DIGESTION 



the gastric juice is due to hydrochloric acid, which exists in the proportion 

 of about two parts in 100 of the juice, though occasionally the butyric or 

 phosphoric acid may be also present. In addition to the acid there is also 

 a ferment named pepsine, and the acid and the pepsine together are the 

 main agents in the process of gastric digestion in the adult horse. In the 

 foal there is a second ferment, which coagulates and acts on the casein of 

 milk. The action of the ferment and acid is chiefly exerted upon the 

 proteids or nitrogenous constituents of the 

 food, which it causes to swell up, dissolve, 

 and undergo a chemical change into soluble 

 peptones. 



In regard to the oils, the only change 

 that takes place in them in gastric digestion 

 is that their cell walls are dissolved and the 

 oil set free; and although no chemical action 

 is exerted upon the oil, the constant churn- 

 ing movements to which the food is subjected 

 by the stomach reduces it to the condition 

 of an emulsion. The starches are not acted 

 upon by the gastric juice, but the food is so 

 thoroughly impregnated with saliva that pro- 

 bably the action of that fluid is continued in 

 the stomach. Solution and absorption of 

 peptones, salts, and sugars takes place to a 

 certain extent in the stomach, but a portion 

 of these substances mingled with the emulsi- 

 fied oils filter through the pyloric orifice into 

 the duodenum, or first part of the intestine. 

 Towards the close of digestion the pylorus 

 or right opening of the stomach relaxes to 

 a greater degree, and the remains of the meal enter the intestine. 



Gastric digestion in the horse lasts about three hours, but is accelerated 

 if water is ingested. The observations of Colin show that the successive 

 portions of food swallowed retain to a considerable extent the order in 

 which they have been ingested, and do not mix together much if no water 

 is given. 



Intestinal digestion. — As soon as the chyme has passed from the 

 stomach into the intestine it excites the flow of bile from the liver, of pan- 

 creatic juice from the pancreas, and of intestinal fluid from the numerous 

 Lieberkuhnian follicles and glands of Brunner that are distributed through 

 the mucous membrane. All these fluids are alkaline, and hence the reaction 



-Section through the Duodenum, 

 showing" Brunner' s Glands 



A, Villus. B, Follicle of Lieberkiihn. 

 C, Muscularis mucosae. D, Brunner's 

 gland. E, Connective tissue. P, Mus- 

 cular coat. 



