NERVOUS SYSTEM UPON SECRETION 173 



the animal, in addition to being shown the food, was allowed to 

 chew and swallow it ; but the food dropped out at the oesophageal 

 fistula, and did not enter the stomach and so excite it by direct 

 contact. In this method of sham feeding the flow of gastric juice 

 was somewhat greater in most cases than where the afferent 

 stimulus occurred from the sight of food only ; but the increase 

 was never very marked, and in the case of some foods which greatly 

 excited the appetite, the psychical juice or " appetite juice " was 

 as great or even exceeded slightly that from sham feeding. 



Again, Pawlow was able to study by this method the effect 

 of stimulation of the gastric mucous membrane by means of direct 

 contact of the food, which was introduced into the stomach through 

 the gastric fistula without the knowledge of the animal, when it 

 was asleep, or when its attention was strongly excited in some 

 other direction. In this case there is an absence of the ordinary 

 excitants of appetite in the sight and smell of food, and in the 

 operations of chewing and tasting it. Here it was found that the 

 effect upon secretion varied with the character of the food, and 

 that contrary to what might perhaps have been expected, digestible 

 proteid food did not always prove to be a strong excitant to a 

 flow of gastric juice. Thus milk or a solution of white of egg intro- 

 duced into the stomach gave rise to scarcely any secretion, not 

 any more than a quantity of water or dilute saline solution. But 

 meat broth, meat juice, or solutions of meat extracts gave rise 

 in all cases after a latent period of a few minutes to a considerable 

 flow of gastric juice. The number of such direct excitants of a 

 flow of juice was, however, found by Pawlow to be small, being 

 almost confined to certain constituents of flesh food, which are 

 also found in meat extracts. Thus, fats, carbohydrates, and 

 ordinary proteids were without any effect. 



In the case of flesh food, Pawlow showed that the amounts 

 of secretion obtained by sham feeding and by direct introduction 

 of the flesh into the stomach, when added together approximately, 

 equalled the amount of secretion when the animal ate the food, 

 and the food which dropped out at the oesophageal fistula was 

 placed in the stomach. 



>,, Accordingly the excitation to secretion through the nervous 

 system may be divided into three fractions : viz. (1) that due to 

 the sight and smell of the food ; (2) that due to the taste, mastica- 

 tion, and swallowing of the food ; and (3) that due to the contact 



