0&,S mP'W #p/,; v-.;. Mii^ iPIPfi i#''^p^§p ,d'- ^ssia ipPft". / Wi® £dpp ■'-\'W-:/ r'«i UNITED STATES OF AMERICA WASHINGTON, D. C. GPO 16—67244-1 AN ATTEMPT^ TO PROVE THAT":;^V^^^ DIGESTION, IN MAN, DEPENDS ON THE UNITED CAUSES O F SOLUTION AND FERMENTATION. —&>*•£§— By JOSEPH GLOVER, Of Charleston, South-Carolina., MEMBER OF THE PHILADELPHIA MEDICAL AND CHEMICAL SOCIETIES, Tentanda via eft, qua me quoq ; polfim /_ C^: w 'J< ' l^llere humo.--------------—— Vir i«. ■» PHILADELPHIA: ^.' { j,^"^™ PRINTED BY WAY & O R O F F'; No. 48, North Third-ftreet. 1800. AN INAUGURAL EXPERIMENTAL INQUIRY, FOR THE DEGREE 07 DOCTOR OF MEDICINE; SUBMITTED TO THE EXAMINATION OF THE REV. JOHN EWING, S. T. P. PROVOST; THE TRUSTEES & MEDICAL FACULTT, OF THE UNIVERSITY OF PENNSYLVANIA, On the thirty-firfl. of May 1800. 399©ai TO DOCTOR MATTHEW IRVINE, FHYSIClAN OF CHARLESTON, SOUTH-CAROLINA, WHO, IN THE TWO-FOLD CHARACTER O F A FRIEND and PRECEPTOR, HAS THUS FAR GUIDED ME, BY HIS PATRONAGE and CARE, THROUGH AN IMPORTANT BRANCH OF SCIENCE} THIS PUBLICATION IS RESPECTFULLY INSCRIBED, AS A SMALL TESTIMONY OF ESTEEM AND GRATITUDE, BY HIS MUCH OBLIGED FRIEND AND PUPIL, J. GLOVER. , TO BENJAMIN SMITH BARTON, M. D. PROFESSOR OF MATERIA MEUICA, NATURAL HISTORY AND BOTANY, IN THE UNIVERSITY OF PENNSYLVANIA, THIS DISSERTATION IS LIKEWISE INSCRIBED, AS AN ACKNOWLEDGMENT OF THE ATTENTION AND ADVICE WITH WHICH HE HAS HONOURED HIS MUCH OBLIGED FRIEND, J. GLOVER, PREFACE. JL HE difficulty of experimenting, appears to be the reafon, why phyfiology has not kept pace with other branches of medical fcience. In mod of thefe we may travel on a fmooth and delightful road; but the mod trivial circumftances influence the refult of experiments; thus aflertion is oppofed to aflertion, and on the reputation of the author refts the pofition. In the following pages it is contemplated to in- veftigate the procefs of digeftion ; a fubjecr, by no means perfectly underftood. In doing this, I have endeavoured to arrange fuch ideas on the fubjecl:, as I have collected from the opinions of others, or from fuch fads and experiments as I have myfelf afcertained. Thefe have taught me the difficulty of explaining the phenomena of digeftion on molt of the theories which have been advanced; nor do I expect that the one, which I have adopted, is void of imperfections. Too fond of reducing every ope- ration of the animal ceconomy to a fmgle principle, many phyfiologifts have explained the procefs of digeftion on fome favourite theory, and thus, by fetting a limit to the hand of nature, have left un- accounted for fome of the moft important pheno- IO The refult of my inveftigations, fuch as it is, circumftances have induced me to caft as my por- tion into the fcale of fcience. Should it fuggeft an idea worthy the attention of the philofopher, I fhall feel highly gratified; but, on the contrary, fhould my experiments prove inconclufive, and error ftamp the reputation of my eflay, ftill I fhall be pleafed with the reflection, that the moft feeble at- tempt to elucidate this important branch of phyfio- logy, can be by no means injurious to fcience. The hafte, fo unavoidably annexed to the fhort time allotted for this publication, will no doubt in- duce the reader to overlook the many inaccuracies of language, which I am fully aware are contained in the following pages. They may perhaps bring to his recollection, that fentence of Dr. Beddoes fo expreffive of the liberality of the philofopher, when he fays, " we fhould fet a due value on our " prefent knowledge, though it be imperfect; and " reftrain thofe rude hands, that are ever ready to " pluck up the tender plants of fcience, becaufe " they do not bear ripe fruit at a feafon when they " can be only putting forth their bloffoms." Im- prefled with the generofity of thefe ideas, I fubmit my obfervations and experiments to the candid in- veftigation of the philofopher, whofe patronage alone ftamps the merit of every youthful perform- ance, gives activity to the mind, and fanctions fu- ture inveftigations. o AN AN INAUGURAL EXPERIMENTAL INQUIRY, &c. —§*>*«§— SECTION I. Obfervations on Digeftion. -LVX AN, like every other being in nature, requires a continual and regular fupply of food, for the fe- veral purpofes of fupporting life, of promoting the growth of his fyftem until he arrives at maturity, and of forming new parts when fuch become neceflary. Indeed, on contemplating the complicated ftructure of his frame, it is evident, that a continual lofs of thefolid and fluid parts, of which he is compofed, mult be the inevitable effect of every action or func- tion of life which he performs. Nature, always wife, to obviate this general wafte of his fyftem and continual tendency to decay, made it neceflary that he fhould have fome inducements. to repair it, and thus be reminded of the connec- tion which exifts between aliment and life. Ac- cordingly we find he is indued with the ftimulus of hunger and third, which, together with the plea- fure !2 Aire he receives from gratifying thofe appetites, in- duce him to take into his ftomach a certain quanti- ty of matter to allay thofe difagreeable fenfations. This matter includes, not only the feveral kinds of animal and vegetable fubftances which we denomi- nate food, but alfo comprehends the fluids taken in with which they are diluted. Thefe having arrived at the ftomach which is the great receptacle of his aliment, a greater or lefs length of time is requifite, according to circumftan- ces, for them to undergo thofe procefles which are eflential to their aflimilation being completed. In fact, I conceive it an impoflibility to determine with any certainty, the exact time neceflary for the di- geftive organs to perform their refpedtive functions* as that will depend in a great meafure on the ftrength of thofe organs, on the quality, quantity and manner in which the food is prepared, its pre-, vious mafticatjon, and various other caufes of which we are not always aware. The moft prevalent opinion on this fubject, is, that from about the third to the fixth hour after food is taken, it is difcharged, through the pylorus, of a pultaceous confidence. There are however fome extraordi- nary deviations from this allotted time, which cannot but convince us of the great uncertainty of calculations of this nature. We have on record inftances related of fubftances remaining in the ftomach indigefted for months j and on the contrary, «J contrary, that in two hours after food was taken into the ftomach, that organ was found empty.* Thefe I conceive to be rare occurrences, neither do I believe it by any means common, even in the fpace of three hours, for the ftomach to difcharge its contents; as in a majority of mankind, I pre- fume, a much longer time is requifite for food to undergo thofe changes, which are ufually effected on it during its flay in that organ. To our feveral kinds of aliment, different con- diments are added by various nations, many of which merely gratify the palate, while others aflift in promoting digeftion. Among us at, prefent fea fait is moft univerfally ufed for this purpofe.f Pro- feflfor Chaptal tells us, that the acidulous tartrite of pot-afh is greatly confumed in the north of Europe, where it is ufed as a table feafoner ; and Profeflbr Barton has informed me, that the Creek Indians make ufe of hiccory afhes, and that in fome of the fouthern ftates, the afhes of a particular kind of marfh-grafs were formerly preferred for the fame purpofe. Befides this difference in nations with refpect to condiment, there is one of ftill more confequence, which is, their ftriking peculiarities in the choice of food. We find, that in Lapland, Iceland, Greenland, * Vid. Haller's Element. ,). Phyfiol. Tom. VI. page 381. f According to the experiments of the celebrated Pringle, a fmall quantity of fca fait iiaftcns putrefaction, while a larger quantity rctardi thatprcceft. Difeafa of the army, ApemHx, paper 3. Expcr. 2j. 14 Greenland, Norway, and other cold countries, the" inhabitants live chiefly on fifh andflefh;* while, on the contrary, we are informed of certain fects in India, who live almoft, if not folely, on a vege- table diet. Both the Laplander and the Indian enjoy their health in thefe extremes ; their habits, together with their climates, being better adapted to their refpective modes of living; as the fouth- ern latitude, in which the latter refides, appears to prevent his fubfifting for any length of time, on fifh or flefh ; while its flimulus is abfolutely ne- ceflary to fupport the general wafte of the fyftem, to which the former is expofed from cold. A ma- jority of mankind live in the medium of thefe ex- tremes ; experience having taught them, that a due proportion of animal and vegetable food, is the better adapted for their nourifhment, the one coun- teracting the ill effects arifing from the other. Of all animals man appears to be the moft om- nivorous. Deftined to range through every the moft diftant part of our globe, he is capable of accommodating himfelf to the food of every coun- try. Certain other animals are likewife capable not only of changing their accuftomed diet, but fometimes * This is fometimes (though more rarely) the cafe in fouthern lati- tudes. At Orange river, in Africa, Fordyce tells us, that the inhabit- ants live upon limpets, dead and putrid feals and whales, not tafting a particle of vegetable food of any kind, excepting aromatics. Treatift on Food. p. 175, l5 fometimes acquire fo vitiated a tafte, as to refufe their former food. This was particularly the cafe with the wood pigeon of Spallanzani. This acute phyfiologift tells us, that by dint of hunger he brought this bird to relifh flefh fo well, that it re- fufed every other kind of fuftenance, even grain, of which it is naturally fo greedy. Various other fads of a fimilar nature, are found on record. Von Troil informs us, that the Icelanders, when there is a fcarcity of fodder, feed their cattle with fteenbitr, (a kind of fifh) which, together with the heads and bones of cod, is beaten fmall, and mix- ed with one quarter of chopped hay. He further adds, that the cattle are fond of this food, and yield a good deal of milk after having ufed it.* Profefior Barton, in his courfe on natural hifto- ry, has likewife related a faft no lefs interefting. He has told us, that deer have been frequently obferved to feed on dead fifh, which had been wafhed up on the banks of the Sufquehannah and other rivers. Thefe are inftances fufficient for my purpofe, but many others of equal importance might be collected. From the feveral kinds of aliment taken into the ftomach, man is plentifully fupplied with fluids, and from the component parts of thefe fluids, iv the growth of his fyftem and the folids of his body produced. This growth of his fyftem and pro- dudion of folids is induced, although he may fub- fift * Vid. LeUers on Iceland, p. IJ.V i6 fill on very different kinds of food, as by the pecu- liar operation of his digeftive organs, he is capable of aflimilating, by certain proceffes, matters taken from either the animal or vegetable kingdoms into a fluid fui generis. Thefe proceffes of aflimilation are comprehended in the term digeftion ; by it we are to underftand, thofe proceffes which take place in the digeftive organs of man, and by which his ' food is converted into laudable chyle. The modus operandi of nature in this converfion of our food into chyle, has attracted the attention of philofophers in every age, and various theories have been advanced to explain the phenomena which occur. With this view we find, that, the theories of the heat of the Jiomach, of mechanical aclion, of fermentation, of folution and others, have all been advocated by men, whofe fame has added reputation to their opinions. But, as no one of thefe can exclusively account for all the phenome- na of digeftion, and as in the choice of a theory, the preference fhould always be given to fuch a one, as will explain to us the moft of them; I am induced to adopt another, and attempt to prove the dependency of this important function, on the united caufes of folution and fermentation. Of the Heat of the Stomach. The theory, of the heat of the ftomach, ,was at one time fo fafhionable, that Profeffor Blumen- bacri «7 back tells us, inftead of the term digeftion, that of ccction, was formerly ufed by the greater part of phyfiologifts.* This opinion, however, I believe at prefent has but few advocates, as I prefume no perfon will now contend that heat is the fole caufe of digeftion. This would be equally as incorrect to fay, that it does not affift in promoting that pro- cefs. While we refufe to admit, that heat is the fole efficient caufe of digeftion, we cannot but acknowledge its effect in expediting that procefs, as it has been long fince made evident by experiment. It therefore only remains that we fhould fhew from the fituation of the ftomach, that it is advantageoufly feated to be fupplied with heat from its neighbour- ing parts, as we may eafily conceive from contem- plating their relative fituations with refpect to it. We find that its right fide is covered by the thin edge of the liver ; its left touches the fpleen ; that behind it is the feat of the pancreas, and immedi- ately above it is the diaphragm ; that the peritoneum lies before it, which, by the action of the abdomi- nal mufcles, gives it a motion diametrically oppofite to that which it receives from the diaphragm in re- fpiration ; and that the aorta, the largeft artery in the body, lies juft behind it. All of thefe circum- ftances muft tend to give it additional heat. Hence we may with propriety acknowledge the accuracy of Dr. Barry, when he tells us, that " the heat of " the » Inftitut. PhyGol. Vol. II. p. 2J. c i8 " the ftomach in a healthy man, is greater than'the " common heat of fun in a fummer's day."* Of Mechanical Aclion. To difprove that the mechanical action of the ftomach has any effect in promoting digeftion, I need fay but little. Facts fpeak for themfelves. That accurate experimenter, the Abbe Spallanzani, has decidedly proven the very wonderful mufcular action exerted in the ftomachs of fome animals; but his experiments likewife tend to fhew, that no fuch action takes place in the human ftomach, Having frequently fwallowed wooden tubes during his experiments, which were made fo thin as to be incapable of bearing the flighteft preffure; he ne- ver, in a fingle inftance, difcovered one of them to be broken. In addition to this, he mentions the fact of cherries and grapes being voided entire, as I have myfelf frequently obferved. He likewife relates an experiment with ripe grapes, which we all know to be incapable of bearing the leaft me- chanical action, which appears to be directly in point. " Of twenty-five," fays he, " which I " fwallowed, eighteen were voided entire, of the " other feven, the {kins only appeared."! Thefe experiments alone, I deem fufficient to prove, that no triturating power is poffeffed by the human fto- mach, * Yid. Treat, on Digeft. p. 8. | Natural Hiftory, Vol. I. p. aia. *9 mach, particularly as the fact of grapes being voided entire, muft be notorious to every perfon who has attended to the fubject. In fhort, I do believe, that the mufcular fibres of the ftomach, have no other effect on our food, than merely that of propelling it through the pylorus. Of Fermentation. While fome phyfiologifts of confiderable reputa- tion, have confidered fermentation as quite fuffici- ent to explain all the various phenomena of digefti- on, others of equal celebrity have contended, that no fuch procefs takes place in a healthy ftomach. This diverfity of opinion, I cannot attribute to motives of prepoffeflion in favour of any particular theory, but would rather prefume, it was the confequence of a fuppofition, that to admit the one to be a fact, would be a tacit acknowledgment that the other could not be true. This too I fuppofe is the reafon, why even at the prefent time, thofe who have afcertain- ed the folvent power of the gaftric juice, will not admit that fermentation ever takes place in a healthy digeftion. But this, perhaps though too common an error, is ftill one by no means the lefs prominent. Does not chemiftry teach us, that nature frequently requires in her operations a multiplicity of caufes to induce a fingle effect ? Why then, if one of the caufes, which have been advanced, is not fufficient to explain the phenomena which occur, fhould we attempt 23 attempt the eftablifhment of another, equally ina- dequate to account for the wonderful effect of the converfion of our food into chyle ? The operations of nature are uniform, and fre- quently too deep for the fhallow limits of human wifdom to demonftrate; but I think, when we fhall have been more fuccefsful in our experiments, it will be found, that digeftion depends on the com- bination of feveral caufes, and that fermentation does certainly take place, as I fhall endeavour to prove in a fubfequent part of this effay. Of Solution. That folution does likewife take place in digeftion, I do believe, as the experiments of many phyfiolo- gifts of considerable reputation tend to prove the pofition, and my own have induced me to embrace it. The opinion, however, is by no means novel. Barry informs us, that " Bafil Valentine was the " firft among the chemifts who fuppofed that ani- " mal digeftion was owing to an acid diffolving " menstruum." That " Paracelfus received this " opinion from him." And that " Van Helmont " carried it farther; and afferted, that the fpleen " prepared this menftruum, which was from thence " conveyed into the ftomach, by the vafa brevia." Hence it appears, that the theory of folution has been long fince favoured. Since when, very ac- curate experimenters have written, in hopes com- pletely 11 pletely to decide the queftion in its favour. But, although they have moft demonstratively proven the folvent power of the gaftric juice, they have by no means fhewn that fermentation does not likewife take place. For my own part, I do not hefitate in believing, that both folution and fermentation do take place in a healthy digeftion; indeed I think, with correctnefs I may venture to affert, that in the human ftomach, fermentation does as neceffarily follow folution in the converfion of food into chyle, as thought fucceeds impreflion in the formation of ideas. Food, in the firft inftance, is considerably attenu- ated, by the maftication which the rotatory motion of our jaws and preffure between our molares are fo capable of giving it. Its particles being thus di- vided, are intimately mixed with the mucus of the mouth and faliva, after which it paffes down into the ftomach. This we may term a procefs prepara- tory to digeftion. It is certainly* one of much more confequence to the perfect digeftion of our aliment, than is generally fuppofed; as it is evident thofe perfons, who half chew or bolt their victuals, as it is called, are generally subject to all the numer- ous difeafes arising from indigeftion. Hence ap- pears the neceflity of perfons being particular in the maftication of their food, as nothing fcarcely can be of more injury to the constitution, than continually to fupply the ftomach with indigefiible half-mafticated food. Something, 24 Something, in its effect very similar to maftica- tion, is obfervable in domestic fowls. They, by a peculiar instinct, take into their gizzards, pebbles and gravel, which certainly ferves in them every purpofe, which teeth do in fome other animals. I have made ufe of the word instinct through choice, becaufe I cannot believe with Spallanzani, that they are picked up by mere accident, or through their ignorance in mistaking them for food. One fact appears to oppofe his theory, which is, that thofe fowls which are kept on a gravelly foil are rarely if ever found to have a greater number of ftones in their gizzards, than thofe raifed where lefs gravel is prefent. Again, if they were picked up by acci- dent, we fhould expect that they are not at all neceffary to their health ; whereas, the very reverfe of this is the fact. A very refpectable author, who investigated this subject with considerable fuccefs, by experimenting on chickens hatched with artifi- cial heat, has given us the very belt information I have perufed. He fays, " I have hatched vast " numbers, and frequently have given the chickens " fmall feeds whole, taking care that they fhould " have no ftones. In this cafe the feed was hardly " digested, and many of the chickens died. With " the fame treatment in every refpect, others who " had their feeds ground, or have been allowed to " pick up ftones, have none of them been loft."* This would appear to fhew, that pebbles are eflen- * Fordyce on Food, p. 34. ' 23 tially requifite to the healthy digeftion of thefe ani- mals. Indeed, the experience of many perfons tends to prove this to be the cafe, as we often hear of their fending for gravel for their poultry, and when interrogated why they do this, they tell us, that without it their fowls grow poor, dwindle away, and fometimes die. Mr. John Hunter, com- menting on this affertion of Spallanzani, that peb- bles are picked up by birds through chance or ignorance, fays with much humour that" it appears " fingular, that only thofe which have gizzards " fhould be fo ftupid." The more freely food is masticated, and the more minutely it is divided ; the lefs heavy does it lay on the ftomach, and the more eafy it is of digeftion. The experiments of Spallanzani,* made on himfelf, prove the latter position; the former is obvious to common obfervation. Maftication not only pro- motes digeftion, by minutely dividing the matters to be carried into the ftomach; but likewife, by mixing them with faliva to form a pulpy mafs, it involves a very considerable portion of atmospheri- cal air, which, being rarefied by the heat of that organ, tends considerably to burft the feveral par- ticles of food from each other. Here then we fee that it indirectly promotes folution, for, as the feve- ral particles of food are feparated from each other, in that proportion will folution be expedited; be- caufe, a greater number of furfaces will thereby be expoied * Natural Hiftory. Vol. S p 534- 24 expofed to the action of the gaftric juice, and of confequence the food will be the more fpeedily dif- folved. In the investigation of a subject like the prefent, it is neceffary that we attend particularly to the caufes which influence digeftion, and judge of their effects, by comparing them to the effects of similar caufes out of the body. And again, by accurately examining the products of digeftion, and by com- paring them to similar products out of the body, thereby investigate its caufes. Thus, as all vege- table fubftances, capable of undergoing the vinous fermentation, contain the conftituent principles of carbonic acid and of alcohol, and as thefe fubftances are obtained from fuch vegetables, the former dur- ing the fermentative procefs, and the latter after that procefs has ceafed; it is evident, if fuch pro- ducts are obtained from the digeftion of food in the ftomach, it must be the effect of a similar procefs.. The fame obfervations will apply to the other stages of fermentation. In the following pages, I fhall endeavour to relate in brief detail, fuch facts and experiments as have induced me to adopt the prefent theory. This will be done in three feveral fections. In the first I fhall proceed to deliver a few obfervations on the matters which influence digeftion. The fecond will con- tain an attempt to fhew, how far folution is admissi- ble in digeftion. And in the third and laft, I fhall endeavour to relate, why it is prefumable that fer- mentation does likewife take place. SECTION. 25 SECTION II. OF THE MATTERS WHICH INFLUENCE DIGESTION. THE chief of thefe are, faliva, the gastric juice, the mucus of the primae viae, the bile, and the pancreatic juice. And, lit. Of the Saliva. By faliva we mean that colourless, glutinous, and refolvent fluid, which is fecreted by the parotid, fubmaxillary, and fublingual glands. It is perfectly taftelefs and inodorous in health, and confifts of water holding a mucilage and certain falts in folution. On being placed on the firef its watery part fpee- dily evaporates, leaving its falts in a state of crystal- lization, refembling two or three different kinds of fait. Thefe are, according to Fordyce, fea-falt and fal-ammoniac, together with various other crystalli- zations of irregular forrhs; and agreeable to Plenck, fal-ammoniac and animal earth ; the former he in- ferred from triturating quicklime with faliva ; the latter from falival calculus and the products of fire. Saliva from its fapid nature, gives an increafed flavour to food. It tends to relieve thirft, by fup- plying the mouth and fauces with a iufficient quan- tity of moisture ; and has a certain and evident effect in digeftion. It does not however, poffefs a folvent D power i6 power, as has been afferted by fome, at leaft it does not poffefs this property in a greater degree than fimple water. I put an ounce of pure faliva, and as much of fimple water, into two feparate phials j to each of thefe I added two drachms, of roafted veal. Thefe phials were placed uncorked in a fand bath, which was kept as near as poflible to the heat of the hu- man body. After fuffering them to remain at reft for eight and forty hours, I decanted the water and faliva from each of the phials. The veal which had been immerfed in water, and that which had been in faliva, were now placed feparately on bibulous paper and as much of their moisture removed as poflible. The one which had been in water, was now weighed; it had loft twenty-three grains of its weight. On weighing the other, it had loft no more. This would certainly feem to fhew, that faliva has no folvent power, at leaft not out of the body. Again, it has been afferted, that faliva corrodes copper and iron more fpeedily than fimple water.* To afcertain this point, I made the following ex- periment : Having placed twelve grains of fheet copper in a phial containing faliva, and the fame quantity in another of equal fize, containing water only; I put them both in a fand bath, which was generally about the temperature of one hundred of Fahren- heit. * Vid. Haller's Element. Phyfiol. Tom. VI. p. 54. and Plcnck on Hum. Fluids, p, 7a. *7 heit. They were both kept in this situation for one week, at the expiration of which time, they were taken out, wiped dry, and "weighed. I could not difcover, that either one of them had loft more of its weight than the other. From this I presume we may conclude, that faliva has not a much greater effect, if any, in the corrofion of copper, than fimple water. Defirous of knowing what effect faliva has in digeftion, and with a view of afcertaining whether it poffeffed a fermentative property or not, I expofed equal portions of leavened bread and roasted veal, in two feparate flasks, to the heat of a fand bath, which I was careful to keep as near as poflible to the temperature of the human body,* or from nine- ty-fix to ninety-eight of Fahrenheit. To one of thefe flafks, I had previoufly added eight ounces of water; to the other, feven ounces of water and one of faliva. The veal, to which faliva was added, I took the precaution of mafticating, in order that it might be the more accurately blended with that fluid. In the fpace of fix hours, the one contain- ing faliva fmelled a little four, emitted air bubbles, and fhewed evident marks of fermentation. Where- as, that procefs did not commence in the other, which contained water alone, until four hours after. Profeffor Rufh has long fince made a fimilar and very decided experiment. " To elucidate the pro- " perties of faliva," fays our author, " I placed " mutton 28 " mutton and bread, of each two drachms, in two " glafs veffels. To one I added an ounce and a " half of faliva, to the other the fame quantity of " water, and placed both of them in a fand bath. " Five hours having elapfed, the -mixture with fa- " liva began to ferment. In feven hours, it dif- " covered evident marks of acidity; whilst, in " that, to which water was added, fcarcely any " motion was perceptible. After twelve hours had " elapfed, the mixture with faliva emitted a putrid " fmell; whilst the mixture with water remained " mild and inodorous to the twentieth hour."f An experiment fomewhat similar, has likewife been made by Pringle, but not with exactly the fame fuccefs. He expofed two drachms of frefh meat and the fame quantity of bread, together with wa- ter and faliva, to the heat of a furnace, kept at the temperature of i oo of Fahrenheit. The mix- ture remained about two days, he fays, with fcarce any vifible fermentation ; but on the third day that procefs became manifest.} This investigation, how- ever, does not appear to have been made fufficient- ly fair, for he tells us, that his experiment was made in a clofed phial. Now we know that the prefence of vital air, is a circumstance effential to fermentation, and hence its exclusion muft have been the caufe of that procefs being retarded. In every f Inaug. Differ, de Coct'o. Cib-in Vent. Exper. V. | Vid. Difeafes ef the Army, Appendix, paper 4, Exper. 30. every comparative experiment like this, every cir- cumstance fhould furely be made as fimilar as pofli- ble, to thofe which occur in the living ftomach, and of confequence there fhould be an admiflion of vital air, as this fluid is always involved in faliva, which is feveral times in the courfe of a fingle mi- nute conveyed into the ftomach. We are informed, that fome uncivilized nations, are fo well aware of the fermentative property of fa- liva, that they prepare an intoxicating drink, by mixing faliva with certain vegetable fubftances. Plenck relates, that they prepare it from the chewed roots of the jatropha manihot or caffada and piper methifiicum. Whether faliva poffeffes a feptic or antifeptic quality, has likewife been a fubjed of fome con- troversy. To fatisfy myfelf on this head, I placed equal quantities of roasted veal, in two feparate phials of the fame fize. To one, I added an ounce of pure faliva, to the other, as much of fimple water; thefe I placed, uncorked, in a fand bath, which I endeavoured to keep as near as poflible to ninety-fix of Fahrenheit. The heat of the bath, how- ever, was fometimes as high as one hundred and ten, but never below fifty. In twenty-two hours, the' one containing faliva emitted a putrid fmell; the other only fmelled four. In eighteen hours after I examined the phials again ; they both fmelled putrid; the one with faliva was the moft fo, 3° fo, and likewife had changed its colour a little, which was not the cafe with the other. From thefe experiments, I prefume it appears, that faliva poffeffes the property of promoting both fermentation and putrefaction; and not that it pro- motes fermentation, and at the fame time retards putrefaction, as has been fuppofed. The quantity of twelve ounces of faliva, is ge- nerally fuppofed to be fecreted by an healthy adult, in the fpace of twenty-four hours. At leaft this is according to the experiment of Nuck, whofe affertion I believe continues to be considered as the moft correct. The quantity however, is capable of being wonderfully increafed by certain medi- cines and other stimulants. Indeed Haller fpeaks of fifteen ounces being effufed in the fpace of thir- ty minutes.* 2d. Of the Gaflric Juice. The gaftric juice in health, is a colourlefs and turbid fluid, void of both tafte and fmell; and I must add, bearing considerable refemblance to fali- va. I do not believe, as fome authors have fup- pofed, that it is fecreted from the fmall glands of the ftomach, as it is inconceivable to me, how fuch minute glands could be the fource of fuch large quantities of this fluid, as are at times fe- creted. I therefore fhall prefer embracing the * Vid. Element. Phifiolog. Tom. VI. p. 59. •* I 3l theory of thofe, who fuppofe the immediate fource of the gaftric juice to be the extremities of the ar- teries of the ftomach; for I can as eafily conceive, in the wifdom of nature, that arteries may be ex- panded on the coats of the ftomach in fuch man- ner as to perform fecretions, as that they fhould be united together by &e cellular membrane, in the form of glands for the fame purpofe. Many perfons are at prefent of opinion, that the gaftric juice contains an acid. From the experi- ments of the Abbe Spallanzani, from thofe of his colleague Profeffor Scopoli, and indeed from thofe of many others, I think we have good reafon to doubt of the prefence of a fenfible acid in the gaftric juice. Having obtained fome pure gaftric juice from my own ftomach, I found it capable of coagulating milk very readily. This however I conceive as no proof of acidity being prefent, as I have coagulated ir with a folution of frefh runnet, in which I could not detect the fmalleft particle of acid. Nothing- can be more erroneous than the opinion which prevails among fome perfons, that acids alone have the power of curdling milk. The truth is the very reverfe of this; for it is now known, that the heart, lungs, and even liver of a turkey have been difcovered to poffefs this property.* It will furely not be faid that they are likewife acid. Again, certain vegetables, as the galium luteum, or * Vid. Spallanzani. N.it, Hift. Vol. I. p. 171. 32 ladies bed-straw, vaillantia cruciata or crofs wort, rubia tinctorum or madder, carduus or thiftle, cy- nara fcolymus or artichoke, as well as many others, have been obferved to have this effect. Indeed liv- ing fifh have been obferved to have this property; and Jacquin tells us,* that even lime-water produ- ces an imperfect coagulation of milk. Another fact, of no trivial import in the decifion of this question, is related by Mr. John Hunter. This gentleman tells us, that " in the flink calf, "near the full time, there is no acid found in "the ftomach; although the contents have the "fame coagulting powers with thofe of animals " who have fucked."f Now, as this coagulating property is evidently communicated to the ftomach by the gaftric juice, and as an acid could not be detected in the stomachs of thefe young animals, although they poffeffed this coagulating property, I think it appears fufficiently clear, that an acid does not exift naturally in the gaftric juice. This fact I confider as conclusive, at leaft in as far as it pre- vents our being deceived by acids which are evolved in digeftion. Haller likewife appears to have been fully per- suaded, that pure gaftric juice does not contain an acid, and has quoted the authority of at leaft a doz- en perfons to prove his affertion. J To determine this * Vid. Element. Chem. treat, de ladle. ■J- Vid. obfervations on the animal, ceconom. p. 163. \ Vid. Element, phyfiol. Tom. VI. p. 143. 33 this point however more fatisfactorily, as it is of fuch importance in the adoption of a theory of digeftion, I made the following experiment. Deeming it neceffary to obtain the gaftric juice perfectly free from any extraneous matter, and like- wife from any acidity of a former digeftion, I kept a cat fasting eight and forty hours, after which it was killed. I found no food in its ftomach, and but a fmall quantity of gaftric juice. This I fubmitted to the ufual tefts for detecting the prefence of an acid, but could not difcover any. Hence I have been induced to conclude, that the gaftric juice does not contain a fenfible acid, and that whenever an acid is prefent in that fluid, it raufl either be the ef- fect of difeafe or proceed from the remains of fome former food. Barry fays," that the humours which are contain- " ed in the stomachs of the moft rapacious birds, " fifhes, and beafts of prey, have never an acid, « but a faline tafte."* And from the chemical analyfis of the gaftric juice of the crow, by Profef- for Scopoli, we find he could not detect the prefence of an acid in that fluid, but difcovered it to be com- pofed of, firft, pure water; fecondiy, a fapona- ceous and gelatinous animal fubftanee ; thirdly, fal-ammoniac ; and fourthly, an earthy matter fimi- lar he fays, to that which exists in ail aniis.*; fluids. We * Treat, on Digeftion. p. 22. E 34 We come next to confider the folvent power of the gaftric juice, which is the great bafis on which the whole of the prefent favourite theory of digef- tion depends. Spallanzani tells us, that this fluid in a dog, not only acts on bone, but even corroded the denfe ena- mel of two dentes incifores taken from the up- per jaw of a fheep.* And from experimenting on himfelf, he found he could digest not only " muf- " cular fibres and membrane, but tendon, carti- " lage, and even bone itfelf, when not too hard." From the excellent inaugural thefts of Dr. Stevens, we likewife learn, that various animal and vegeta- ble fubftances, were diffolved by the gaftric juice of the human ftomach when inclofed in fpheres. In like manner bone, and even ivory fpheres were diffolved, which he had introduced into the fto- mach of a dog. Since the publications of thefe two ingenious gentlemen, and particularly fince the paper of Mr. John Hunter has appeared, further inveftigation of the folvent power of the gaftric juice feemed unne- ceffary. This gentleman difcovered, that in thofe perfons who had died of violent deaths, the ftomach itfelf was corroded and diffolved at its great extre- mity, and accounts for the ftomach not being acted upon during life, on the theory of a living princi- ple. Several facts tend to fhew, that there is fome- thing innate in living matter, which resists tjhe ac- tion ' Vid. Natural Hiftory, page 21X. 35 tion of the gaftric fluid. It is well known, for in- ftance, that worms exift in the human ftomach unaf- fected by digeftion while living, but are fpeedily acted upon by the gaftric juice as foon as they are deprived of life. To account for this fact, we muft confider the gaftric juice as a mere chemical folvent; then, by reflecting that all chemical folvents act by attraction, we may fay, that the action of the veflels in living- matter, is too great to be overcome by the attrac- tive force of the gaftric juice, and confequently their combination cannot take place. Another fact which fhews, that the folvent power of the gaftric juice is decidedly inert, as it refpects fome kinds of living matter, is, that there are feveral fpecies of ferpents, and particularly the rattle fnake, who receive their young on the leaft alarm, down their throats into their stomachs, where they have been known to re- main for three and four hours. Fifteen or twenty of thefe young rattle fnakes, have been found in the ftomach of an old one, and not in the leaft in- jured by the gaftric juice.* " A polype" too " in- " ferted into the ftomach of another polype, con- " tinues to live as before."! Although convinced from thefe facts, of the inert- ness of the gaftric juice on thefe animab, ftill I was not fatisfied of its action on other living animals. I therefore determined on an experiment with the gaftric juice of a dog. For this purpofe I kept a dog "Profcffor Barton's Lectures on Natural Hiftory. f Spallanzani's Natural Hiftory, Vol. I. p. III. 3* dog fasting twenty-four hours, at the expiration of which time I obliged him to fwallow a number of fmall fpunges. As his ftomach retained thefe very readily and without any apparent inconvenience, I fuffered him to remain at reft for three hours, im- mediately after which he was killed. From thefe fpunges I obtained about half an ounce of very pure gaftric juice. In it I immerfed a common earth- worm. The animal writhed about, and fhewed fymptoms of great distress. I corked the phial, and being at fome distance from home, walked with it in my pocket to my residence. At this time I ex- amined it again ; exactly half an hour had elapfed from the time of my placing it in the phial. The animal fhewed no fymptom of life, and on taking it out of the phial, I found on its body evident marks of violent inflammation. Sufpecting this, however, to be the confequence of the heat of my pocket, which (as it was in the month of April) I believe to have been about 80 of Fahrenheit, I re- peated the experiment. The animal after be- ing immerfed in the gaftric juice, at the tempera- ture of 70 of Fahrenheit, for fifty minutes, fhewed no figns of life; but there was no inflammation evident, as in the former. Knowing, however, that thefe animals live in a temperature ftill lower than this, I determined again to repeat the experiment. To effect this I placed an earth-worm in the phial of gaftric juice as before, and covered it over with the fame 37 fame fod and in the fame fpot from which the ani- mal was taken. Fahrenheit's thermometer flood in the turf at 60. In an hour I examined the phial, took out the worm, and found it lively and not in the leaft injured; but on increasing the temperature to 70, it died as the lafl. Hence we may infer, that this animal alfo refifts the action of the gaftric juice while living and at its own temperature. How far this will be found to be the cafe with other ani- mals, I am at prefent unprepared to decide. I am aware that, according to the experiments of Dr. Stevens, a living leech, which fome perfons have fuppofed to be an animal destitute of pores and capa- ble of fuftaining a degree of heat equal to the hu- man temperature, is digefted by the human fto- mach.* But, that they are capable of fuftaining this degree of heat, I am not fatisfied; at leaft, of this we may be certain, that the tem- perature, at which they ufually live, is not by any means as high. I had rather prefume, that as in my experiments, the animal in this inftance, had died previous to its being acted on by the gaftric juice. Plot does indeed tell us, that he has feen the eyes of a carp and the nofe of a roach, which were taken out of a jack-fifh, digefted, wmle they were yet alive.f And Cornelius is likewife faid to have found a fnake half digefted in a bird's ftomach, while life in that animal was ftill perceptible. In • Vid. his Inau~. Differ, pub. at Edin. in 1777. f Vid. Plot's Staffordlhire. Ch. 7. Se drachms of this mucus, which I had procured from the ftomach of a subject, who had died of a fall. Both flafks were placed in a fand bath, which was kept as nearly as poflible at the temperature of the human body. In feven hours, the one containing mucus emitted air bubbles and fmelled four, where- as the one without mucus had no appearance of fermentation for feveral hours after. 4th. Of the Bile. The name of bile, has been uniformly given to a peculiar fluid, exclufively found in animal bodies, and which is fecreted from a gland of a fingular ftrudture, called the liver. It is more or lefs of a yellowish-green colour, of a difagreeable bitter tafle, of a thicker consistence and more plastic than faliva, of a fingular aromatic fmell when eva- porated, which has been compared to that of mufk, and which is by fome thought agreeable. Bile differs from all other fecreted fluids in the body, in this, that it is not like them, feparated from florid arterial blood, but is fecreted from the dark coloured blood of the vena portarum, which is nothing more than a large veffel, made up by the concurrence of all the veins of the vifcera of the abdomen, (except thofe of the liver,) which empty their blood into it for the purpofe of fecretion. Now a plentiful fupply of blood to a gland, being effential to the fecretion of a fluid, and this blood being 41 being conveyed to the liver by the vena portarum, it has, and I think with propriety, been faid, to perform the office of an artery. It ramifies every where throughout the fubftance of the liver, and terminates in two very different kinds of veffels. The one returns the blood, which is no longer fit for fecretion, again into the general circulation; the others are the fecretory veffels. In the former cafe, the extremities of the vena portarum inofcu- late with thofe of the hepaiic veins, and thus the blood is returned to the inferior or afcending cava. In the latter, the fecreting veffels foon terminate in the pori biliarii, by the union of which, in their paffage out of the liver, trunks of a larger fize are gradually formed, tili at length they terminate in one of confiderable magnitude, known by the name of the hepatic duft. This dua in its turn, foon terminates in another, which has gotten the name of the ductus communis choledochus, in con- fluence of its being the common duct of the liver and gall-bladder, through which bile is con- tinually distilling into the duodenum, in which in- testine this duct ends. Juft however where the hepatic duct ends, and where the dudus communis choledochus begins, another dud arifes, which extends to the gall-bladder, from whence it has received the name of ductus cyfticus. The fecretion of bile, is a subject as yet involved in confiderable obfcurity. While fome phyfiolo- F gifts 42 gifts have considered it as the effect of a peculiar fecretion in the liver, others of equal reputation, have afferted, that it is found formally in the blood. The correctnefs of thefe affertions are only to be determined by experiment, as therefore I cannot do this at prefent, I fhall not venture a conjecture on the subject. The bile being once fecreted, it is received by the fmall branches of the hepatic duct called pori biliarii, from whence it paffes into larger branches, till at length it gradually arrives at the great trunk of the hepatic duct; from thence it paffes through the ductus communis choledochus, and is finally difcharged into the duodenum. This is the moft common courfe of the bile, but if from any fpafmodic affection or morbid distention of the duodenum, or from any obstruction in the ductus communis choledochus its paffage fhould be preven- ted, a retrograde motion of this fluid is the confe- quence. In this cafe it regurgitates through the cyftic duct and finds its way into the gall-bladder, which is a very convenient receptacle, destined to prevent the hepatic duct from being furcharged with bile, in cafes either of obstruction or of too great fecretion. Cyftic bile differs, it appears, from hepatic, in this, that its consistence is mere grumous, it is of a darker hue, and has a more pungent bitter tafte. They do not differ in their constituent parts, but only in the proportion of thofe parts. In fact I do 43 I do believe, that the only material difference which exists between them, depends on the more aqueous part of the cyftic bile being abforbed, from its con- finement and stagnation in the gall-bladder. Two caufes concur to promote the difcharge of cyftic bile. The one is, the preffure which the gall-blad- der receives from the neighbouring parts, and par- ticularly from the ftomach when distended with food; the other, that either from the acrimony which bile acquires by stagnation, or from the mere stimulus of distention, a contraction of the mufcu- lar coat of the gall-bladder will be induced, and its contents will thus be readily propelled into the duodenum. From the experiments of the moft accurate che- mists, the constituent parts of the bile appear to be, i. A coagulable lymph, 2. A refinous matter, 3. Animal gluten, 4. Soda, and 5. A colouring matter, which is believed to be iron. Neither of thefe component parts of the bile is prefent in a perfectly free and difengaged ftate; they are all fo combined as to form an apparently homogeneous fluid. Bile, without the afiiftance*ftf an interme- dium, is not mifcible, as far as I know, with any volatile or fixed oil, with animal fat, nor yet with butter or any other oleaginous fubftance. Neither does it appear to render thefe fubftances mifcible with water, although perfectly fo itfelf. I have feen fome of the bile of an ox, which had been mixed in a phial with an equal quantity of olive oil, and which 44 which after having been kept for more than twelve months and frequently agitated, had not the least difpofition to unite with it. The idea of its render- ing oils mifcible with water, appears to have arifen from its being long fince ufed in the cleaning of fluffs, and hence it has been fuppofed to act chemi- cally and in the fame manner in which foap does. It does I believe act chemically, but ftill not in ex- actly the fame manner in which foap does. Soap is faid to have an attraction for both oil and water, and thus renders them mifcible; whereas, bile by having a greater attraction for the fluff to be cleaned, than oil has, only tends to difplace it, and it is in this way that I believe it always acts, when ufed to re- move fpots of oil, or other greafy matter, from fubftances to which they are adherent. The ufe of the bile in the animal ceconomy is evi- dently material, and I may add, it is singularly im- portant in the procefs of digeftion. I do not how- ever believe, that it has any effect in this procefs while going on in the ftomach, as its prefence in this organ is the confequence of regurgitation, and is without doubt morbid. This I infer, first, from the ficknefs of ftomach, vomiting, vertigo and other fymptoms of great morbid action, which attend its prefence in that organ. And fecondly, from thefe fymptoms being fpeedily relieved, by fuch medicines as effect its difcharge. Doctor Monro having caught feveral frogs, at different times killed three of them, and as fpeedily as 45 as poflible emptied the contents of their gall-blad- ders into the ftomach of another. The confequence of this was, that the animal died fhortly after.* I do not attempt to prove any thing more from this, than that there is fomewhat deleterious in the bile of thefe animals, particularly as we are aware that the bile of other animals have been taken not only with impunity, but even with advantage. I have poured the recent cyftic bile of a cat down the throat of a puppy, without his fuffering the leaft inconvenience from it; and I have feen a black fervant whofe taste had become fo vitiated, after having accustomed himfelf to take the bile of an ox frequently as a stomachic, that he became fond of it," and fo far from its proving injurious to him, he al- ways thought himfelf much better after ufing it. Bile neutralizes both the vegetable and mine- ral acids and is itfelf decompofed by them. In the duodenum, by mixing with the chymous mafs difcharged from the ftomach, it first begins tofepa- parate the chyle from it, and being itfelf decom- pofed, its more aqueous part unites with the chyle, while its refinous adheres to the faeces giving them their natural yellow colour ; thus the former is prepared to undergo the round of the circulation, the latter to be difcharged from the body- » Dr. Wiftar's Lc&ures. 4$ " A further ufe of the bile," fays an admired author, " is, to evolve and exterminate from the " alimentary canal, the fixed air, which had been " hitherto confined among the chymous mafs."* Again, it prevents the too great accumulation of mucus in the intestines, and by its stimulus increaf- es their peristaltic motion. Hence it is that biliary obstructions are generally accompanied with cof- tivenefs, and fometimes with adifcharge of mucus. The property of being both powerfully antifep- tic and antizeumic, is likewife faid to be poffeffed in an efpecial manner by the bile. Maclurg tells us, that " this fluid after having remained to his " knowledge, for three days in a dead body, and " although when the gall-bladder was taken out, " there was a very offensive fmell in all the abdo- " minal vifcera; yet this fluid, being poured into " a phial, and clofely flopped, acquired a fweet " fmell, which continued fome days before the " putrid fetor began."f This property of bile has been fuppofed to be intimately connected with its bitternefs. Knowing, however, that bile is fecreted from the dark coloured blood of the vena portarum, (which is entirely free from any changes effected by air, through the medium of the lungs, and infactpof- fefling all the characters of common venous blood,) does it not appear probable, that its antifeptic qua- lity depends on its attraction for, and confequent abforption * Blumenbach. f Vid. Treat, on the Human Bile. p. 76. 47 abforption of, oxygene. The opinion that the blood, by its circulation through the abdominal vifcera, receives a putrefcent tendency, appears to be erro- neous, as it is deprived of its oxygene and confe- quently becomes antiputrefcent; for bodies can only become putrid by the abforption of this gas. The difference which exifts between the blood of a foetus, which is appropriated to the fecretion of bile, and that of an adult, appears to be wor- thy of fome attention. The difference is briefly this, the blood, from which the bile of a foetus, is fecreted, partakes more of the quality of arterial blood than that of an adult; this likewife makes a proportionate variation in the properties of the bile, and confequently that of a foetus is of a more putrefcent nature, or in other words, has lefs ten- dency to resist putrefaction. The quantity of this fluid fecreted feems evi- dently to be great, particularly when we consider the vaft apparatus of its fecretory organ, and the quantity of blood conveyed to it for this purpofe. Indeed Dr. Monro tells us, that four ounces of cyftic bile have flowed through an ulcer of the fide daily.* 5th. Of the Pancreatic Juice. The juice denominated pancreatic, is a limpid fluid, which bears a greater refemblance to faliva * Vid. Syftem of Anatomy. Vol. II. P- 389. 48 faliva than to any other fluid in the human bo- dy. It is fecreted from a long and flat gland of the conglomerate kind, which lies under the fto- mach, and between the liver and the fpleen, and which is known to anatomists by the name of the pancreas. The fituation of this gland in the abdo- men is tranfverfe, being in the duplicature of the pofterior portion of the mefocolon. It is found not only in man, but in moft other animals, in quadrupeds, in birds, and in many fifhes. The external appearance of the pancreas, is that, of one uniform fubftance, with its furface fomewhat uneven from a confiderable number of fmall convexities, and refembling very much in its flructure the falivary glands. In the centre of the breadth of this gland, we find its great duct run- ning in a longitudinal direction, and into which feveral fmaller ones empty themfelves on each fide,' like fo many minute branches inofculating with one parent ftalk. It has very properly gotten the name of the pancreatic dud, and opens generally in com- mon with the ductus communis choledochus into the duodenum, for the purpofe of emulging its con- tents. This however is not always found to be the cafe, as it fometimes opens by a feparate duct into that intestine. An exaft analysis of the pancreatic juice, as far as I know, has never yet been made ; but, like moft of the fluids of the human body, it is found to 49 to contain common fait and fal-ammoniac. The difficulty of procuring a fufficient quantity of this fluid, I believe, is the reafon, why its analysis has not hitherto been much attended to. We are di- rected to obtain it by inferting a fmall tube, to which a phial is appended, into the pancreatic dnct of a living animal; but this cannot be fo rea- dily accomplifhed, as we may at first fight imagine. The ufe of this fluid is not perfectly understood. It is generally believed to have the effect of dilut- ing the chymous mafs, after its having paffed into the duodenum from the ftomach, and to aflimilate it to an animal nature. Likewife to dilute and at- tenuate the bile, which is fometimes too vifcid and acrid. From analogy the quantity of this fluid fecreted appears to be very great; as the pancreas is no lefs than three times as large as the falivary glands, and has every circumstance as favourable for the fecreti- on of its fluid. Like other glands in the body, its fecretion is increafed by ftimulants, which no doubt makes a very confiderable variation in the quantity fecreted at different times. The preffure which this gland receives from the ftomach when distended with food; the irritation of the cfi/ne in its paffage into the duodenum ; and even that of the bile itfelf, tends to promote the difcharge of its juice. Like the bile, Haller fays,* it is capable of being regur* gitated into the ftomach. G SECTION * Element. PhyfioL T«n. VI. page 309. 5° SECTION III. —§^<€s— HOW FAR SOLUTION IS ADMISSIBLE IN DIGESTION. TO affert that folution does not take place in digestion, would be to deny every thing like testi- mony in medicine. My attempt will only be to fhew, why it is not probable that it can be the fole efficient caufe of that procefs, and how it fhould be confidered as tending to promote it. By folution we can comprehend nothing more, than fo minute a divifion of the particles of any matter, as to render that matter capable of being diffolved in a fluid; and this too, without effecting any change of its component parts; for no poflible divifion be it ever fo minute can have this effect. Thus, the component parts of water are the fame, whether it be in the ftate of ice or of vapour. If this be a correct definition of what we underftand by the term folution, a folvent in the ftomach can have no other effect on our food, than merely that of feparating it into very minute parts or particles; but this is very far from being all which takes place in digeftion. Such a change muft be effected on our aliment, for the due nourifhment and support of our fyftems, as to convert it into that mild and bland fluid which we denominate chyle. This fluid differs in both its appearance and properties from the matters taken into the ftomach, from which it 51 was prepared, and confequently cannot be the effect of mere folution, by which operation matter may be divided, but I prefume can never be changed in its component parts. Again, chemistry has not yet taught us that any difference exists between the chyle of carnivorous and that of herbivorous ani- mals, and from the moft direct experiment we learn, that two animals of the fame fpecies being fed, the one on the matter of a mufcular fibre, and the other on farinaceous matter, both afforded chyle in no refpect different from each other.* Whereas, could chyle be produced by mere folution, it fhould furely differ in its properties, in proportion to the variety of matter from which it is prepared. From thefe facts it appears, that the aid of fome other operation is requifite to explain the formation of chyle. Perhaps feveral may be found neceffary. In addition to folution, I do believe, that fermenta- tion has likewife a very confiderable effect. By it we know, bodies not only become decompofed and re- duced to their elementary principles; but, by a recombination of thofe principles another fubftance is formed, differing materially from that from which it was obtained. It is by a fimilar decompo fition and recombination of the elementary princi- ples of food, together with its fubfequent mixture with certain fluids of the prima? via?, that I believe it becomes fo far animalized and changed in its pro- perties * Fordyce on Food, p. 143- 52 perties as to form chyle. That by the combination of bodies another is formed, differing in its proper- ties from either of thofe of which it is compofed, is too true to be denied. Thus, if we combine with a proper proportion of hydrogene and carbone, a certain proportion of oxygene, we obtain sugar, a fubftance differing very effentially from either of the other three. The effect of folution not being that of a change of the component parts of food, it is clear that its only operation in digestion muft be, that of expediting fermentation. This opinion, if we judge from analogy, I prefume will be found correct. In similar circumftances out of the body, the more minutely any matter is divided which is capable of fermentation, the more fpeedily will that matter go through its feveral ftages. To re- turn to our fimile of fugar. If we diffolve this fubftance in water, its particles may be fo minutely divided as not to be perceptible in that fluid, yet by evaporation the fame fugar may be obtained, not at all changed in its properties. But if we fuffer fugar to ferment, the refult will be very dif- ferent. It will be refolved into its elementary prin- ciples, carbonic acid will be difengaged, and we will likewife obtain alcohol. Here then is a decom- pofition and recombination of its elementary prin- ciples. Sugar being compofed of oxygene, hydro- gene, and carbone, and thefe elements being fepa- rated by fermentation, are re-united to form thefe two 55 two fubftances, to wit, the oxygene unites with a part of the carbone and is difengaged in the form of carbonic acid, while the remainder of the car- bone is diffolved by the hydrogene and forms the alcohol. Thus we fee the material difference in the effects of folution and fermentation. —^^^J— SECTION IV. —&•*<€— WHY IT IS PRESUMABLE THAT FERMENTATION TAKES PLACE IN DIGESTION. WE have already confidered digestion a priori; that is, we have inveftigated the caufes which in- fluence digestion. We have taken notice of the fe- veral properties of the matters which have the moft material effect in this procefs. And we have like- wife feen, that all the circumftances effential to fermentation, are poffeffed in an efpecial manner by food in the ftomach. We have feen, for inftance, that it is plentifully supplied with moisture, not on- ly from our drinks, but even from our faliva and the fluids of the ftomach itfelf; that it receives a fufficient quantity of air from our faliva, by which fluid it is enveloped and continually conveyed into the ftomach ; and laftly, that its fituation is admira- bly adapted to be fupplied with the neceffary quan- 54 tity of heat; on all of which circumstances fermen- tation in a particular manner depends. We have alfo fhewn, that faliva and the mucus of the primas via?, have a confiderable tendency to pro- mote this procefs. Having proceeded thus far on our fubject, it next becomes neceffary, that we consider digeftion a pof- teriore ; or, in other words, that we attend to the effects produced by the digeftion of food in the fto- mach. But in the firft place, we fhall fay a few words on fermentation. Fermentation is that great agent in nature, by which bodies are rendered totally different in their chemical properties, and which, from the variety of its products, has been long fince divided into three feveral stages ; to wit, the vinous, the ace- tous, and the putrefactive. From the first of thefe proceffes we obtain, alcohol; from the fecond, vi- negar ; and from the third, ammoniac; by which means we are able always to afcertain, the nature of whatever fermentation has taken place. It will be recollected, that thefe feveral stages of fermentation are capable of taking place, entirely independent of each other. Whenever the faccha- rine principle of any matter predominates, the vi- nous fermentation will take place ; when the mu- cilaginous is moft abundant, it will undergo the acetous; and when a greater proportion of gluten is prefent, it will run immediately into the putre- factive 55 factive ftage of fermentation. From this it appears, that on the feveral proportions of faccharine matter, of mucilage and of gluten, which any fubftance contains, depends the priority of the fermentation which will commence. Thus it is, that the vinous fermentation is capable of preceding the acetous, and vice verfa. But they do not neceffarily follow each other. Hence it is, that old and generous wines, in which the mucilaginous principle had been de- flroyed, are no longer capable of becoming acid, without the addition of a certain proportion of gum- my matter.* Neither does milk afford a vinous fpi- rit by its own fpontaneous change, as in this cafe it lofes its faccharine principle. Different gafes are difengaged, during the pro- grefs of thefe feveral stages of fermentation. The na- ture of thefe depend on the matter fermented. Thus, in the vinous and acetous ftages of fermentation, carbonic acid is difengaged ; while in the putrefac- tive, azote, carbonated hydrogene gas, fulphurat- ed hydrogene gas, and phofphorated hydrogene gas, are all occafionally evolved. ' We will now confider how far thefe gafes, as well as the other produfts of fermentation, can be confidered as being evolved in the prima? via?. In support of the firft of thefe pofitions, we have that common fact, of our perceiving confiderable eructations of air in affedions of the ftomach. Here it * Chaptal', Chcm. Vol. HI. FaSe a6S' 5* it may be faid, that the difengagement of air is the confequence of difeafe. To this I anfwer, that the eructation I confider as fuch, but not the formation of air. In affections of the ftomach from gout, the quantity of air difengaged is fometimes very great, yet we cannot fuppofe that it is formed by this affection. I regret that I cannot from my own experiments, fay any thing relative to the nature of the air, which is evolved in the ftomach during digeftion. To place this matter, however, in as clear a light as I am able, I fhall take the liberty of making a quotation from Plenck.* This gentleman informs us, that, " in a very healthy man, frozen " to death by cold on a winter's night, there was " found a mixture of four kinds of air in theprimse " viae. " Fixed air was found in the greatefl quantity in " the ftomach, and but little in the fmall intestines. " Vital air was contained chief! iny the ftomach, " and fmall intestines, and, " Azote, and carbonated inflammable air, in " the large intestines." To thefe I may add, that fulphurated hydrogene gas, and phofphorated hydrogene gas, have been proven to be difengaged in crepitu. It appears from the works of Van Helmont, that he was the firft perfon who fuggefted the idea of the prefence of an acid in the ftomach. His opi- nion * Treat, on the human fluids, page 141, 57 nion has been affented to by Haller, who relate*, that the acetous fermentation is very prevalent in the ftomach ; that an acid is fpontaneoufly evolved before putrefaction, and even fometimes refills that procefs. He indeed mentions an acid being detect- ed in the ftomachs of ruminating and of omnivorous animals, in thofe of birds and even of carnivorous animals.* Moft perfons have witneffed the prefence of an acid in their ftomachs. But here an objection arifes. It has been faid, that whenever an acid is prefent in the ftomach it is morbid, and indicates the djfeafed ftate of that organ. When accompa- nied with eructations, I believe this to be the cafe ; as the quantity then appears to be preternatural, and is attended with an inverted peristaltic motion of the ftomach, which is certainly the effect of mor- bid action.. But we muft not infer from hence, that the prefence of an acid in the ftomach, is the effect of difeafe, as I hope to fhew that it is detected in that organ, in the moft found and na- Jural health. This has been proven by Dr. Rufhf many years ago. He has fhewn us by feveral well directed experiments, that he always detected the prefence of an acid in the contents of the ftomach, when thrown up by an emetic, three hours after food was taken; but as it has been objected to his H experiments,, * Elcmen. Phyfiol. Tom. VI. p 140 and 141. f Inaug. Differ, de Coctio. Cib. in Vent. 58 experiments, that the acidity proceeded from the emetic tartar, which had been decompofed in the ftomach, I fhall endeavour to fuperfede this diffi- culty. A gentleman in perfect health and capable of ruminating, dined on roasted beef, Irifh potatoes and leavened bread. His drink was nothing but water. In four hours after, he brought up a por- tion of his dinner. It had an acid tafte, and turned a blue vegetable fubftance of a red colour. The fame gentleman having dined on boiled mutton, cabbage and leavened bread, and having drank water alone, as before, in four hours after, ruminated again. The portion of food brought up had an acid tafte, and, as the laft, turned a blue vegetable fubftance of a red colour. Thefe experiments were frequently repeated after having dined on different fubftances, and with uni- form fuccefs. It was obferved, that the acidity was not as perceptible to the tafte in an hour or two after having dined, as it was in feveral hours after. Thefe experiments may be readily repeated, as I do believe, that ?lmoft any perfon with a little trouble, may learn to ruminate. Again, to determine whether an acid is evolved in the digeftion of a cat, one was fed on boiled beef and Irish potatoes. In five hours after, it was strangled. Its abdomen was opened and its fto- mach taken out, having previoufly placed ligatures on 59 on its two orifices. The food had become foft and pulpy, and there was very little of any kind of fluid in the ftomach. Some of this pulpy mafs being placed in a glafs veffel and mixed with a little water, fhewed evident marks of acidity. It very fpeedily restored the yellow colour of paper stained with rhubarb, after its having been turned brown by an alkali. I am not ignorant of the affertion of Dr. For- dyce, that in his experiments on dogs, cows, and fheep, he could not find the leaft trace of acidity in the duodenum ;* neither could it have been ex- pected othewife, fince, as has been already related, the bile has the effed of neutralizing acids, and of confequence as that fluid is almoft always flowing into the duodenum, the quantity of acid muft be unufually great to be deteded in that intestine. It is a prevalent opinion, that the acid which is prefent in the ftomach is the phofphoric, and con- fequently that it is not the effed of fermentation. But, as it is our duty not to admit either one pofition or another, unlefs it is supported by fads or experiments, I fhall relate fuch of thefe as have induced me to prefume, that it is not the phofpho- ric acid which is ufually found in the ftomach. And, ill. The acid found in the ftomach., does not precipitate fugar of lead from its folution in water. ad. " Being * Vid. Treat, on Food. p. 150 and IJI. 6q 2d. " Being faturated with kali, that is, what " was formerly called fixed vegetable alkali, it " produces kali acetatum, formerly called regene- " rated tartar, or fal-diureticus."* Desirous of knowing whether an acid is evolved in the digeftion of animal fubftances, as well as in the former experiments, the gentleman, capable of ruminating, dined on roasted veal alone and drank water as ufual. In four hours after, a por- tion of the contents of his ftomach was brought up. It turned a blue vegetable fubftance of a red co- lour, and had an acid fmell and tafte. I confefs my being at a lofs in this cafe to determine, whether the acid was the effed of the digeftion of the veal, or whether it proceeded from the remains of fome former food. It was my intention to have afcer* tained this point, by repeating the experiment on the fame perfon, after his having fubfifted on ani- l al food for eight or ten days; but, as I have not now as many days previous 10 the delivering in of my p.ece, I fhall be obliged of confequence to decline the idea. The following experiment how- ever, will at leaft adduce probability, in favour of the acid having been evolved by digestion. Having placed too drachms of roasted veal in a glafs veffel, and covered it completely with faliva, k fpontaneoufly became acid, long previous to there being any figns of putrefadion taking place. This fad * Fordyce on Food. p. 148. s* fad is corroborated by the experiments of many authors of reputation. Haller takes notice of it.# Dr. Rufh found that beef acquired an acid tafte and fmell, when expofed for two days to the heat of fummer ;f and Maclurg relates> that a mixture of mutton and water, panes through the acetous ftage of fermentation before it putrefies. J All animal matters when mixed with fermentable vegetable fubftances, have a tendency to promote fermentation, as appears from a number of experi- ments instituted by Pringle, and who likewife adds, that " after fuch mixtures become four they never " return to a putrid ftate, but, on the contrary, « grow more and more acid."§ And yet, fo far from -our finding this ferment to be injurious to digeftion, on the contrary, animal food feems to be the beft adapted for the aliment of dyfpeptie patients. The publication of Dr. Wilfon*s ingenious inau- gural differtation on digeftion, has induced many per- fons to fuppofe, that every idea of fermentation taking place in digestion k unfounded. The Dodor fub- mitted to distillation, the contents of his ftomach, brought up by an emetic four hours after food was taken, with a view of afcertaining, whether he could deted the prefence of fpirit of wine. This he * Vid. Element. Phifiol. Tom. VI. p. 316. f Vid. Inaug. Dif. p. zt. \ Treat, on the bile. -p. 75. § Difeafe* of the Army, Appendix, paper 4, Experiment a*. 6i he could not, and from hence concludes, that fetf. mentation does not take place in digeftion. It will be feen that I have repeated the Dodor's experi- ment, and I am happy to add, with the fame fuc- cefs ; but I fhall not draw the fame conclusions. Being in perfed health, I dined on corned beef, potatoes and leavened bread. My drink was water alone. In four hours after, I took twenty grains of ipecacuanha and brought up the contents of my ftomach. It fhewed evident marks of acidity. On fubmitting it to distillation, a tranfparent and limpid fluid came over into the receiver, which had a tafte fomewhat fweet, and an agreeable flavour; it had not the leaft appearance of fpirit of wine, neither could I deted in it the prefence of an acid. On examining however the refiduum, which had not been evaporated to drynefs, I was not a little fur- prifed to find it ftill acid. A dog was kept fasting for twenty-four hours. He was then fed for two days fucceflively on animal food. Four hours and a half after taking his laft meal, he was killed. The food in his ftomach fhewed evident marks of acidity. On fubmitting it to distillation, I obtained, as in the laft experiment, a tranfparent and limpid fluid, fomewhat fweet, with an agreeable flavour and in no refped different from that which I had obtained from the contents of my own ftomach. From the above experiments we learn, first, that an acid was produced in digeftion as in the former experiments, «3 experiments, and that it was even found in the refi- duum after diftillation ; and fecondly, that fpirit of wine could not be obtained from the food by diftilla- tion ; but by no means that fermentation did not take place. I do not fuppofe that the vinous fermenta- tion in a healthy ftomach, is ever fo complete that fpirit of wine is formed, this would be equally as incorred as to fay, that putrefadion takes place in that organ. Neither can we fuppofe, that fpirit of wine can ever be obtained from any matter, in which the acetous stage of fermentation has been com- pleted and is then prefent. We have already feen that the acetous fermenta- tion is capable of preceding the vinous; it is proba- ble this may be the cafe in digeftion ; nor would it be by any means fingular. In the preparation of koumifs from the milk of mares, a drink much in ufe among the Tartars, the acetous fermentation always precedes the vinous. But admitting that the vinous fermentation does have the priority, eve- ry circumstance, to which our food is expofed in the ftomach, muft tend to hurry it on fo fpeedily to the acetous ftage, as to prevent the former from be- ing at all perceptible. The heat to which it is expofed in the ftomach, is greater than that which is requifite for the vinous fermentation; and this excefs of heat favours the acetous ftage. When fpeaking of the acid formed during digefti- pn in the ftomach, the word evolve has been ufed by u by manyperfons; whenever I have followed them m this refped, it will be recollected that I have aU ways meant, that it w$s evolved by fermentation. I do not fuppofe, that the acid in the ftomach is fim- ply difengaged from our food, as it is from the com- mon fumach when mixed with water, or any other fubftance in which it is very abundant, The quan- tity of acid contained in the food, on which we have experimented, is not fo great that this could have been the cafe; neither can it be obtained from it out of the body by any other means, than by the afliftance of fermentation. It now remains with the reader to determine, whe- ther or not my position is corred, that this acid is the effed of fermentation. Fermentation out of the body, differs from that which takes place in a Jiving ftomach, in this, that the former is fpontaneous; whereas, the latter is induced by all the numerous circumftances in the ftomach, which tend to promote that procefs, and of confequence muft be more fpeedy, Does not the fad of digeftion being more fpee- dy while we are at reft, than during exercife, fa. vour the theory of fermentation ? How fhall we account for that warmth about the region of the ftomach, fo perceptible in fome per, fons for feveral hours after death, unlefs we admit of fermentation ? Whether we fhall ever be fo fuccefsful as to imi- tate nature in digeftion, as in many of her other operations, 65 operations, I am unable to decide; but, I flatter myfelf, time, that corred difcerner of truth and error, will dired the attention of fome more fortu- nate experimenter to this fubjed, and diflipate eve- ry doubt which may ftill involve it. Having thus delivered my obfervations and expe- riments on digeftion, in as concife a manner as my time would admit of, I fhall now clofe this effay ; but to do this without an acknowledgment to the Feveral Medical Profeffors of this University, would be a breach of that duty which my feelings claim. To you, gentlemen, at leaft this fmall tribute of my esteem is due. Permit me then to prefent you with the fincere acknowledgments of a pupil, for the many opportunities of improvement which your ledures have afforded him. With the affurance of my willies, that you may continue to enjoy all the pleafure of fuccefs in the fcience of medicine, I now bid you, adieu. FINIS, McuL Mist. Mb Qr<5 &> &a. 1*00 H