301 ^^od. 



Di«"estion3 therefore^ is not completed in this orffan ; for tlie 

 chyme passes from the stomach into the intestines, and is there, by 

 mixing with the bile, converted into two substances of very different 

 )iinds, namely, chyle and excrementitious matter. 



The chyle must, in fact, be considered the immediate matter of 

 nutrition. For, as we know that the blood is the magazine, from 

 whence the waste of all the fluids, and the wear and tear of the solids 

 are supplied, so, we also know, that the chyle makes good the per- 

 petual demands that are made upon the stock of blood, by becoming 

 converted into the latter fluid. But, how chyle, which is white, 

 and resembles milk, becomes red blood, or how blood is afterwards 

 (by the process called assimilation) converted into muscle, ligament, 

 tendon, bone, and all the other component parts of an animal 

 body, is a poiat which must be referred to those phenomena that 

 are placed infinitely beyond the ken of human sagacity to reach or 

 to explain. 



Calm reflection might, indeed, have occasioned philosophers to 

 doubt exceedingly (a priori) whether there was any greater chance 

 of solving the phcenomena of digestion, a process intimately con- 

 nected with the very existence of animal life, than of being able ta 

 explain how the brain acts upon the nerves, or the nerves upon the 

 muscles, in the production of voluntary motion. For, though, from 

 the prodigious difference which is found between food and chyme, as 

 well as that which exists between chyme and chyle, there was good 

 reason for supposing that the change effected in both instances, must 

 be of a chemical nature, yet, as chemistry cannot imitate either of these 

 changes, we must infer that they are somehow or other connected 

 with vitality, a power which it will be readily admitted, is beyond 

 the comprehension of our finite faculties. 



