202 PHYSIOLOGY AT THE FARM. 



merits performed on persons in whose stomachs a communica- 

 tion existed with the external air. Similar experiments may 

 be made, out of the living body, by means of an artificial 

 gastric juice. This artificial gastric juice is made by macerat- 

 ing in water portions of fresh or recently dried mucous mem- 

 brane of the pig, or of the fourth stomach of the calf, and 

 adding to the infusion a few drops of hydrochloric acid. 

 Portions of aliment introduced into such a fluid and exposed 

 for some time, as an hour or more, to the temperature of 100 

 F. that, namely, of the warm-blooded animal body become 

 softened and otherwise changed, much in the same manner as 

 in the living stomach. 



The mode in which such changes are effected on the aliment 

 in the stomach is hardly understood. It may be supposed 

 that the pepsine of the gastric juice acts a part like that of a 

 ferment in setting up the requisite changes ; but the process 

 nevertheless differs essentially from the ordinary forms of fer- 

 mentation. Whatever alters the composition of the pepsine 

 for example, excess of heat, strong alcohol, and powerful acids 

 puts an end to its digestive quality. 



The change which the aliment undergoes in the stomach is 

 its conversion into chyme. The signification of chyme, how- 

 ever, is not very well defined. What the stomach gives up to 

 the duodenum is not a homogeneous substance. The significa- 

 tion commonly attached to chyme is probably that it is the 

 portion of the aliment which has undergone complete solution 

 in the stomach ; but what the stomach surrenders to the 

 duodenum is composed in part of aliment which has under- 

 gone complete solution, together with substances more or less 

 changed, that are to go through further changes in the duo- 

 denum under the influence of the bile, the pancreatic juice, 

 and the proper intestinal secretion, and lastly with substances 

 that, being unsusceptible of alteration within the living system, 



