436 DIGESTION 



it, these animals did not produce any appetite juice. In one animal that 

 showed considerable liking for bread, active secretion occurred when he 

 was fed with this foodstuff. 



Pavlov further noted that usually it was not necessary actually to 

 allow the animal to take the food into his mouth, but that mere teasing 

 with savory food was sufficient to cause the secretion, and that in 

 highly sensitive animals even the noises and other events usually asso- 

 ciated with feeding time were sufficient to excite the secretion. In the 

 case of a hungry animal, the mere approach of the attendant with food, 

 or some other noise or action definitely associated with feeding time, 

 was sufficient to excite the secretion. The appetite juice when started 

 was found to persist for some time after the stimulus causing it had 

 been removed. 



Carlson has succeeded in confirming in man most of these observa- 

 tions. He noted, however, that the secretion produced by seeing or 

 smelling or thinking of food is much less than would be expected from 

 Pavlov's observations on dogs. Even when his subject was hungry, 

 Carlson did not observe that the bringing of a tray of savory food into 

 the room caused any secretion of gastric juice. It is, of course, to be 

 expected that the quantity of the psychic secretion will not be the same 

 in different individuals. It has been observed, for example, by Pavlov 

 to vary considerably in the case of dogs, and it is very likely that it will 

 vary still more in man, with his more highly complicated nervous system. 

 In no case could Carlson observe any secretion of gastric juice produced 

 by having his patient chew on indifferent substances, or by stimulating 

 the nerve endings in the mouth by substances other than those directly 

 related to food. 



In man the rate of secretion is proportional to the palatability of the 

 food, the smallest amount, during twenty minutes' mastication of pal- 

 atable food, being 30 c.c. and the largest 150 c.c., in a series of 156 obser- 

 vations. A typical curve showing the amount of the secretion is given 

 in Fig. 149. To construct this curve the gastric juice was collected dur- 

 ing five-minute intervals while the man was chewing a meal of average 

 composition and of his own choice. An interesting feature depicted on 

 this curve is that the secretion rate was highest in the last five-minute 

 period, this being the time during which the dessert was being taken, 

 for which this man had a great relish. Quite clearly there was a direct 

 relation between the rate of the secretion of the appetite juice and the 

 palatability of the food. It will further be observed that it took only 

 from fifteen to twenty minutes after discontinuing the chewing before 

 the juice returned to its original level. 



The practical application of these facts in connection with the hygiene 



