486 



DIGESTION 



these and many other observations it is certain that the emptying of the 

 stomach does not at all depend on the operation of the force of gravity. 

 Indeed, that this can not be the case is perfectly clear when we con- 

 sider the disposition of the stomach in quadrupeds. 



Exact observation on the movements which the stomach performs from 

 the time it is filled with food till it empties, have been made by the 

 x-ray method, first introduced by Cannon. 15 The method consists in feed- 

 ing the animal with food that has been impregnated with bismuth sub- 

 nitrate, then exposing him to the x-ray and either taking instantaneous 

 photographs of the shadows or observing them by means of a fluorescent 

 screen. In the accompanying figure (Fig. 155) the outline of the shadow 

 cast by the stomach is shown at intervals of an hour each during diges- 

 tion. Soon after the stomach has become filled, peristaltic waves are 



seen to take their origin about the middle 

 of the body of the viscus, and to course 

 toward the pylorus. The region above the 

 origin of these waves that is, the cardiac 

 half of the body of the stomach and all the 

 fundus, often called the cardie pouch is 

 free from peristaltic Avaves but is the seat 

 of a tonic contraction which as digestion 

 proceeds presses steadily with increasing 

 force upon the mass of food and delivers 

 it slowly to the lower and more active por- 

 tion of the stomach. 



As the food passes into the lower part 

 of the stomach, the cardiac pouch becomes 

 gradually reduced in size until finally when 

 the stomach is empty its outline, as re- 

 vealed by radiographs, departs from the pyri- 

 form shape characteristic of the full organ to assume a more or less 

 tubular form. 



From this description it is evident that the function of the cardiac 

 portion of the stomach is to serve as a reservoir for the food which by 

 a slow contraction of the gastric wall is gradually delivered into the 

 lower and more motile portion of the stomach. The motor phenomena 

 of this portion are of a complex nature and will now be considered. 



Cole, 30 by the employment of serial x-ray photographs taken at short 

 intervals has shown that this portion of the stomach undergoes a succes- 

 sion of rapid changes in shape (Fig. 156), due to the peristaltic waves 

 which course over this region toward the pyloric sphincter. The waves 



Fig. 154. Schematic outline of 

 the stomach. At C is the cardia: 

 F, fundus; I A, incisura angularis; 

 B. body; PC, pyloric canal; P, 

 pylorus. The antrum is the portion 

 from IA to PC inclusive. (From 

 Cannon.) 



