MECHANICAL PHENOMENA. 21 



for the flow of juice from the pancreas. 1 As the acid in the 

 duodenum becomes neutralized the stimulus to the closure 

 of the pylorus is weakened until the acid in the stomach 

 once more opens the sphincter. Another portion of food 

 in consequence escapes from the stomach, the pylorus closes 

 once more, and the cycle is repeated. 



Automatically, therefore, carbohydrates which are not 

 acted upon by the gastric juice leave the stomach soon after 

 ingestion and quickly, while proteins which are digested 

 in this viscus are retained and discharged only slowly. The 

 intestine is spared in this way large doses of acid stomach 

 contents which unless neutralized interfere so markedly 

 with the digestive functions of the intestine. 



The behavior of fat differs a little from that of the carbo- 

 hydrates and proteins. The immediate but slower discharge 

 from the stomach is explained in part by the small amount " 

 of gastric juice which is poured out upon fat. The gastric 

 peristalsis after a meal consisting mainly of fat is also not 

 as vigorous as that found after a meal of protein or carbo- 

 hydrate. Moreover, as soon as fats enter the duodenum they * 

 cause the same closure of the pylorus which is caused by 

 acids. 2 In this way the fats are kept for a long time in the 

 stomach. 



1 See Chapter XII, Part* 2, 4 and 5. 



2 LiNTWAREW: Biochemisches Centralblatt, 1903, I, p. 96, quoted 

 by CANNON. 



