298 



Major W. B. Cannon, 



The relation between the decrease of salivary flow in these experiments 

 and the sensation of thirst was quite definite. In the experiment illustrated 

 in fig. 1, for example, the feeling of being " thirsty " was absent until the 

 secretion of saliva began to decline, after 11 o'clock. From that time onward 

 the back of the throat began to feel dry ; there was frequent swallowing, 

 and both the movements of the tongue and the act of deglutition were 

 associated with a sense of " stickiness," a lack of adequate lubrication of the 

 parts. All of this unpleasantness and discomfort disappeared after the 

 restoration of the saliva flow by drinking water. 



The increased spontaneous activity of the tongue and the repeated swallow- 

 ing motions as " thirst " became more marked are noteworthy. These 

 movements are a slight stimulus to salivary secretion, and they have, 

 furthermore, the obvious efiect of spreading about any fluid that might be 

 present. In the absence of sufficient fluid, however, they augment the 

 disagreeableness of the condition by making prominent the friction due to 

 lack of lubricant. The " lump in the throat," which is complained of by 

 persons who suffer from extreme thirst, can be explained as due to the 

 difficulty encountered when the epiglottis and root of the tongue are rubbed 

 over the dry back wall of the pharynx in attempts to swallow. 



The only statement that I am aware of, which is contradictory to the 

 evidence just presented, is that made by one of a group of psychologists, 

 reported by Boring.* This one observer testifled that when he was beginning 

 to be thirsty the saliva flow was still copious. The eight other observers of 

 the group speak of thirst as being characterised by dryness of the roof of the 

 mouth, dryness of the Hps, the sensation of having a " dry sore throat," feelings 

 of stickiness, and uncomfortable " puckery " pressure localised in the middle 

 and back of the tongue and in the palate— in other words, as one of them 

 summed up his experience, "dryness expresses the complex as a whole." 

 This body of testimony agrees closely with that presented earlier and suggests 

 that there may have been error in the one observation that thirst was 

 associated with free secretion of saliva. 



Other evidence on the relation between absence of saliva and the presence 

 of thirst as a sensation was obtained through checking salivary secretion by 

 atropine. Before the injection the amount secreted during 5 minutes by 

 chewing averaged 13"5 c.c. After the full effect of the drug was manifest, the 

 amount fell to 1 c.c. All the feelings that were noted in ordinary thirst — 

 the sense of dry surfaces, the stickiness of the moving parts, the difficulties of 

 speaking and swallowing — all were present. These disagreeable experiences, 

 constituting the thirst sensation, disappeared as soon as the mouth and throat 

 * Boring, ' The Psychological Eeview,' vol. 22, p. 807 (1915). 



