512 THE GASTKIC JUICE [CH. XXXIII. 



glands are under the control of the nervous system, but the early 

 attempts to discover the secretory nerves of the stomach were 

 unsuccessful. The Kussian physiologist Pawlow solved the problem 

 by the employment of new methods. He experimented on dogs. 

 In the first place he separated off the diverticulum, which we 

 described on the last page, and by careful experiments he showed that 

 the secretion of this small stomach is an exact sample, both as regards 

 composition and rate of formation, of that which occurs in the main 

 stomach, which is still left in continuity with the oesophagus above 

 and the duodenum below. 



Another procedure adopted was to divide the oesophagus, and to 

 attach the two cut ends to the opening in the neck. The animal was 

 fed by the lower segment, but any food taken into the mouth, or any 

 saliva secreted there, never reached the stomach, but fell out through 

 the opening of the upper segment. These animals were kept alive 

 for months, and soon accommodated themselves to their new con- 

 ditions of life. The animals could thus be subjected to, (1) real 

 feeding, (2) sham feeding, by allowing them to eat food which subse- 

 quently tumbled out through the neck opening, and (3) psychical 

 feeding, in which the animal was shown the food but was not allowed 

 to eat it. The psychical element is important. 



Mechanical excitation of the stomach wall produces no secretion. 

 If water is introduced there is a slight flow, and even if meat is 

 introduced into the main stomach without the knowledge of the dog, 

 the juice formed is scanty and of feeble digestive power. 



There is, moreover, no connection between the acts of mastication 

 and swallowing with that of gastric secretion. Sham feeding with 

 stones, butter, salt, pepper, mustard, extract of meat, and acid, though 

 it excited a flow of saliva, produced no effect on the stomach. If, 

 however, meat was used for the sham feeding, an abundant and active 

 secretion occurred in the stomach (that of the small stomach was 

 actually examined) after a latency of about five minutes. The 

 secretion is thus adapted to the kind of food the dog has to digest ; 

 the larger the proportion of protein in the diet, the more abundant is 

 the juice, and the richer both in pepsin and acid. 



Indeed, if the animal is hungry and shown the meat and not 

 allowed to swallow it, the effect is almost as great. The following 

 striking experiment also shows the importance of the psychical element. 

 Two dogs were taken, and a weighed amount of protein introduced into 

 the main stomach of each without their knowledge ; one was then sham 

 fed on meat, and one and a half hours later the amount of protein 

 digested by this dog was five times greater than that which was 

 digested by the other. 



In the meat, however, it is not the protein which acts most 

 strongly as the stimulus ; egg-white, for instance, is not a stronger 



