The Physiological Basis of Thirst. 



299 



were washed out with a weak novocaine solution. The immediate effect in 

 these circumstances was doubtless due to the water in the solution, but since 

 the relief lasted much longer than when water was used, the anaesthetic was 

 also a factor. This experience agrees with that of Lipidi-Chioti and Fubini, 

 mentioned earlier. No water was drunk by me during the period of atropine 

 effect, and yet when that effect disappeared, and the saliva flow was 

 re-established, thirst also was abolished. The relation between thirst and 

 such drug action has been noted before, but so strong has been the theory that 

 thirst is a " general " sensation, that the drug has been supposed to produce 

 its effect not by local action but by central changes and by alteration of the 

 blood.* 



Similar in character to the thirst which results from the action of atropine 

 is that which accompanies anxiety and fright. The effect of such emotional 

 states in causing inhibition of salivary secretion is well known. It was the 

 basis of the ancient " ordeal of rice " employed in India as a means of 

 detecting the guilty one in a group of suspected persons. It is illustrated in 

 these days by Heche's report of the effects of air raids on the people of 

 Freiburg-in-Baden, in whom the signs of great fear — chattering of the teeth, 

 pallor, and diarrhoea — were attended by intense thirst.f The unquenchable 

 nature of the thirst which results from terror is a large part of the toiment 

 suffered by the novice in public speaking. 



On the basis of the foregoing evidence I wuuld explain thirst as due 

 directly to what it seems to be due to — a relative drying of the mucosa of the 

 mouth and pharynx. This may result either from excessive use of this 

 passage for breathing, as in prolonged speaking or singing, or it may result 

 from deficient salivary secretion. In the latter case " true thirst " exists, but 

 it is not to be distinguished, so far as sensation is concerned, from " false 

 thirst." True thirst is dependent on the fact that the salivary glands, which 

 keep the buccal and pharyngeal mucosa moist, require water for tlieir action. 

 According to the observations and inferences of Wettendorff, the osmotic 

 pressure of the blood is maintained, in spite of deprivation of water, by the 

 withdrawal of water from the tissues. The salivary glands are included 

 under " tissues," and they appear to suffer in a way which would support 

 Wettendorff's view, for in the presence of a general need for water in the 

 body, they fail to maintain the normal amount and qualityj of secretion. The 

 same is doubtless true of other glands. The importance of this failure of 



* See Sherrington, ' Schafer's Textbook of Physiology,' London, vol. 2 p. 9&1 (1900). 

 + Hoche, 'Med. Klinik,' vol. 13, p. 906 (1917). 



X There is evidence that, as the quantity of saliva diminishes, its water content is less ; 

 i.e., it is more viscous. (See Tezner, 'Arch. Intern, de Physiol.,' vol. 2, p. 153.) 



