a mere 
 mechanical emulsion; and although Mitscherlich and 
 Moleschott were able to show that, in milk, this emulsive 
 form is maintained by each globule of fat being coated 
 with a thin pellicle of albumin, I have noticed the larger 
 globules of butter, or those exceeding 2?V <J tn °f an mcn m 
 diameter, have a strong tendency to aggregate, on long 
 keeping, by the rupture of their albuminoid vesicles. 
 
 The Brownian movement is not so manifest in the 
 emulsion of the fats of food formed by the digestive fluids 
 in the intestine, but the globules are even smaller than 
 in milk. Emulsions are also sometimes formed which 
 certainly do not contain any appreciable quantity of 
 albumin, and these retain their form as long as others 
 containing even a good deal of albuminose. 
 
 What is the peculiar principle, conveyed in the 
 /pancreatic fluid, which has so powerful an emulsive 
 action ? To this I can only reply that I have repeatedly 
 : found pancreatic fluid which both converted starch into 
 / glucose, and fibrin into peptone, but was extremely inert 
 in the digestion of fat. In these cases, I have invariably 
 noticed that the pancreatic glands were deficient in the 
 ( very peculiar fatty constituents of which they are so 
 I largely composed when taken from a healthy animal. 
 The inference deducible from this fact is that the 
 ferment prinr-iple producing instantaneous and perma- 
 nent emulsion in the fata of food, is itself of a fatty 
 . or is carried by or dissolved in fat or oil. 
 le other experiment corroborates this assumption, 
 , .lamely, if we take the other pure principles of the 
 
24 THE DIGESTION AND ASSIMILATION OF 
 
 fluid absolutely free from fat, we find the wonderfully 
 vigorous emulsifying property is almost destroyed. 
 
 A great misconception as to the real characteristics of 
 a true pancreatic emulsion has been entertained by many, 
 and but few appear to have studied the different aspects 
 presented by such an emulsion a3 is produced on fat by 
 the energetic action of pure soluble pancreatin, as con- 
 trasted with the coarse mechanical mixtures of oil or fat 
 and water which are commonly supposed to represent this 
 function of fermentative digestion. 
 
 Some seem to think that if a bottle of oil is shaken up 
 with the compounds sold as the active principle of the 
 pancreas, and a yellowish cloud is diffused for a time 
 through the oil, an emulsion has been obtained. So it has, 
 but not the true pancreatic emulsion, which forms an 
 integral portion of the process by which fats are digested 
 and assimilated. From the unvarying result of many 
 hundred trials with the pure, active principles of healthy 
 pancreatic fluid, taken at the time of digestion, I am 
 perfectly convinced that no valuable result has been 
 attained unless the emulsion formed is as highly refrac- 
 tive of light as milk. The colour may vary, according to 
 the oil or fat used, from a far whiter fluid than the 
 densest milk to the opacity and colour of Devonshire 
 cream ; but unless at least the equivalent of the density 
 of the best milk is produced in oil, when a third of water 
 is held in suspension, no real pancreatic emulsion has 
 been formed. 
 
 The mere mechanical mixture formed by common 
 pancreatin is rarely better or more persistent than may 
 be produced by rubbing up oil or fat with a solution of 
 mucilage, or by a warm application of dissolved gelatin 
 shaken with oil until it becomes cold. 
 
FAT IN THE HUMAN BODY. 25 
 
 The first essential towards the digestion of fat or oils 
 in the human body is that it shall assume the state of the 
 very finest and most permanent emulsion, and this is only 
 known to be attained when the oil and water is perfectly 
 opaque, from the minuteness of the globules. This is 
 the first function of the pancreatic emulsifying principle, 
 and by this alone can we be certain that it possesses its 
 proper fermentative activity. 
 
 The Manner in which a JVeio Principle is thought to 
 have been Detected and Confirmed. 
 
 Proceeding systematically in the examination of the 
 various separate ferment principles given out by the 
 healthy pancreatic gland, when in the greatest activity, I 
 arrived at the unavoidable conclusion that the reaction 
 proper to the exercise of all their functions in combina- 
 tion is that of alkalinity. The alkaline fluid produces 
 the perfection of emulsion described, but no chemical 
 change is effected in the fatty matters of food by the 
 pancreatic fluid alone, except after a lapse of time which 
 it is inconsistent to suppose can be accorded in the 
 intestine. Bernard believed that the slight saponification 
 is perhaps commenced in the intestine, and then con- 
 tinued in the after processes of absorption. This latter 
 proposition is not borne out by my experiments ; the fat 
 in contact with the pancreatic fluid, the bile, and 
 intestinal juices in the bowel, being more evidently 
 : lined than the oil in the villi, the lacteals, or in the 
 blood. How far this may bo assisted by the alkalies and 
 other reagents of the bile and fluids from the intestinal 
 jlands, I will not wait here to discuss ; merely recording 
 ,eI ny persuasion that the reactions induced by their means 
 
36 THE DIGESTION AND ASSIMILATION OF 
 
 are of the very essence of the digestion al changes of fat 
 which enable it to be absorbed. 
 
 My attention being engaged more particularly in 
 separating the principles and in identifying their peculiar 
 functions, I had only arrived at the negative result before 
 mentioned — namely, that the further chemical change of 
 the fatty emulsion is probably not due to the pancreatic 
 fluid alone — when, in manipulating the pancreas of a pig, 
 I almost stumbled on what appeared to me a startling 
 discovery. 
 
 After obtaining the watery extract from the gland, the 
 strongest alcohol (not absolute) was added to precipitate 
 the coagulable albumin. When this was poured off and 
 evaporated, I found a peculiar greasy deposit. At first, 
 I was disposed to attribute this to the fineness of the 
 emulsion of fatty substance permitting it to pass through 
 the filter paper; but on repeating the experiment, I 
 obtained an almost bright filtrate of the aqueous solution, 
 and the alcoholic extract became perfectly clear and 
 brilliant. The deposit of grease was evidently not due 
 to the fineness of emulsion, for the finer the particles 
 of fat, the more opaque the milkiness would appear. I 
 therefore treated the deposit with ether, carbon- 
 disulphide, light spirit of petroleum, and other solvents 
 of fats and oils. 
 
 Every successive test showed the ease with which the 
 fatty portion was taken up by these menstrua, precluding 
 the possibility of its being mainly composed of the 
 glycerin liberated by the saponification of the fixed 
 f.itty acids forming the fat of the food previously given 
 i the pig. 
 
 When I first saw the pig, it had been fasted for forty- , 
 eight hours ; a meal of boiled potatoes mixed with beef 
 
FAT IN THE HUMAN BODY. 
 
 6uet was then given. Six hours afterwards the pig was 
 killed, and the pancreas submitted to the processes 
 alluded to. Yet here was a considerable quantity of a 
 brownish oil, to some extent volatile, or at least diffusible 
 at temperatures very little exceeding that of the body. 
 Extremely soluble in a very small proportion of ether, it 
 combined with the hydrates of sodium and potassium at 
 the higher degrees of animal heat — a result worthy of 
 note, as I am not aware of any previously known con- 
 dition of change in the fixed fatty acids which produces 
 soap at less than 176° F. 
 
 Control over the feeding of the pig for a period of 
 fifty-four hours appears adequate to assure us that the 
 glycerides of fatty acids, volatile at an animal heat, 
 were not contained in the immediate constituents of the 
 food recently given. 
 
 Absolute proof of this was desirable; so a portion of 
 the same sample of suet was taken, treated with potas- 
 sium hydrate and alcohol, and yielded a perfectly 
 bright solution of soap. It was then decomposed with 
 a mixture of hydrochloric and lactic acids, these being 
 found in the stomach of the pig. After well washing with 
 boiling water and drying in vacuo, 95*6 per cent, of 
 I fatty acids remained, leaving, if the due proportion 
 of glycerin be reckoned, no room for any trace of gly- 
 cerides of volatile fatty acids in the suet before the pig 
 ate it. 
 
 The obvious conclusion to be drawn from this extra- 
 ordinary result is that the animal digestion of fats and 
 oils' renders a certain portion of the fixed fatty acids 
 soluble in water and alcohol, and in a mixture of both. 
 If* this is correct, as is attested by all my after experi- 
 .to, the process of absorption of fat through the 
 
28 THE DIGESTION AND ASSIMILATION OF 
 
 membranes of the villi of the intestines and the other 
 absorbents is capable of another explanation besides 
 that doubtfully assigned to the slight saponification also 
 observed. 
 
 As a short summary of the results of these preliminary 
 experiments, I may state : — 
 
 Firstly, that the formation of even the most perfect 
 emulsion of fat or oil with water does not of itself 
 render any portion of the oil or fat soluble in water, nor 
 does the fat or oil take up any water, except mechanic- 
 ally, to become, so to term it, hydrated. 
 
 Secondly, the addition of alkalies to fixed oils or fats at 
 common temperatures, whether the alkalies are as hydrates 
 or salts, does not affect such transformation. 
 
 Thirdly, mixtures of fixed oils or fats with water and 
 the solids of the pancreatic fluid, when kept for long- 
 periods, promote the separation of the fatty acids from 
 the glycerin. This decomposition is, however, effected 
 by that most disgusting butyric fermentation, which is 
 set up in the presence of putrefying nitrogeneous matters 
 supplied by crude pancreatin, and is never found in a 
 healthy state. 
 
 Fourthly, saponification is not the only natural solu- 
 tion of fatty matters in water at the temperature of the 
 body. 
 
 Fifthly, that fatty matters are found in the pan- 
 creatic fluid and in the pancreas in a free state; in 
 solution with water (hydrated); and are also slightly 
 saponified in the intestine. These, or some of these 
 different forms of fat, are distinguishable in combinations 
 of various proportions in the intestine, the pancreatic 
 gland, the thoracic duct, and while the fat or oilj is. 
 passing through the walls of the absorbents. 
 
FAT IN THE HUMAN BODT. 29 
 
 OHAPTEE IT. 
 
 A BLIGHT SKETCH OF THE PHYSIOLOGY AND CHEMISTHY RELATING TO 
 THE PBELIMINAHY DIGESTION OF FATS. 
 
 When fat or oil is taken in food or with food, as I am 
 led by the whole course of these investigations to believe 
 it always should be, the first introductory step towards 
 its digestion is effected in the mouth by all animals 
 possessing the instinct to thoroughly masticate their 
 food. I am aware that this is contrary to the generally 
 received teaching, which only acknowledges the chemi- 
 cally digestive action of the saliva on starch. In a 
 subsidiary degree, the valuable results of good masti- 
 cation are admitted, so far as appertains to the preparation 
 of the nitrogenous portion of food for the stomach. I 
 wish to claim the possibility of something more than this 
 being effected during the chewing, mixing, and incorpo- 
 rating to which the separate fatty matters taken in an 
 ordinary meal are subjected prior to being swallowed. 
 The presence of the alkaline fermenta of the saliva pro- 
 duces a coarse emulsion, which, when the other portions of 
 food are easy of chymification, is not altogether destroyed 
 _by the action of healthy gastric juice. Observations 
 founded upon experiments with dogs do not enable this 
 to be properly shown, as these animals seldom masticate 
 food of this character. 
 
 Many years ago, Dr. Wright announced that the degree 
 of alkalinity of the saliva during digeHtion was in direct 
 proportion to the acidity of the stomach fluids. Of the 
 precise accuracy of this I am by no means convince I, 
 although I niust endorse JJr. Bence Jones's observation 
 
30 THE DIGESTION AND ASSIMILATION CF 
 
 that, during the excretion of acid in the stomachic diges- 
 tion, the alkalinity of the other fluids is increased. I 
 take it that this means the total alkalinity of all the 
 other fluids is increased to the extent of the acid with- 
 drawn from them by the local digestion in the stomach. 
 
 The variation of acidity in the gastric fluid certainly 
 produces a marked difference in the appearance iu the 
 stomach. In the case of a meal containing hard, indiges- 
 tible, or irritating matters, the peptic solvents are found 
 highly charged with acid, and in the absence of sufficient 
 saliva, the fatty substances are seen separated from the 
 chyme, but pass through the pylorus at the same time in 
 a melted or oily form.* If the other components of the 
 meal are easy of chymifieation, the emulsion of fat by a 
 full quantity of healthy saliva is generally sufficiently 
 maintained against the feebler acids which are furnished 
 by the stomach to undertake the lighter task of trans- 
 forming the freely digestible albuminoids into peptones. 
 
 Fats or oils taken into the stomach without any other 
 food are usually swallowed rapidly ; they are, therefore, 
 less acted on by the saliva. The after flow of saliva 
 is also less abundant; this may result from the absence 
 of the muscular play upon the glands incident to the 
 masticatory action, or from the want of that sympathy 
 which, excites the outpour of this fluid after the savour 
 of the other principles of food has been appreciated by 
 the palate. Be this as it may, fatty matters or oils, taken 
 by themselves into the empty stomach, are less emulsified 
 by the ptyalin of the saliva and the oral mucus, and 
 are more distinctly separated by the'Stomach juices than 
 
 * When the acidity of the stomach is provoked to excess, no amount 
 of alkalinity which can be conveyed by the saliva will obviate the 
 separation of the fats. 
 
FAT IN THE HUMAN 30DT. 31 
 
 when they form part of mixed meals. In the same way, 
 the peculiar emulsionary function of pancreatin is ren- 
 dered nugatory when oil or fat is not accompanied with 
 other 6olid food. A fully pancreatized oil or fat may 
 sometimes pass through the stomach by itself without 
 being thrown out of emulsion, and in this form, if there 
 is a normal flow of bile, it may be, and probably is, ren- 
 dered easier of digestion. The reactions of the stomach 
 juices are, however, almost invariably acid enough to 
 separate the oil from the emulsion if no other food is 
 present to absorb the gastric fluids. 
 
 By tying the pylorus before any portion of the mixed 
 contents of the stomach can pass through, the progress of 
 chymification and stomachic digestion may be watched 
 with advantage. The pultaceous mass is not found to 
 be uniformly acid, neutral, or alkaline. For the first 
 hour or more, different portions exhibit these several 
 conditions. Neither the flow of alkaline saliva nor of 
 acid gastric juice is altogether continuous, observation 
 lending to the conclusion that their influence on some of 
 the food in the stomach is frequently alternative. The 
 maintenance of fatty evulsion, however, depends almost 
 entirely upon the alkalinity retained in it being at least 
 equivalent + o any acidity with which it comes in contact. 
 
 After fasting for forty-eight hours, fat or oil may be 
 kept in the stomach for several hours by closing the 
 pyloric orifice, without any increase being found in the 
 of fat usually contained by the surrounding lym- 
 phatics. The addition of a very small quantity of bile 
 and pancreatic juice to the fat in the stomach, however, 
 enriches the lymph taken from the thoracic duct in the 
 tice of chyle, until it yields nearly one per cent, of 
 fattv and other matters soluble in ether. 
 
32 THE DIGESTION AND ASSIMILATION OF 
 
 This would appear to show that a very limited but 
 rapid digestion of fat may, under certain circumstances, 
 take place in the stomach, and that it may be absorbed 
 there and enter directly into the circulation. The pro- 
 bable capacity of the lymphatics for carrying fat may 
 perhaps be claimed from the comparative analysis I was 
 enabled to make of the vascular glands of two hedgehogs ; 
 one killed just before hibernation, the other being re- 
 served until after that period. Both were of the same 
 age, and as nearly as possible of a size. The thymus 
 and appended fat glands, connected only with the blood 
 vessels and lymphatics, and with no direct communication 
 with the lacteals, became literally overcharged with fat 
 before the winter sleep, and 67 per cent, of fat in the 
 dried substance was extracted with ether. Whereas, 
 after hibernation, only a bare trace of fat was discover- 
 able in the similar glands of the sleeper when first 
 awakened by the approach of spring. 
 
 The distribution of fat by the lymphatic system, if this 
 can be admitted, affords a slight clue towards assisting 
 our comprehension of certain otherwise unaccountable 
 physiological facts. • 
 
 It is well known that the body of a well-nourished 
 adult contains nearly one-fourth of its weight of fat. 
 Equally well ascertained is the chemical truth that the 
 entire blood in circulation does not yield one-thousandth 
 part of the fatty components of such a body.* The 
 natural inference would therefore be that the elimination, 
 use, and waste in the human economy of life must be 
 particularly slow and small in quantity. The exact 
 reverse is, however, the case, as in starvation or wasting 
 
 * A man of eleven stone should have about 28 lbs. of fat and 12 lbs. 
 of blood in Ms body, which contains about $ oz. of fat. 
 
FAT EN THE HUMAN BODY. 33 
 
 of the bodily tissues, the -whole of the fatty structures are 
 reduced more rapidly and to a greater extent than in any 
 of the other tissues or juices. 
 
 Before death from want of food occurs, as much as 90 
 per cent, of the bodily fat is starved out; and it is a 
 noteworthy corollary to observe that, next to the fatty 
 tissues, the pancreas, salivatory, vascular, and other glands 
 lose the largest proportion of their substance, namely, 86 
 per cent., from the same cause ; these include the whole 
 of the fat-storing and digesting organs. 
 
 If it is difficult to understand how the blood can convey 
 all the fatty matters to their destinations so as to supply 
 the large and rapid daily waste, is it not feasible to believe 
 that the direct circulation of the blood may be supple- 
 mented by the fat-carrying capacity of the lymphatics ? 
 
 However small the power of digesting fat in the 
 stomach may be, it seems likely to afford, artificially, the 
 most rapid means of recuperation after great wasting of 
 the fatty tissues ; assisting the resuscitation of functional 
 activity of the natural fat-digesting organs. Certainly 
 the main hope of nourishing the pancreatic and other 
 digestional glands, so that their specific powers may be 
 stimulated, depends upon the conveyance to these organs 
 of that constituent fat which they are unable to take up 
 for themselves. 
 
 To assist this supplementary action of the absorbents, 
 or, rather, to enable lymph to take up fat at all, the one 
 absolute necessity, apparent to me by direct experiment, 
 is the perfect solubility of a portion of the fat or oil in 
 the w tigtituent <>f the lymph, minute though it be. 
 
 Pure lymph, as we know, is quite clear and devoid of 
 milkiness, even to the minimum extent indicated by 
 opeleeoence. After fasting from food for some time, the 
 
34 THE DIGESTION AND ASSIMILATION OF 
 
 thoracic duct contains transparent lymph only. Yet. 
 when the pylorus is tied, previous to a meal being given 
 in which fat is contained, the increase of fat to be found 
 in the thoracic duct does not cause, in the slightest degree, 
 the characteristic milkiness of chyle absorbed through the 
 lacteal s. In other words, this lymphatic -absorption of 
 fat, which is proved by analysis, consists only of fat 
 soluble in the watery lymph.* This leads me forward 
 to the consideration of the manner in which any portion 
 of fat becomes truly soluble in water so that it may be 
 absorbed. 
 
 CHAPTER III. 
 
 THE DIGESTION OF FAT IN THE SMALL INTESTINE. 
 
 We are obliged to acknowledge that, with the highest 
 microscopic powers, we fail to find the faintest indication 
 of any pores or ducts in the recognized absorbents of the 
 intestine. The absorption of food by blood vessels is 
 apparently almost omnivorous, many substances in a 
 sufficiently subdivided form seeming to be taken up by 
 them ; in addition to which, solutions and gases of most 
 kinds are also freely received and mingle with the blood, 
 frequently without being assimilated. 
 
 * I am particularly anxious to avoid laying undue stress upon the 
 amount of fat digestible in the stomach or capable of being- carried by 
 the lymphatics. The first is, I am aware, but very small, the latter 
 being difficult of estimation. 
 
FAT IN THE HUMAN DODY. 35 
 
 The penetration of solid particles, such as the sharp 
 dust of charcoal, cannot, however, be regarded as absorp- 
 tion, being due to attrition forcing them mechanically 
 through the walls of the vessels. The true absorption of 
 liquids also depends upon their suitability to mix with 
 and afterwards form a portion of the blood ; and I have 
 proved by repeated experiments that no other kind of 
 fluid enters naturally into the circulation, although it may 
 be forced into it. 
 
 Fat is found in an average sample of blood to the 
 extent only of 1*5 per thousand, and this partly in a 
 soluble form and partly as serolin. Free, fixed, or uncom- 
 bined fat will neither mix with to form part of the blood, 
 nor will it in this condition pass inwards through the 
 walls of the vessels. A certain amount of a different kind 
 of fat is, however, retained in the blood, which only 
 becomes insoluble after exposure to the air ; this is pro- 
 bably excrementitious, or a residue accumulating from 
 the soluble fat which is precipitable from solution by 
 the salts of the alkaline earths, and particularly by 
 phosphate of lime. It resembles cholesterin, but melts 
 at a much lower temperature, namely, 97° F. This 
 peculiar fat is, 1 find, eliminated through the sebaceous 
 glands, as well as by the bowels. 
 
 The chief supply of fat to the blood is not by direct 
 absorption from the blood, but from the chyle trken up by 
 the lacteal*. During the active absorption of chyle 
 containing fat, the villi become whiter and more opaque, 
 and when the fat has been duly prepared by admixture 
 with bile, pancreatic fluid, and the juices of the Intestinal 
 glands, a portion of this fatty constituent may be traced 
 in the in pit helium. The columnar cells, here 
 
 and there, become filled with brilliant globules of oil, 
 
36 THE DIGESTION AND ASSIMILATION OP 
 
 which I have ascertained to be free oil, containing no 
 water or other constituents of the chyle. 
 
 The columnar cells are so small that 1600 of them 
 placed end to end only measure one inch, their diameter 
 being less than half this size ; the value of the most per- 
 fect emulsion is therefore evident, by which only minute 
 globules are presented to the cells. But a mere me- 
 chanical mixture of oil and water, however finely sub- 
 divided for the moment, does not enable the oil to permeate 
 the delicate membranous walls of the cells. The experi- 
 ments proving this have an importance which demands 
 a more detailed description than my present space 
 permits, but I hope shortly to further particularize. 
 
 After fasting a dog for two days, a meal of beef kidney 
 fat was given, in which were a few pieces of old tanned 
 leather to excite due peristalsis. The bile and pancreatic 
 ducts were previously tied, and a ligature was passed 
 round the bowel, about two feet from the pylorus. At 
 the end of three hours the animal was killed, and the 
 condition of the intestine was examined, both microscopic- 
 ally and chemically, for any fat it might have absorbed. 
 Scarcely any oil globules were found to have entered the 
 cells of the villi with which the fat had been so long in 
 contact, and by exhaustion in boiling ether no difference 
 could be perceived in the amount of fat extracted from 
 the portion above the ligature, as compared with that 
 obtained from an equal weight of intestine taken from 
 below the part closed by tying. 
 
 A similar experiment was performed upon the intestine 
 of another dog, the only difference being that an alkaline 
 solution of pancreatin with bile extractive was mixed 
 with the fat before it was swallowed. A third dog was 
 fed as in the first case, but the natural secretions of bile 
 
FAT IN THE HUMAN BODY. 37 
 
 and pancreatic fluid were permitted to flow into the in- 
 testine. In both these latter cases the fat, in an oily- 
 state, was found in the cells of the villi, and analysis gave 
 evidence of a very large absorption of fat in the parts 
 above the ligatures, while in those portions beneath it 
 no increase of fatty constituents was yielded. 
 
 These results are in themselves sufficiently conclusive, 
 but I have observed that they are corroborated by all I 
 have ascertained concerning the still more interesting 
 processes by which fats pass through the various mem- 
 branes and tissues, when suitably prepared either by 
 natural or artificial means. It is at the very point of 
 transmittance that the complex actions and reactions 
 occur which are included in the but little understood 
 digestional absorption of fat. 
 
 The moistened membranes of the villi, lacteals, and 
 blood vessels do not pass free fixed oil by endosmosis, as 
 is believed by some ; neither will mere alkalinity assist in 
 its absorption, as I was able to demonstrate by a fourth 
 experiment. The mixture of pure pancreatic fluid and 
 fat appears almost equally incapable of being taken up 
 by the absorbents, but the experiments to determine this 
 were not quite so conclusive, probably because we were 
 unable to prevent the presence of fluids from the intes- 
 tinal glands. Many and various supplementary ex- 
 aminations confirm these data, and the necessity is 
 plainly shown for the presence of an alkali, pancreatic 
 fluid possessing full fermentative vitality, and certain 
 elements of the bile, to render fat truly soluble in the 
 fluid before it can be absorbed. 
 
 A very minute portion of the soluble oil appears 
 sufficient to effect the transfusion of a large quantity of 
 a fine emulsion. It may act by rapid endosmosis, carrying 
 
38 THE DIGESTION AND ASSIMILATION OF 
 
 with it the fixed fats, and may then return by exostosis, 
 having deposited the globules of free oil within the mem- 
 branes of the cells. By a similar action the fixed fats 
 may pass from one membrane to another, until it is mixed 
 with the ehyle in the lacteals and the blood in the 
 capillaries of the bowel. I am not in a position to 
 demonstrate that this is the precise manner in which the 
 soluble portion of the oil enables the other portion to be 
 absorbed, but I have proved that fat which contains no 
 soluble glycerides is not absorbed until the reactions of 
 the bile and pancreatic fluid have rendered a portion of 
 it soluble in water. 
 
 Whatever description of fat may have been eaten, it 
 must be so far transformed as to approach in composition 
 to that of butter or the fat of milk which has passed 
 through the mammary glands. 
 
 It may not be generally known that butter is, to a 
 certain extent, easily rendered soluble in water ; but as 
 this peculiarity affords the distinctive difference between 
 pure butter and the common fats with which it may be 
 adulterated, and as this is now relied on in butter 
 analysis for the detection of such adulteration, I may, 
 perhaps, be excused if I repeat the evidence of this 
 instructive fact, which first dawned upon me some three 
 years back. 
 
 Ordinary mutton, beef, and pork fats are composed 
 almost exclusively of the glycerides of the fixed fatty 
 acids, such as the stearic, palmitic, and oleic acids. If these 
 are saponified with hydrates of the alkalies, and the soap is 
 decomposed with a dilute acid, such fats will yield more 
 than 95 per cent, of the fixed fatty acids, which will float 
 upon the water, being absolutely insoluble in that con- 
 dition. If, however, butter is saponified, nearly 14 per 
 
FJCF IN TH^ HUMAN BODY. 39 
 
 cent, of other fatty acids and glycerin are sei free ; these 
 are both volatile and truly soluble in pure water. 
 
 The analogy is perfect between butter and the fatty 
 matters of food, after they have been acted on by the bile, 
 pancreatic, and other essential fluids in the intestine; a 
 portion of the fat, varying from 4 to 7 per cent., being in 
 true solution by the time its digestion is complete and 
 it is ready for absorption. A slight saponification is evi- 
 dently required to form a hydrate of the fatty matters 
 by the fixation of a portion of water. This product is in 
 its turn decomposed, and the soluble fatty acids and 
 glycerine liberated to enter into solution. Bernard has 
 always maintained that soap is formed in the intestine, 
 and I am sure that no careful experimenter can fail to 
 find it during a vigorous digestion of fat ; but I diverge 
 from M. Bernard's views when he assumes soap, as such, 
 to be the vehicle — much more, as the only vehicle — for 
 the transfusion of fats through the various membranes. 
 
 As I before stated, I am not greatly concerned now to 
 adopt any dogmatic theory of the exact minutiae of such 
 transfusion, but I must emphatically declare that I can 
 find no actual soap except in the intestine, even when a 
 considerable quantity of soap has been injected into it. 
 I therefore lean strongly to the opinion that saponifica- 
 tion is only a preliminary process, confined to the bowel 
 alone. The soap, when formed, has to be split up before 
 its are absorbed through the several membranes so 
 that they may be taken up in the circulation. 
 
 The very support afforded by this possible advance 
 upon previous tenets enhances the practical value of the 
 discovery that soluble fatty matters are ossontial to the 
 healthy secretion of the pancreatic glands. The experi- 
 ments which prove that the active functions of the pan- 
 
40 THE DIGESTION ANp ASSIMILATION" OF 
 
 creas depend chiefly, if not entirely, on its being itself 
 supplied with fat soluble in water, seem incidentally to 
 point out the conditions under which the supply can be 
 afforded. Having taken the subject thus far in recording 
 a brief generalization of my rough analytical notes, I 
 must reserve a few words explanatory of the attempts 
 made to arrive at a synthetical product complying to 
 some extent with these essential conditions. 
 
 CHAPTER IT. 
 
 ARTIFICIAL AIDS TO THE DIGESTION OP FATS. 
 
 All animals suffering from emaciation labour under the 
 same degeneration of the fat-digesting organs in varying 
 degrees. From whatever original causes the pancreatic 
 functions have lapsed into abeyance, no sufficient or 
 healthy flow of the digestional fluids is ever found during 
 wasting diseases. This is provably true of dogs, pigs, 
 calves, and other animals which become attenuated when 
 plentiful food is provided. It is not difficult to insert a 
 drainage tube into the pancreatic duct and test the differ- 
 ence of the emulsifying power of the fluids obtained on oil, 
 which may be compared with that produced by animals 
 possessing an obviously healthy digestion. A regular and 
 reliable flow of bile is equally essential to the formation 
 of soluble fat or oil, and this is as frequently found want- 
 ing during the digestion of food by all animals losing 
 weight, unless it be from over-exercise or want of proper 
 food. 
 
FAT IN THE HUMAN BODY. 41 
 
 Nothing appears to restore the healthy functions of 
 the liver and pancreas in these cases, except the frequent 
 ingestion of oil or liquid fat, so treated artificially that it 
 is already partially transformed by fermentation and the 
 reaction of bile. Seized on with avidity by the absorb- 
 ents, it is insensibly assimilated by the digestive organs, 
 until they gradually become strengthened, not only to 
 provide their own nourishment, but to transform a suffi- 
 cient quantity of fat to supply the inevitable waste 
 throughout the body. 
 
 The fat or oil most suitable for general nourishment is 
 evidently that which most nearly approaches the com- 
 position of the fat to be renewed, but a fallacy underlies 
 the proposal that the small quantity necessaiy to give a 
 periodic impetus to the digestion of the common fats of 
 food need be, or indeed ought to be, of this exact com- 
 position. 
 
 It is admitted by those who contend for the adminis- 
 tration of the more solid fats as a pancreatic emulsion 
 that, in the first instance, oil, such as cod-liver oil, " can 
 be hurried most rapidly into the jpulmonanj (?) circula- 
 tion ; it is the fluid oleinous kind of fat that can pass by 
 the portal instead of by the lacteal route." It is, as Dr. 
 Dobell says in another place, " like water to the uprooted 
 flower." But, then, this candid writer proceeds to advise 
 the use of solid pancreatized fat, because " if you keep it 
 (the flower) in water after it has revived, instead of 
 planting it in good soil, it will droop again and die for 
 want of materials on which to live." There would be 
 great weight in this, if the fat proposed to be made into 
 the emulsion ie exactly of the composition of human fat, 
 and no other fat slvould be taken in the ordinary diet. 
 Dr. Dobell, however, advocates the use of a far more solid 
 
42 THE DIGESTION AND ASSIMILATION OP 
 
 fat than human fat, and forgets that the animal fats of 
 food contained in his own dietary are also of this precise 
 nature. He also loses sight of the obvious necessity for 
 a due admixture of the "fluid oleinous kind of fat," to 
 approximate the harder fats of the diet to the normal 
 fatty matters of the human body. To continue his own 
 metaphor, the flower requires not only " good soil," but 
 periodic watering. 
 
 The advantage of an emulsion of the more fluid oil to 
 temper down the too great solidity of the other fats taken 
 in ordinary diet is therefore manifest. As I have proved 
 this to be the case with pigs, in which the lard more 
 nearly approaches the consistence of human fat, I think 
 we may assume the same to h;ld good in the human 
 digestion of fat. 
 
 Taking perfectly soluble pancreatin,* and completely 
 emulsifying a suitable oil with water (two parts to one), 
 I find there is a difficulty in preserving the ferment 
 principle from working itself out in the course of a few 
 days; after which the pancreatized oil will not com- 
 municate its emulsifying property to other fats or oils 
 with which it may be brought in contact, as it does when 
 the ferment is still in vigorous activity. Hence, we 
 should require a fresh preparation to be made almost 
 every day in summer-time, or the fatty matters of food 
 will not be transformed so as to be digested except by 
 those who do not require such assistance. To obviate 
 this, I made numberless experiments with temporary 
 antiseptics, and I conclude that one only is really suitable. 
 Boric acid appears to arrest any after fermentation in the 
 
 * If any portion of the pancreatin is insoluble in water, it denotes a 
 highly objectionable mode of preparation ; the true ferment being killed, 
 and the whole exceptionally liable to ammoniacal decompositior 
 
FAT IN THE HUMAN BODY. 43 
 
 emulsion without injury to it ; and when it is combined 
 with the soda to represent that constituent of the bile 
 always forthcoming in the naturally healthy digestion of 
 fat or oil, I observe that the salt formed becomes so 
 dissolved and diluted in the digestion of food that the 
 pancreatic ferment resumes its activity, and all the 
 other tats of the meal become in a like manner trans- 
 formed. 
 
 At this period of liberating the ferment from the 
 temporary antiseptic influence of the boric acid, there is 
 a liability to a slight putrefactive decomposition, which is 
 only restrained naturally by other principles of the bile. 
 At first I was led to attempt this artificially, by adding 
 glyco-cholic acid in its original combined state (the 
 "crystallized bile" of Plattner), but the flavor was so 
 nauseous that I could not get animals to swallow oil 
 prepared with it. Reflecting that the pancreatin used 
 was from the pig, and, according to Strecker, the bile of 
 that animal contains glyco-cholates differing from ox 
 bile, I refined the glyco-hyocholic acid until the objection- 
 able bitterness was removed, and I was pleased to 
 observe that its function in the intestines was but little 
 impaired. 
 
 Testing oil prepared with soluble pancreatin, soda, 
 boric acid, together with a trace of hyocholic acid, I have 
 every reason to believe that a transformable modification 
 of the oil is reached, which is digestible in the most 
 atrophied condition of the organs. 
 
 All the elements for a gentle but rapid saponification 
 are insured, and the splitting up of the soap is favoured 
 by the presence of a small quantity of already hvdrated 
 oil in Bolution. How little of this actually soluble 
 glyceride of volatile fatty acids is sufficient to continue 
 
44 THE DIGESTION AND ASSIMILATION OF 
 
 the hydration of the remaining fats during digestion is 
 almost impossible of estimation. I have, however, satis- 
 fied myself that very small proportions yield good results, 
 but slowly ; a larger quantity promoting extreme rapidity 
 of absorption. 
 
 Nearly two years of almost incessant observation 
 affords a fair means of judging as to the corroboration 
 since given by constant repetition of the more important 
 determinations. But the familiarity with the indications 
 thus acquired may inspire more confidence in the results 
 than might be accorded to the analogy between experi- 
 ments upon the lower animals and the effects of the 
 same kind produced in the human body. As soon, how- 
 ever, as the principle involved was made plain, every 
 opportunity was embraced of watching the direct work- 
 ing out of the problem, as applied to the assistance it 
 affords to the digestion of fat in the wasting diseases 
 which afflict humanity. 
 
 This more properly belongs to the science of medicine 
 than to that of pure physiological chemistry. I was, 
 therefore, fortunate in obtaining the assistance of Dr. 
 Drewry in elaborating the use of fatty matters con- 
 taining hydrated and soluble oil in cases of consump- 
 tion and other forms of wasting in the tissues. His 
 testimony as to its adaptability must speak for itself; 
 but some of his cases have been within my own frequent 
 observance, and I cannot refrain from expressing the 
 intense gratification it has afforded me to note the almost 
 immediate gain in weight and improvement of health 
 which has resulted, even in some of the worst instances. 
 
FAT EN THE HUMAN BODY. 45 
 
 ADDENDUM. 
 
 EARXT EVIDENCE OF THE COMMENCEMENT OF WASTING DISEASES 
 DISCOVERED BY THE EXCRETION OF SOLUBLE FAT. 
 
 Urese and fcecal excreta have been frequently sub- 
 mitted to me for examination by members of the medical 
 profession, in cases where there was reason to believe 
 a direct loss of fatty substance occurred through the 
 kidneys or bowels. 
 
 In certain morbid conditions I have found free fat 
 or oil in the urine. It was not detected in most cases 
 until after cooling, when it assumed a chylous or milky 
 appearance. This usually happened without the presence 
 of any considerable quantity of albumin. In other cases 
 fat or oil was found which never showed itself to the eye, 
 and these were invariably connected with phthisis, tabes, 
 or nervous wasting. The quantitative estimation of 
 these transparent fats always presented difficulties I 
 could not account for. In drying the residues I 
 experienced a loss of weight which continued as long 
 as they remained in the drying chamber of the water 
 bath ; repeated weighing could not, therefore, be de- 
 pended on to confirm the absence of the solvents. Since 
 making the discovery of the soluble and volatile fatty 
 matters produced by fermentation in the intestine, this 
 r, pancy is explained ; and I have no doubt, from 
 samples more recently analyzed, that mere traces of 
 soluble fat in the urine may frequently mark the earlier 
 stages of many wasting diseases. To obtain a certain 
 verification of this slight excretion, vapor distillation 
 must be resorted to, and the most accurate manipulation 
 
46 THE DIGESTION AND ASSIMILATION OF FAT. 
 
 is required to prevent the loss of such traces of soluble 
 volatile fatty matters as are sometimes to be found at the 
 commencement of the disease. 
 
 Similarly, I now always submit the foecal matters to 
 this, among other delicate tests. The result is that a 
 false or secondary digestion of fat is often found to have 
 taken place in the lower bowel without any benefit being 
 derived from it. On the contrary, it seems to denote one 
 of the first symptoms of the degeneration of the natural 
 fat-digesting organs. As this is of importance in point- 
 ing out a possibly unsuspected mischief, I have thought 
 attention should be directed to the means analysis affords 
 of confirming or removing uncertain suspicions as to such 
 morbid conditions. These may, or may not, be intimated 
 by a slight glistening film, either on the surface of the 
 solid excreta or floating in the urine. 
 
 Interesting as such investigations are in supplementing 
 the foregoing inquiries, I have had to regret the interrup- 
 tion lately of experiments extending over nearly seven 
 years. The unexpected enforcement of certain rules of 
 Gray's Inn has practically closed my laboratory there 
 for these purposes. I have, however, now made special 
 arrangements at my new laboratories in Duke Street, 
 Grosvenor Square, which will, I hope, enable me to 
 complete at least some of the other physiological experi- 
 ments, and to proceed with analyses such as have been 
 lately forbidden to me. 
 
 96, Queen Anne Street, 
 
 Cavendish Square. 
 

 Date Due 
 
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 JUL 1 
 
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 Digestion and assimilation of fat 
 
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