DIGESTION 



185 



FIG. 88 



pylorus, for some of the food taken into the now distended stomach 

 went directly into this portion of the viscus, no dividing line between 

 fundus and antrum being as yet present. Soon, however, the antrum 

 begins to be shut off from the fundus by contraction of its sphincter, 

 and it remains a distinct portion of the stomach until the viscus is quite 

 emptied into the duodenum. This is a period which varies with the sort 

 and amount of food eaten, from one to seven or even more hours. The 

 movements of the antrum are rhythmically peristaltic, and they serve by 

 their strong compression against the resisting pylorus to grind and squeeze 

 whatever lumps of food may be present and are not too hard into a 

 soft pultaceous mass. The con- 

 tained pepsin, the hydrochloric 

 acid, the mucus, and the heat 

 of the organ materially aid in 

 this process of chymification. 

 The antrum contracts in the 

 cat about once in ten seconds, 

 according to Cannon, probably 

 as a continuation of the peri- 

 stalsis over the fundus, said by 

 Lommel to occur in the dog 

 somewhat less frequently. The 

 small intestine is much more 

 delicate and sensitive than is the 

 stomach, and would be disturbed 

 not a little by the reception of 

 lumps or hard masses of solid 

 food. 



The pyloric valve opens peri- 

 odically and in a rhythmic way. 

 It is actuated by probably ner- 

 vous influences sent out from 

 the antrum's walls. It is stim- 

 ulated to relaxation, that is, to 

 open (according to Cannon), by 

 strong acidity in the antrum, 

 and it is closed by acidity in 



the duodenum beyond it. Thus, in cats fed on a proteid meal the form- 

 ing chyme remains much longer in the antrum than when the food is 

 carbohydrate. Protein does not absorb the free acid of the stomach as 

 carbohydrate does, thus leaving the acid free to stimulate the pylorus 

 to contraction. The carbohydrate takes large quantities of the acid 

 early into the duodenum, and its presence there keeps the valve shut. 

 The proteid has thus longer time for digestion in the antrum. To 

 remain there would be useless in case of carbohydrates. Every two or 

 three minutes, however, in the cat, the pyloric valve relaxes and allows 

 part of the liquid portion of the chyme to escape into the intestine. The 



Gizzard of a bird: A, contracted state; 

 B, relaxed state. (Jarrod.) 



