456 DIGESTION 



These observations made on cats and other laboratory animals no 

 doubt also apply in the case of man. Removal of the contents of the 

 cardiac and pyloric regions separately with a stomach tube after feeding 

 with a test meal part of which was colored with carmine or charcoal, 

 has shown that none of the coloring material was present in the contents 

 of the pyloric end up to twenty minutes or so after the food had been 

 taken. It then appeared but at first only in traces. Another important 

 distinction between the food in the two portions of the stomach relates 

 to its consistency. In the pyloric end it is semifluid and homogeneous 

 in character; in the cardiac end, on the other hand, it is a lumpy, rather 

 incoherent mass. 



The gastric movements must greatly facilitate the digestive processes 

 in the stomach. In the cardiac part the undisturbed condition of the 

 food will, as we have seen, facilitate the digestive action of ptyalin, 

 whereas in the body of the stomach the peristaltic waves, besides mov- 

 ing the food onward, will tend to bring fresh portions of mucous mem- 

 brane and food in contact, so that the latter becomes more thoroughly 

 mixed with the pepsin and hydrochloric acid. In the pyloric part, where 

 no hydrochloric acid is. secreted, the contents, already sufficiently acid 

 in reaction, become more thoroughly churned up with the local pepsin 

 secretion, so that proteolytic action progresses very rapidly. 



The peristaltic waves also facilitate absorption from the stomach of such 

 substances as glucose in concentrated solution and, probably, of hydro- 

 lyzed protein; water, however, is not absorbed. One effect of such 

 absorption is the production of gastrin, which we have seen is the hor- 

 mone concerned in maintaining the gastric secretion after the psychic 

 flow. The fact that the mucosa of the vestibule has, relatively to the 

 cardiac end, few secreting glands is in harmony with the view that 

 absorption is an important function of this part of the stomach. 



THE EMPTYING OF THE STOMACH 



The Control of the Pyloric Sphincter 



When digestion has proceeded far enough in the stomach to bring the 

 food into a homogeneous, souplike fluid (chyme)', portions of this, as they 

 are driven against the pyloric sphincter by the peristaltic waves, instead of 

 being returned as an axial stream into the stomach, are ejected into the 

 duodenum. 



We must now consider the mechanism by which the pyloric sphincter 

 opens to permit the passage of the chyme. Bombardment by the peri- 

 staltic waves is evidently not the cause of its opening, for, as we have 



