422 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The pepsin is only released when the strongly alkaline reaction of the 

 lower portion of the small intestine dissolves the bile precipitate. It 

 can then do no harm, as pepsin is inactive in alkaline solutions ; while, on 

 the other hand, the acid does not interfere with the pancreatic digestion, 

 since the pancreatic ferments are still capable of producing their charac- 

 teristic effects, even in a faintly acid medium. 



The acid reaction of the small intestine is most marked in carniv- 

 orous animals, and in them, consequently, putrefactive and fermentative 

 changes occur to a less degree than in omnivora and herbivora. In the 

 fasting horse the contents of the small intestine are invariably alkaline, 

 this reaction being more marked the greater the distance from the stom- 

 ach. In digesting animals, the acid reaction decreases below the point 

 of entrance of the bile and pancreatic juice, and becomes decidedly alka- 

 line at the lower portion of the small intestine. This holds in the horse, 

 ox, and sheep, whether fed on dried or green fodder, on oats, grain, or 

 roots. The cause of the alkalinity of the reaction of the intestinal con- 

 tents is due to the bile, pancreatic juice, and intestinal secretions, and is 

 more marked the more active is intestinal digestion. The acidity of the 

 intestinal contents when present is due not only to the acid gastric 

 juice, but also to the liberation of fatty and lactic acids from lactic and 

 butyric acid fermentations. 



It is seen from the above that in the small intestine secretions are 

 met with which are capable of establishing digestion of the various food- 

 stuffs, so as to render them capable of absorption. Starch becomes con- 

 verted into sugar through the action of the pancreatic and intestinal 

 secretions ; cane-sugar is converted into invert-sugar through the action 

 of the special ferment of the intestinal secretion ; fats are partially 

 saponified and emulsified through the influence of the bile and pancreatic 

 juice, while albuminoids, through the influence of the pancreatic and 

 intestinal fluids, are turned into peptones. , ' 



As regards the changes which occur in albuminoids in the small 

 intestine, it is worthy of note that in all probability the formation of 

 leucin and tyrosin haslbeen greatly overestimated, for since the intestinal 

 juices are almost always acid, and since leucin and tyrosin only form 

 in alkaline digestive juices, perhaps these bodies never form normally in 

 the intestine. It is, at any rate, certain that but mere traces of leucin 

 and tyrosin are to be found in the intestinal contents during digestion 

 of large amounts of albumen. It is also worthy of note that the acid 

 reaction of the intestine does not interfere with the digestion of fats, for 

 the laetenls will be found filled with a milky emulsion after feeding, even 

 though the reaction of the intestinal contents is almost as acid as the 

 gastric juice. 



At the lower end of the small intestine the reaction of the intestinal 



