THE REGULATION OF GASTRIC SECRETION 203 



tervals of one or two seconds invariably yields a secretion of 

 gastric juice from the stomach. The negative or at best 

 uncertain results of the older observers upon stimulation 

 of the vagus are probably all to be explained by the fact that 

 their animals were under the influence of anaesthetics or in 

 pain, and, as will become apparent when the pancreatic 

 secretion is described, peripheral stimuli of various kinds'^ 

 inhibit markedly the activity of the digestive glands. When 

 all peripheral stimuli are prevented from inhibiting reflexly 

 the activity of the stomach (this can be done by dividing the 

 spinal cord just below the medulla oblongata), the vagus 

 nerves may be laid bare in the neck and stimulated at once, 

 when a secretion of gastric juice will be observed. In this 

 way USCHAKOFF has succeeded in demonstrating, in an experi- 

 ment performed at one sitting, the relation of the vagus nerve 

 to the stomach. 



Both forms of experiment, the "chronic " as well as the 

 "acute/ 7 show, therefore, that the vagus nerve contains fibres 

 which influence the secretion of the gastric glands. As will 

 be shown later, however, a secretion of gastric juice occurs 

 also when the vagi are cut; this indicates that the integrity 

 of the vagus is not the only requisite for the secretory activity 

 of the stomach. Under normal circumstances, however, these 

 nerves play the already described exceedingly important role 

 in the initiation of the gastric flow. 



4. The Appetite as an Excitant of Gastric Secretion. 

 It was shown in the preceding paragraphs that the vagus 

 . nerve has a marked influence upon the secretion of juice by 

 the stomach. We have now to answer the question, How 

 is the vagus nerve normally excited? An explanation which 

 first suggests itself is that we are dealing with a reflex excita- 

 tion of the gastric mucosa, brought about through a stimula- 

 tion of nerve endings in the mouth and carried from here to 

 the vagus centre in the medulla, and from there down- 

 ward to the stomach. This idea has been carefully tested 

 experimentally by PAWLOW and found to be incorrect , as shown 



