376 A MANUAL OF PHYSIOLOGY 



an excitant to all the gastric glands. The cardiac mucosa was 

 found incapable of forming this substance. 



It is not to be imagined that the ' psychical ' secretion and the 

 secretion called forth by the direct action of the food or food- 

 products in the stomach perform independent offices. They can, 

 in various instances, be shown to supplement each other. For 

 example, not more than one-half or one-third of the gastric 

 juice secreted during the digestion of bread or boiled egg-albumin 

 can be ascribed to the psychic effect. Yet these substances, when 

 introduced directly into the stomach, cause practically no secre- 

 tion. We must suppose that during the digestion of the bread 

 ind albumin by the psychically secreted juice certain products 

 analogous to those in the meat extract are formed, which act as 

 chemical excitants of the local secretory apparatus. The psychic 

 juice is indispensable in this case to start the process, ' to set the 

 stove ablaze,' as Pawlow puts it. In the case of meat it is not 

 indispensable, since the meat can chemically excite the gastric 

 glands ; but it greatly hastens the process of digestion. These 

 facts emphasize the importance of appetite in digestion, a truism 

 in treatment which thus receives for the first time a rational 

 explanation. The influence of good-humour upon nutrition, which 

 experience has crystallized into the proverb ' Laugh and grow 

 fat,' has also been shown to depend in great part, at least upon 

 a beneficial action on the . digestive functions, both motor and 

 chemical. The movements of the cat's stomach and intestines 

 have been observed to cease when the animal became angry 

 or excited by unpleasant emotions ; and in a dog whose gastric 

 glands were pouring out a copious psychical secretion in response 

 to a sham meal, secretion stopped abruptly when the animal's 

 wrath was awakened by what is probably to the normal dog 

 the most specifically * adequate ' stimulus for the emotion of 

 anger the sight of a cat which he was restrained from chasing. 



By means of experiments with the miniature stomach it has 

 been further shown that each kind of food has its own charac- 

 teristic curve of gastric secretion. With flesh diet the maximum 

 rate of secretion occurs during the first or second hour, and in 

 each of the first two hours the quantity of juice furnished is 

 approximately the same. With bread diet we have always a 

 sharply-indicated maximum in the first hour, and with milk a 

 similar one during the second or the third hour (Fig. 146). 

 The juice secreted on different diets also differs in digestive 

 power i.e., in the amount of protein which a given quantity of 



acts as a chemical messenger in exciting the activity of some more or less 

 distant organ. The classical example is the pancreatic secretin which, 

 manufactured in the intestinal mucosa. excites the secretion of the pan- 

 creatic juice. 



