DIGESTIVE SECRETIONS AND THEIR CONTROL 437 



The Control of the Gastric Secretion. Our present knowledge 

 of the mechanism for controlling the secretion of gastric juice is 

 the result of some of the most interesting investigations of modern 

 Physiology. Many workers have had a share in the solution of 

 the problem but the name of one of them, the Russian physiologist 

 Pawlow (Pavloff), is more closely associated with it than that of 

 any other one man. Pawlow's chief contribution was the demon- 

 stration that the secretion of gastric juice is in its early stages ex- 

 cited reflexly, and by only one particular sort of stimulus, namely, 

 the psychical state accompanying the eating of food which is 

 enjoyed. Pawlow gained this information through feeding ex- 

 periments on dogs which had been prepared in a special way for 

 the study. The preparation consisted of making a fistulous open- 

 ing into the stomach, through which the secretion of gastric juice 

 could be followed, and of cutting the esophagus in the neck and 

 bringing the cut ends to the surface in such fashion that all the 

 food swallowed reappeared at the upper esophageal opening, and 

 none reached the stomach unless it was placed within the lower 

 section of the esophagus through its opening. Dogs thus operated 

 upon recovered promptly and completely and could be studied 

 very satisfactorily. It was found that one of these dogs would 

 eat with the greatest enjoyment, although none of the food 

 reached the stomach, and that within a few minutes of the be- 

 ginning of eating a secretion of gastric juice began to be poured 

 into the stomach. That this secretion was excited reflexly was 

 proved by cutting the vagus nerves, after which it never appeared. 

 That it depends upon a certain psychical state, and not upon the 

 mere eating of food was shown in various ways. Dogs which were 

 not hungry would chew and swallow food, but without signs of 

 much interest in it; no secretion was evoked. Meat which had 

 been boiled till it was tasteless was eaten without the production 

 of a secretion. These results make it clear that the stimulus is a 

 psychical one, and that it depends upon active enjoyment of food. 

 Equally important is the observation, made upon these same dogs, 

 that unfavorable emotional states prevent the secretion of the 

 juice. If the dog was angered while eating no juice appeared; 

 even the presence of an attendant for whom he had an aversion 

 sufficed to prevent the secretion. All these facts, established first 

 upon dogs, have been proved true likewise for human beings. 



