Medicine, 237 



^. To produce and support animal heat: 3. To 

 impart a quality to the circulating fluid which en- 

 ables it to stimulate the left side of the heart. 



After this account of respiration, which, from 

 its great importance in the animal economy, has 

 been treated of more at large than was at first in- 

 tended, it is proper to proceed to the consideration 

 of Digestion. This function in its full extent in- 

 cludes all the changes which aliment undergoes for 

 the formation of chyle, whether such changes are 

 effected in the mouth, stomach, or small intes- 

 tines. But as it is the knowledge of the office of 

 the stomach which has received the most import- 

 ant improvement within the period assigned for 

 this retrospect, and as the other parts of the pro- 

 cess, such as mastication, deglutition, the admix- 

 ture of saliva, &c. were tolerably well understood 

 before, it is obviously expedient to direct the chief 

 attention to the former branch of the subject. 



Galen supposed heat to be the principal cause 

 of digestion, and this opinion so generally prevailed 

 for a long time that the term coction was used by 

 the greater part of physiologists instead of diges- 

 tion. But, though the effect of heat in assisting 

 and expediting digestion is universally admitted, 

 no person will now contend that it is the sole 

 cause. 



During the eighteenth century, the theorists of 

 digestion have ascribed it either, singly, to fer- 

 mentation, mechanical action, or the operation of a 

 solvent in the stomach; or to the combined effects 

 of- two or all of these agents. 



Dr. BoERHAAVE, dissatisficd with the opinions 

 of all who had gone before him on this subject, 

 and leaning strongly to mechanical theory, ad- 

 mitted fermentation as one cause of digestion, but 

 principally ascribed it to trituration, pressure, and 

 powerful quassation. The analogy of digestion. 



