DIGESTION. 181 



tween the qualities of the nutritive materials in 

 their original, and in their assimilated state. 

 The conversion of vegetable into animal matter 

 necessarily implies a considerable modification 

 of properties ; but even animal substances, how- 

 ever similar may be their composition to the 

 body which they are to nourish, must still pass 

 through certain processes of decomposition, and 

 subsequent recombination, before they can be 

 brought into the exact chemical state in which 

 they are adapted to the purposes of the living 

 system. 



The preparatory changes we have lately been 

 occupied in considering, consist chiefly in the 

 reduction of the food to a soft consistence, which 

 is accomplished by destroying the cohesion of 

 its parts, and mixing them uniformly with the 

 fluid secretions of the mouth ; effects which may 

 be considered as wholly of a mechanical nature. 

 The first real changes in its chemical state are 

 produced in the stomach, where it is converted 

 into a substance termed Chyme; and the process 

 by which thi& first step in the assimilation of the 

 food is produced, constitutes what is properly 

 termed I>igestion. 



Nothing has been discovered in the anato- 

 mical structure of the stomach tending to throw 

 any light on the means by which this remark- 

 able chemical change is induced on the materials 

 it contains. The stomach is in most animals 



