498 LECTURE XXI. / - 



oesophageal and gastric fistulas in a dog. Before the animal is fed, no 

 gastric juice flows out of the latter. When the animal is offered food, 

 first of all the dog chews it; on swallowing, instead of reaching *the stomach, 

 the food passes out through the fistula in the oesophagus. Thus there 

 is no chemical, thermal, or mechanical stimulation produced upon the 

 mucous membrane of the stomach. Notwithstanding, five or six minutes 

 after the animal is offered food, there takes place regularly an abundant 

 secretion of gastric juice. Pawlow and Schumow-Simanowskaja * have 

 also succeeded in proving that the vagus nerve carries secretory fibers. 

 The production of gastric juice is not entirely dependent upon the vagus 

 as is evident from the fact that it continues after both the vagi have been 

 severed, although the quality of the secretion is apparently changed; at 

 least, there is less pepsin in it. 



Highly important is the observation that psychic influences have the 

 decisive effect upon the formation of gastric juice. It may be shown that 

 the action of the nerves of taste and of smell alone do not suffice to cause 

 a secretion from the lining of the stomach. Similarly the act of chewing 

 is ineffective of itself. The reflex secretion of the stomach juices is only 

 effected when the animal has the desire to eat. If, after the latent 

 period of about five minutes, the secretion of gastric juice has once begun, 

 it then continues for two or three hours. This secretion produced reflex- 

 ively ceases immediately on cutting the two vagi nerves. It would be 

 wrong to assert that the nerves of smell and of taste take part in the psy- 

 chical stimulation of the secretion. To be sure, they may aid indirectly 

 in many cases, by recalling to the imagination certain impressions which 

 awaken the desires to eat. Of course these impressions may in some cases 

 be first caused by the momentary stimulation of smell or taste. 



By means of such experiments as those carried out by Pawlow in many 

 directions, the great importance of the appetite has been clearly estab- 

 lished. It is by no means a matter of indifference whether one eats with 

 pleasure or from compulsion. 



The importance of the gastric secretion produced reflexively by psy- 

 chical influences is made very clear by the following experiment performed 

 by Pawlow. He took two dogs, each having fistulas in the oesophagus and 

 in the stomach, and introduced equal-sized pieces of meat through the 

 gastric fistula of each dog in such a way that the animal was not conscious 

 of the operation. One of the dogs was then given a piece of meat to devour. 

 (In such cases, where the food devoured does not reach the stomach of the 

 animal, we speak of a fictitious meal.) After some time had passed, Pawlow 

 compared the pieces of meat in the stomachs of the two dogs. It was 

 found that the meat in the stomach of the dog which had received the 



1 Arch. Anat. Physiol. 1896, 53. 



