438 DIGESTION 



observed animals in which not only a miniature stomach had been made, 

 but a fistula into the main stomach as well. The .behavior of the secre- 

 tion of gastric juice as a whole could be followed by collecting that 

 which was secreted in the miniature stomach, for it was shown, in con- 

 trol experiments, that this secretion runs strictly parallel with that in 

 the main stomach, being quantitatively a definite fraction of it — accord- 

 ing to the relative size of the miniature stomach — and qualitatively 

 identical. The miniature stomach, in other words, mirrors the events 

 of secretion in the main stomach. 



It was observed that when the animal was allowed to take the food 

 into the main stomach by the mouth and esophagus, the secretion from 

 the miniature stomach continued to flow until the process of gastric 

 digestion had been completed, a result which was quite different from 

 that obtained after sham feeding. The only possible explanation for this 

 result is that the food in the stomach sets up secretion as a result of 

 local stimulation. To investigate the nature of this local stimulation, 

 Avhether mechanical or chemical, food and other substances were placed 

 in the main stomach through the gastric fistula without the animal's 

 knowledge so as to avoid possible psychic stimulation, and the secretion 

 observed from the miniature stomach. When the mucous membrane of 

 the main stomach was stimulated mechanically, as by placing inert 

 objects such as a piece of sponge or sand in the stomach, no secretion 

 occurred. Evidently, therefore, the stimulus is dependent upon some 

 chemical quality of the food. 



By introducing various foods it was found that there is considerable 

 difference in the degree to which they can excite the secretion. "Water, 

 egg white, bread and starch, were all found to have very little if any 

 effect. On the other hand, when protein thai had been partly digested 

 by means of pepsin and hydrochloric acid was introduced into the 

 stomach, it immediately called forth a secretion. The conclusion is that 

 the partly digested products, even of insipid food, are capable of directly 

 exciting the secretion. These include proteoses and peptones, and it 

 was, therefore, of great interest to find that a solution of commercial 

 peptone is also an effective stimulus. This is a result of deep significance, 

 for it indicates that the food which has been partially digested by the 

 appetite juice will serve as a stimulus to continued secretion. 



The psychic juice has been aptly called the "ignition juice," because 

 by producing partial digestion it serves to ignite the process of gastric 

 secretion. Experimental evidenee of its great importance in gastric 

 digestion was secured by Pavlov in experiments in which he placed 

 weighed quantities of meat attached to threads in the stomaeh through 

 ;i gastric fistula, and after some time removed them and determined by 



