20 



DIGESTION. 



The next experiments which we possess are 

 those of Marcet, who operated upon the chyle 

 as procured from dogs. One main object of 

 his researches was to ascertain how far chyle 

 of animal origin differs from that from vege- 

 tables, and he had the food of the dogs regu- 

 lated accordingly. His results with regard to 

 the general nature and properties of chyle cor- 

 respond very exactly with those of Vauquelin. 

 He found the coagulum to have a pink colour, 

 and to contain a fibrous or filamentous sub- 

 stance, while the liquid part contained a quan- 

 tity of an oily matter, which floated on its 

 surface like cream. This oily matter appeared, 

 however, to be confined to the animal chyle, 

 and it is remarked generally, that this bore 

 more resemblance to blood than the chyle from 

 vegetables. They contained the same saline 

 ingredients, but the solid residuum of the 

 animal chyle was considerably greater; and 

 as the vegetable chyle, when submitted to 

 destructive distillation, was found to contain 

 much more carbon, it was inferred that the 

 animal chyle must have contained proportion- 

 ably more hydrogen and nitrogen.* Upon 

 these experiments we may remark, that the 

 difference between the animal and the vege- 

 table chyle in this case might perhaps depend 

 in some degree upon vegetable food being less 

 adapted to the digestive organs of the dg ; 

 because the chyle of the horse, as examined by 

 Vauquelin, appeared to be more completely 

 animalized, although it must have been derived 

 from vegetable diet. 



The experiments of Dr. Prout agreed gene- 

 rally with those of Vauquelin and Marcet; 

 he found the coagulum and the fluid part 

 analogous to the two components of the blood, 

 and he likewise observed the oily matter. He 

 compared the chyle derived from animal, with 

 that from vegetable food, and detected the oil 

 in both of them, and, upon the whole, he 

 found them to differ less than was supposed 

 by Marcet; he remarks, however, that the 

 latter contains more water and less albuminous 

 matter than the former.f We were likewise 

 indebted to Dr. Prout for an interesting ac- 

 count of the successive changes which the 

 chyle experiences, from its entrance into the 

 lacteals, until it is finally deposited in the 

 thoracic duct, its gradual conversion into 

 blood corresponding to the progress along the 

 vessels.]: 



While the alimentary mass passes through 

 the small intestines, the chyle, as it is separated 

 from it, is taken up by the lacteals, so that 

 when it arrives at the large intestines, nothing 

 remains but the residuary matter, whch is to 

 be discharged from the system ; this consti- 



lin, but they do not contain much precise informa- 

 tion ; Ann. Chirn. t. Ixxx. p. 81 et seq. 



* Med. Chir. Trans, v. vi. p. 618 et seq. 



t In some late experiments which were per- 

 formed by MM. Macaire and F. Marcet, on the 

 origin of nitrogen in animals, they analyzed the 

 two species of chyle, and found them to be nearly 

 the same in their chemical composition, and espe- 

 cially in respect to the quantity of nitrogen which 

 they contained ; Ann. Chim. t. li. p. 371. 



f Ann. Phil. v. xiii. p. 22. .5. See also Magendie, 

 Physiol. t. ii. p. 154. . 8. 



tutes what has been termed the process of 

 defaecation. There can be no doubt that the 

 principal and primary use of the large in- 

 testines is to serve as a depository for this 

 residuary mass, yet there are certain circum- 

 stances in their anatomical and physiological 

 structure, which might render it probable that 

 some farther purpose is served by them than 

 the mere retention of the faeces. Dr. Prout, 

 who has minutely examined the successive 

 changes which the contents of the intestinal 

 canal experience, observes that the secretions 

 even of the rectum still possess the property 

 of coagulating milk, which we noticed above 

 as being one of the most distinguishing cha- 

 racters of the digestive system, so that it would 

 seem that these organs, in some way or other, 

 still assist in the process of nutrition. We 

 may presume, however, that this is only a 

 secondary object, and that the primary use 

 of the large intestines is to serve as a reservoir, 

 in which the faecal mass might be retained, 

 in order to be evacuated at certain intervals 

 only.* (See INTESTINAL CANAL.) 



Before we dismiss this part of our subject, it 

 may be proper to make a few remarks upon 

 two of the abdominal viscera, which, from their 

 anatomical position and their physiological rela- 

 tions, are generally classed among the chylopoi- 

 etic organs, as being supposed to contribute to 

 the function of digestion; these are the pancreas 

 and the spleen. The pancreas bears a very near 

 resemblance to the salivary glands of the mouth 

 and fauces, both from its intimate structure and 

 from the nature of its secretions, and it has been 

 presumed, that it acts in the same manner upon 

 the aliment ;f it must, however, be admitted 

 that we have little but analogy or conjecture in 

 favour of this opinion. 



The spleen is an organ which, both from its 

 size, its situation, and the number of blood- 

 vessels belonging to it, has been supposed to 

 serve some important purpose in the animal 

 economy, and from its apparent connexion with 

 the stomach to be, in some way, concerned in 

 the process of digestion. But although many 



* Prout, ut supra, p. 15 . . 22 ; see also Soem- 

 mering, Corp. Hum. Fab. t. vi. 241. We do not 

 perceive that there is any foundation for the hy- 

 pothesis of Sir E. Home, that the colon is the organ 

 in which the adipose matter is produced, lect. v. i. 

 p. 468 et seq. and Phil. Trans, for 1821, p. 34. 

 Dr. O'Beirne has lately published an essay on the 

 process of defaecation, to which we shall refer our 

 readers, as containing some new views .on the 

 subject. We are indebted to Berzelius for an ana- 

 lysis of the faeces, which appears more minute 

 than any that had been previously made. 



t For an account of the pancreas and its secre- 

 tions we may refer to De Graaf, Tract. Anat. Med. 

 as the first correct treatise on the subject ; to Boer- 

 haave, Prelect. 101, cum notis ; Haller, Prim. 

 Lin. cap. 22. and El. Phys. xxii. ; Simmering, 

 Corp. Hum. Fab. t. vi. p. 142.. 8; Fordyce, 

 ut supra, p. 70.. 2; Biumenbach, Inst. Physiol. 

 24 ; Santorini, tab. 13. fig. 1. Tiedemann and 

 Gmelin have given us the result of their examina- 

 tion of the pancreatic juice, from which they con- 

 elude that it differs in some respects from the 

 saliva ; Recherches, t. i. p. 41, 2. Leuret and 

 Lassaigne, on the contrary, suppose these secre- 

 tions to be very nearly identical j Recherches,. 

 p. 49 et seq. 



