The Physiological Basis of Thirst. 



285 



our bodies the presence of water as the main constituent of the digestive 

 secretions, its role in the chemical changes of digestion, its service as a 

 vehicle of absorption, its importance in the composition of blood and lymph, 

 its use, together with other substances, in body fluids as a lubricant, its 

 action in regulating body temperature — these functions need merely to be 

 mentioned to illustrate how water influences every activity which living 

 beings display. 



Because water is a fundamental essential to life, and is continually 

 escaping from the body, and because there is consequent need for repeated 

 replenishment of the store, an inquiry into the mechanism of the replenish- 

 ment is a matter of interest. 



That such a mechanism exists is indicated by the fact that all our essential 

 functions, leading to preservation of the individual and of the race, are con- 

 trolled not through memory and volition, but by insistent sensations and 

 desires. The unpleasant sensation of thirst causes us to drink. Not towards 

 the subjective aspect of these automatic arrangements, however, is the 

 special attention of the physiologist directed. He is primarily concerned 

 with the bodily states which give rise to the sensation. Only when these 

 states and their relations to the needs of the organism are known is the 

 automatic control explained. 



About six years ago I called attention to some graphic records of motions 

 of the stomach in man which showed that the sensation of hunger is associated 

 with powerful contractions of the empty or nearly empty organ. And 

 because the hunger pang began to be experienced after the contraction had 

 started, the conclusion was drawn that hunger is not a " general sensation," 

 as was formerly held by physiologists and psychologists, but has its immediate 

 origin in the stomach, and is the direct consequence of the strong contrac- 

 tion.* This conclusion has since been abundantly confirmed by Carlson and 

 his collaborators in observations on themselves and on a man with a gastric 

 fistula.f 



Even more imperious than hunger as an insistent and tormenting sensa- 

 tion, accompanied by a dominant impulse which determines our behaviour, 

 is thirst. Indeed, these two experiences — hunger and thirst — are such 

 impelling motives in directing our conduct that from early times they have 

 been used as supreme examples of a strong desire. The ancient prophet 

 spoke of a " hunger and thirst after righteousness " to express the eagerness 



* The Harvey Lectures", New York, 1911-1912, p. 130 — Cannon: Harvey Lecture, 

 December 16, 1911, " A Consideration of the Nature of Hunger " ; also Cannon and 

 Washburn, ' Am. Jour. Physiol.,' vol. 29, p. 441 (1912). 



t Carlson, ' Control of Hunger in Health and Disease,' Chicago, 1916. 



TOL. XC. — B. , 2 A 



