344 



DIGESTION. 



in inspiration, or absorbed in the upper part of the 

 alimentary canal, again to be excreted at a portion of the 

 same tract lower down in either case assuming rapidly 

 a gaseous form after their excretion, and in this way, 

 perhaps, obtaining a more ready egress from the body. 



It is probable that, under ordinary circumstances, the 

 gases of the stomach and intestines are derived chiefly from 

 the second of the sources which have been enumerated. 



Tabular Analysis of Gases contained in the Alimentary Canal. 



The above tabular analysis of the gases contained in the 

 alimentary canal has been quoted from the analyses of 

 Jurine, Magendie, Marchand, and Chevreul by Dr. Brinton, 

 from whose work the above enumeration of the sources of 

 the gas has been also taken. 



Movements of the Intestines. 



It remains only to consider the manner in which the 

 food and the several secretions mingled with it are 

 moved through the intestinal canal, so as to be slowly 

 subjected to the influence of fresh portions of intestinal 

 secretion, and as slowly exposed to the absorbent power 

 of all the villi and blood-vessels of the mucous mem- 

 brane. The movement of the intestines is peristaltic 



