FUNCTIONS OF ANIMALS. 



every fractured bone, and every wound of the body, is a proof of 

 its existence, and an instance of its action. 



Every organ employed in assimilation has a peculiar office ; 

 and it always performs this office whenever it has materials to 

 act upon, even when the performance of it is contrary to the in- 

 terest of the animal. Thus the stomach always converts food in- 

 to chyme, even when the food is of such a nature that the pro- 

 cess of digestion will be retarded rather than promoted by the 

 change. If warm milk, for instance, or warm blood, be thrown 

 into the stomach, they are always decomposed by that organ, and 

 converted into chyme ; yet these substances are much more near- 

 ly assimilated to the animal before the action of the stomach than 

 after it. The same thing happens when we eat animal food. 



On the other hand, a substance introduced into an organ em- 

 ployed in assimilation, if it has undergone precisely the change 

 which that organ is fitted to produce, is not acted upon by that 

 organ, but passed on unaltered to the next assimilating organ. 

 Thus it is the office of the intestines to convert chyme into chyle. 

 Accordingly, whenever chyme is introduced into the intestines, 

 they perform their office, and produce the usual change ; but if 

 chyle itself be introduced into the intestines, it is absorbed by 

 the lacteals without alteration. The experiment, indeed, has not 

 been tried with true chyle, because it is scarcely possible to pro- 

 cure it in sufficient quantity ; but when milk, which resembles 

 chyle pretty accurately, is thrown into the jejunum, it is absorb- 

 ed unchanged by the lacteals.* 



Again, the office of the blood-vessels, as assimilating organs, 

 is to convert chyle into blood. Chyle, accordingly, cannot be 

 introduced into the arteries without undergoing that change ; 

 but blood may be introduced from another animal without any in- 

 jury, and consequently without undergoing any change. This 

 experiment was first made by Lower, and it has since been very 

 often repeated. 



Also, if a piece of fresh muscular flesh be applied to the mus- 

 cle of an animal, they adhere and incorporate without any change, 

 as has been sufficiently established by the experiments of Mr J. 

 Hunter; and Buniva has ascertained, that fresh bone may, in 

 the same manner, be engrafted on the bones of animals of the 

 same or of different species, f 



* Fordyce on Digestion, p. 189. f Phil. Mag. vi. 308. 



