;-w A H I *'.*'-^P -, --v^->t Y, Yr~ ■ u LxQf(_^L..".-'OrC"OfC^ Surgeon General's Office V gSs-r to ■■::..(;! Oaj OjQQC^^CmgQOOjaClO'OiQ^on-g AN Inaugural Experimental DhTertation ON DIGESTION, SUBMITTED TO THE EXAMINATION OF THE tier. JOHN E WIN G, 'S. T. P. P*orosrs THE Trustees and medical faculty OF THE UNIVERSITYoF PENNSYLVANIA, On the 17th day of May, 1796. FOR THE DEGREE OF DOCTOR OF MEDICINE. By yohn TVilfon, A. M. of Penn/y/vania, MEMBER OF THE PHILADEDHHIA MEDICAL SOSIETY. Aggrediar, non tam perficiendi, quam experiendi voluntate. Cic. 0*at. ad Brut. FHllADELTHIA, PRINTED BY LANG Is* USTICh\ \ M.DCC.XCVI. ^ C - TO Cajpar TViJlar, m. d. ADJUNCT-PROFESSOR OF ANATOMY, SURGERY, AND MIDWIFERY, IN THE UNIVERSITY OF PENNSYLVANIA; THIS DISSERTATION IS RERPECTFULLY INSCRIBED, AS A SMALL TRIBUTE OF GRATITUDE AND ESTEEM, BY BIS MUCH OBLIGED FRIEND AND PtfPllj JOHN WILSON. e_ Introdu&ion. OlNCE the works of a Fordyce, a Hunter, and, above all, the ingenious Spallanzani have ap- peared on this fubject, a further inveftigation feemed unneceflary; but as phyfiologifts were not fettled in their opinions, and as fome ufeful experiments have heretofore been neglefred, which might have a ten- dency to throw fome light on fo interefting a fubje£t, this fmall attempt may not prove unacceptable. But notwithstanding this, I am laid under an ob- ligation of an higher nature j as the laws of this Se- minary require that every candidate for medical honours ihould exhibit before the Truftees and Fa- culty, fome evidence of his improvement in the principles cf that art which has been the ground of his ftudies; therefore, neceffity, not choice, prompts the unexperienced Student to attempt the inveftiga- tion of fomething new, or take the tedious round of dull repetition—The former enfuring upon his unde 15 ( 6 ) fended head the piercing ftiaft of criticifm, while the latter is fure to create difguft. In a fubjeft fo difficult and obfcnre as the animal ceconomy, it is not furprifing, that philofophers fliould be fo often embarraffed; and that inftead of certainty, they fliould frequently be obliged to determine her operations by a feeming probability, or by a vague and diftant analogy. All animated beings feem to be fubjecl: to certain laws calculated for the purpofe of their ceconomy. Thefe laws difpofe them to certain modes of action, which occafion a diminution either of their fluids, or folids, or both. Poflibly they may remain in a dormant ftate for fome time without fuftaining any diminution or lofs of fubftance. But when a lofs is fuftained, it is necef- fary, that it fliould be fupplied by the addition of fome new matter. If this matter is different in its qualities from the matter of the body which is loft, it is neceffary that it fliould undergo fome charjge, and be converted into a fubftance endued with the fame qualities, as that which was loft. Befides the continual wafte which animals are fuffering, there is a certain period of their lives in ( 7 ) which they are acquiring new parts, and encreaung thofe already formed. In confequence of this, it is necefTary that food fliould be employed to fupply mat- ter for this formation and increafe. For this purpofe, there is a certain procefs in the organs of digeftion of living animals, through which food has to pafs, before it can be animalized and get into the general fyftem of veffels. It muft, therefore, be prefumed, that food has to undergo fome change, in confequence of its delay in thofe organs. Although the Organs of Digeftion in different animals are fo various, it is moft probable, that thofe changes which take place in the food of different animals are fimilar ; their mode of life only rendering a different apparatus necefTary. But our prefent enquiry is not about the fituation and ftru&ure of thofe organs, or the quantity or quality of food beft adapted to them ; it is about the mode of aflimilating thofe fubftances to an animal nature, whereby a frefti growth of parts may be maintained, or a conftant lofs of fubftance renewed. A N JNAUGURAL DISSERTATION O N DIGESTION. X HE human frame, like every other machine, Would necefTarily wear out by the mutual attrition of its parts, without a conftant renovation. For this purpofe we are endued with the peculiar appetites of hunger and thirfi. The difagreeable fenfations ari- fing from a non-indulgence of thefe, and the extreme pleafure produced by their gratification, ftimulate us to take in alimentary fubftances; and thefe having gone through the procefs of digefiion, are converted into fit nutriment to fupport .the various parts of the body. The fubftances beft adapted to this purpofe are taken from the animal and vegetable kingdoms. Thefe, under various forms and modifications, con- ( io ) ftitute the proper food for the body. But the mode of operation in the procefs of Digeftion, has been a fubje& of confiderable aliercation among phyfio- logifts. Some phyfiologifts have afTerted that the ftomach operates in digeftion principally by a triturating power. Another opinion concerning Digeftion was,y that it is effe£ted by fermentation. Since the experiments of the ingenious Spallan- zani, mechanical agency, by trituration, in the pro- cefs of Digeftion, has no longer any weight among philofophers. It remains, then, to confider what chemical change really does take place, whereby fuch heterogeneous fubftances are reduced to one fimple homogeneous matter, called chyle. This change has been afcribed either to fermentation, or folution, pr both. The do&rine of fermentation was much in vogue about the middle of the laft century, when an expla- nation of the various functions of the human body was fought for in fermentation. It appears that Boerhaave firft oppofed the generally received opi- nion of fermentation in the animal functions, but ftill admitted a limited degree of it in the aft of Digeftion. He fuppofes that nothing prevents a compleat fer- ( " ) mentation of the food taking place in the ftomach, but its fhort continuance there. Some modern phy- sicians, viz. Pringle and M'Bride, think this limitation too great, and maintain that a compleat fermentation really does take place in the procefs of Digeftion. But let us take notice that their experiments were made out of the body, and their conclufions drawn from its being produced in this fltuation by adding faliva to alimentary fubftances. Dr. Rufh alfo appears to conclude in favour of this latter opinion from the like experiments, as well as thofe made in his own ftomach. Indeed, when we confider the circumftances of the food during Digeftion, there certainly is a ftrong prefumption in favour of this doftrine. But notwith- ftanding this, and the nearly convincing arguments of fuch ingenious advocates, I am led to adopt a con- trary opinion from my own experiments, and thofe of others. Befides, the continual influx of frefh humours into the ftomach, and the fhort continuance of alimentary fubftances there, ftrongly induce me to believe that it is not a fermentative procefs. The different fpecies or ftages of fermentation, as defcribed by chemifts, are the vinous, acetous, and ■putrefactive. The putrefactive ftage of fermentation, few, or none, now believe to have any agency in ( ■* ) Digeftion. On the contrary, from a variety of expe- riments made to afcertain this faft, I found that pu- trid aliment is incapable of being converted into chyle before it is fweetened by the action of the gaftric juice upon it. Thofe who argue in favour of the vinous and acetous ftages of fermentation, main- tain their opinion from particular phenomena fre- quently attending the procefs of Digeftion; fuch as acid eru&ations and vomitings, the acid tafte of the gaftric juice, and internal coat of the ftomach, &c. That fuch appearances frequently do take place cannot be denied; but whether they are the natural effects of the digeftive procefs, or unnatural incidental occurrences, owing to a morbid ftate of thofe organs, or to an improper quality or quantity of food, is a matter of contention. To the latter opinion I am ftrongly inclined, both from experiments and other- wife. To difcover whether the quality of food has any influence on the digeftive organs, I fed a number of dogs, for fome time, on animal food alone. They were then killed about four hours after eating frefli animal fubftances, at which time Digeftion was con- fiderably advanced j but neither the gaftric juice of thofe animals, or the contents of their ftomachs fhewed any flgns of acidity when touched with an ( *3 ) infuflon of blue vegetables. According to thofe expe- riments, animal fubftances which feem to be the moft natural food of thofe animals, do not produce the lead acidity in the digeftive organs in a healthy ftate, and ftill digeftion was completely performed. But as uni- formly as I fed them with vegetable, or with animal and vegetable fubftances together, I found an acid to exift in the ftomach and duodenum of thofe animals. I alfo made a number of other experiments differently modified, and they uniformly rendered flmilar refults. Mr. Hunter very properly obferves, " That fer- mentation can go on in the ftomach, there is no doubt; but when this ha ipens, it arifes from the powers of digeftion being defe&ive." Animal Eco- nomy, p. 161. And again, the fame author fays, " That it may be admitted as an axiom, that two procefTes cannot go on at the fame time, in the fame part of any fub- ftance ; therefore, neither vegetable nor animal fub- ftances can undergo their fpontaneous changes, while digeftion is going on in them ; a procefs fuperior in power to that of fermentation." P. 163. Having found, by the former experiments, that an acid is not necefTarily produced in digeftion, I made a number of experiments out of the body with water, C ( H ) faiiva, and the gaftric juice, in di&rent alimentary mixtures, to find at what time fermentation really does begin. Experiment I Equal parts of boiled pork, parfoip and leavened bread, were put into two vials. In one vial water alone was added to thefe fubftances ; in the other equal parts of fajiva, and water. Thefe mixtures were fubmitted to a fand heat equal to the human body. No fermentation was difcovered tili between four and five hours. Air-bubbles firft ap- peared' in the vial, containing faiiva. Experiment II. Leavened bread and boiled pork were put. into two vials. In one vial water was adr ded, and in the other faiiva. Thefe w£re fubmittcd to a heat equal to the human body ; but in neither of thefe could fermentation be difcovered till towards five hours, either by the cfcape of air-bubbles, or by an infufion of blue vegetables. Experiment III, Unleavened bread, roafled beef and potatoe in equal quantity were put into two vials. In one vial water, and the other faiiva, and water were added to thefe mixtures. They were then fubmitted to a fand heat between 960 and 1120 of Fahren- heit's thermometer. A faiall .degree of fermentation was-perceived at the end of four hours. The reafoa ( 15 ) of fermentation beginning fooner in this experiment, than in the former, may be accounted for from the heat being fomething greater than that of the human body.—The vials containing water alone in the fore- going experiments, were ufed only by way of compa- "rifon, and the chief difference appeared to confift in the efcape of air-bubbles, and not in the change of colour produced by an infufion of blue vegetables. Experiment IV. I obtained a quantity of pure gaftric juice from my own ftomach. This I mixed with equal quantities of faiiva and water in fimilar mix- tures with the former experiments, and fubmit- ted them to a heat equal to the human body. They remained much longer than any of the former expe- riments before they fliewed any figns of fermenta- tion. The gaftric juice, in thofe experiments, mewed as ftrong antizymic powers as it had done, in former experiments, antifeptic ; and both powerfully oppofe the doctrine of fermentation, either putrefactive or acetous*, in the procefs of digeftion. Finding that little difference took place, in the former experiments, between alhnentary mixtures with water and thofe with faiiva, I was induced to believe that any other fluid of the body of equal viilklity (the gaftric juice excepted) would (hew figns of fermentation with any alimentary matters, as foon ( 16 ) as with faiiva. I therefore made a number of expe- riments with the ferum of blood alone, and mixed with water, in different preparations, under fimilar circumftances with the former experiments ; but was never able to difcover any difference, either by the efcape of air-bubbles, or when touched with an in- fufion of blue vegetables. I am, therefore, cf opinion with Dr. Fordyce, in oppofition to Dr. M'Bride, that the faiiva has no fer- menting principle ; and he very juftly obferves, that " Dr. M'iiride grounds his opinion on experiments made with pieces of meat and water mixed together alone, and pieces of meat, water and faiiva mixed together in fimilar vials; upon letting them ftand, air-bubbles were found in the vial, in which the meat, water and faiiva were contained, before there were any found in the vial, in which the pieces of meat and wa- ter were alone contained. The refultwasthe fame when bread and water ; and bread, water and faiiva were compared : and alfo, when bread, meat and water ; and bread, meat, water and faiiva were compared. But no deduction can be made from thefe experi- ments, by which the power of the faiiva to induce fermentation can be grounded; becaufe the faiiva giving vifcidity to the water would prevent vapours from rifing in fmall and imperceptible bubbles j and ( *7 ) would retain them until they became more numerous, and until they united together fo as to become more fenfible." Eordyce on Digeftion, p. 53&54-. It may be affced, at what time does Digeftion begin to take place.? From a number of experiments made on dogs to afcertain this point, I found it to be immediately after food had been taken into the fto- mach. Now we know that fermentation cannot take place in any known circumftaces out of the body in lefs than four or five hours, when a ferment is not added, in which time the whole procefs of digeftion is completed. That fermentation may take place to- wards the latter end of digeftion, will not be denied; but this is far from being a necefTary confequence to digeftion, as Dr. Rufli fuppofes : it is nothing more than an accidental circumftance necefTarily taking place from food being too long retained in the fto- mach, when the power of the digeftive organs has been too feeble to affimilate it, before this natural change takes place. To put the fubjeft beyond a1! poflibility of contro- verfy, I inftituted a number of experiments hereto- fore untried, and which were as difagreeable as new. Experiment I. Having breakfafted upon coffee, leavened bread and butter, and a little boiled ham, ( i8 ) fcymyofrelifti—four hours afterwards, I took ah Emetic, which brought up the contents of my ftomach. Thefe I fubmitted to diftillation and re-diftill uion, feveral times repeated; but I could not difcover the Itnalleft appearance of fpirit of wine throughout any part of the procefs. Experiment II. Having dined upon roafted beef, leavened bread, potatoes and water—three hours after I took three grains Of emetic tartar, and threw tap the contents of my ftomach. This appeared acid to the tafte, and imparted a flight red colour to a blue infufion of vegetables, as Dr. Rufh very juftly remarks in his experiments ; but after fubmitting thefe to diftillation, as in the former experiment, I could not produce any figns of fpirit of wine. Thefe experiments, though extremely difagreeable I repeated at a time when I enjoyed the moft per- fect ftate of health, and with exadrdy the fame iffue. Experiment III. But left it fhould be thought that the experiments made on my own ftomach were not fufiicient to eftablifh the doctrine, I obtained the fa- vour of a healthy man in the Houfe of Employment to aflift me. He dined heartily on leavened bread, boiled pork, parfnip and potatoe, and a little water ( >9 ) by way of drink. Thijee hours after he difchsffged the contents, of his ftomach by an emetic, Experiment IV. The fame man having dined upon leavened bread, beef-ftake and molaffes been—• four hours afterwards he took an emetic, and threw up the contents of his ftomach. The two laft expe- rements were* treated by diftillation, fimilar to thofe made on my own ftomach, and with exactly the. feme refult. Thefe experiments appeared fufficient to difprovo the doctrine of fermentation in the procefs of DigeC tion. Neverthelefs, if,the fpirit of wine fhould accident tally appear in diftilling the contents of the ftomach* I could not fubfcribe to the doctrine of fermentation necefTarily having any agency in Digeftion.; becaufe the digeftive organs may be fo flightly debilitated, or be under fo fiaall a degree of morbid excitement, as fcarcely or not at all to be perceived; and under thefe circumftances fermentation of a vinous nature might readily take place. This is a ftate, every perfon is very fenfible, frequently takes place in his ftomach ; but who, under fuch circumftances,. would ever, fup- pofe. this to be either natural or asceflkry to di- geftion .? ( 20 ) In this manner I would account for an acid be- ing produced in the ftomach, when an acetous acid is generated there. Eut, is the acid moft commonly found in the ftomach, the pure acetous, acid ? Is it not more properly called the phofphoric acid, which is evolved in the time of digeftion, or otherwife the carbonaceous matter of the faccharine part of the ali- mentary mixture ftrongly attracYmcv pure oxigene, forming thereby carbonic acid, fo frequently found in the ftomach ?* Now, feeing- we fo conftanfly obferve that fer- mentation, combuftion, and elective attraction pro- duce new and different changes in bodies indepen- dent of each other ; may we not confequently look for other changes to take place in the properties of bodies entirely different from either ? This we fee in the procefs of Digeftion, whereby two or more fub- ftances are decompofed, and re-combined in another * After having written the above pages, I met with the follow- ing Letter de M. Reynior, a M. de la Metherie. The writer cf this letter informs M. de la Metherie, that pro- feflbr Struve and M. Maquart, have difcovered that the phofpho- ric acid and volatile alkali are the two eflential conftituent parts of the gaftric juice ; and M. Struve has compofed a liquor which ads on alimentary matters, in the fame manner as the gaftriq juice. Journal de la Phxfiyvc, C ai ) manner by a procefs fui generis, and thereby forming a tertium quid, poffeffing properties widely different from its conftituent principles. And, as Mr. Hunter obferves, "The procefs of Digeftion differs from every other natural operation in the change of bodies. It is by no means fermentation, though it may fome- what refemble it. For fermentation is a fpontaneous procefs, and is that natural fucceflion of changes, by which vegetable and animal matter is reduced to earth; therefore, mild be widely different from Digeftion, which converts both animal and vegetable fubftances into chyle; in the formation of which, there cannot be a decompofition fimilar to fermen- tation. " Digeftion is very different from chymical folution, Which is only an union of bodies by elective attrac- tion, not a real change of the fubftances themfelves, but of their properties. But digeftion is an aflimila- ting procefs, and in this refpect. is fomewhat fimilar in its action to morbid poifons. It is a fpecies of gene- ration, two fubftances making a third ; but the curi- ous circumftance is its converting both vegetable and animal matter into the fame kind of fubftance or com- pound, which no chymical procefs can effecl:." A queftion may ftill be afked, whence is the acid principle derived which cxifts in the fecretions, par- ( 22 ) iicularly in the Urine, if a fermentative procefs is not admitted in the aft of Digeftion ? To this I anfwer, that all the fecretory organs of the living body appear to pofTefs a power peculiar to themfelves. And is it not an immutable law in animal bodies, that each gland can fecrete no other, but its own proper fluid, which is wholly, or in part, fabricated in the very gland itfelf, by an animal procefs, which it there undergoes ? But why one gland poffefies the power of fecreting a faltifli, another a bitterifh, or another an acid principle, is a difficulty with which the pre- fent ftate of Phyfiology has not made us acquainted, Neverthelefs, we know that all the fecretions of the body are produced from the peculiar matter of blood fpecifically acred upon by the various fecretory organs, They cannot be produced by any other fubftances, or powers, either within or without the body, In endeavouring to explain the modus operandi in the procefs of Digeftion, we fliould conftantly re- member this one principle, that nothing can be cre- ated or annihilated in all the proceffes and operations of nature or art. Neverthelefs, we might almoft be led to a contrary conclufion from obferving the great difference in appearance between aliment before and after the procefs of Digeftion, ( n ) Aliment contains all the elements of chyle as yd\ before as after Digeftion, but in a different ftate of combination. Mr. Boyle has proved that the proper- ties of compound bodies depend upon their principles of combination, and not upon the properties of their elements. For inftance, barley and fugar are' com- pounds of different properties, but by diftillation they yield fimilar elements. In like manner a piece of mufcle pafling through the organs of digeftion pro- duces chyle: now the mufcle and chyle are found by chymical analyfis to yield the fame produces. It ap- pears then, that the mufcle and chyle differ from each other only in their mode of combination. TJje converfion, therefore, of a mufcle into chyle, is a feparation of its elements, and a recombination of them in a different manner ; fo that the new com- pound fhall have new properties, If the changes above mentioned depend upon elective attraction; a queftion may arife, why cannot chyle be produced at any time out of the body, by giving an opportunity for this attraction to a&, or why animal and vegetable fubftances do not always exjfi in the form of chyle ? I anfwer, that when two fubftances have a difpo- fition or power to unite with or decompofe one ano- ther, it is not fufficient that they fhould merely ( «4 ) poflefs the propenfity or even ability of producing the effeft, but likewife be in fuitable circumftances for that power to aft. Thus, for example,- a folution of fugar and water kept in a temperature not exceeding 400 of Fahrenheit's thermometer, will not have its elements to feparate and recombine into wine, but if otherwife, this effeft will be produced. In this manner the aftion of the living ftomach, and other organs of digeftion, upon the food, are indifpenfably necefTary, in order that thofe powers may aft, by which a new ftate of aggregation may be effefted. Food placed in all the chymical circumftances fimilar to thofe in which it is placed in a living fto- mach, would never be converted into chyle, but would undergo other changes totally different. Ani- mal food would putrefy, and vegetable food would become acid. If the living power of the ftomach be ftrong and healthy, food will be perfectly digefted; but if weak, it will go imperfectly through the organs of digeftion, and fome part of it will necefTa- rily undergo thofe changes which it would have undergone in fimilar chymical circumftances; but will not be then afted on by the living organs of digeftion. ( *5 ) For want of this circumftance, chyle never can be produced in any other place than in the organs of digeftion of a living animal. The peculiar ftate of the food produced by the aftion of the living ftomach, without which chyle cannot be formed, is illuftrated by the following chymical faft, viz. Farinaceous matter, mucilage and native vegetable acid, may be combined into wine; but as an indifpenfably neceffary pre-requiflte, they muft be formed into fugar. What- ever may be the reafon or neceflity for this, it is not; eafy to demonftrate ; but moft certainly, it is a caufa fine qua non. Juft fo the food is brought into a .ftate indifpenfably necefTary in the living organs of digef- tion, previous to the formation of chyle, FINIS. heoL. Hist, VslZ. nn ^M ft:# /;. w*V