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Croonian Lecture. — The Physiological Basis of Thirst. 



By Major Walter B. Cannon, M.R.C., U.S. Army ; 

 George Higginson Professor of Physiology, Harvard University. 



(MS. received and Lecture delivered June 20, 1918.) 



A custom which has usually been respected by investigators who in years 

 past have had the high honour of delivering the Crooniau Lecture is that of 

 reporting and interpreting a group of related researches upon which they 

 have been engaged and which they have already made public. That is a 

 custom which I should have been happy to follow on the present occasion if 

 miUtary service had not sharply broken in on my studies months ago and 

 made them seem now very remote and the summarising of them a diflficult 

 occupation. And, after all, is it not natural for us as investigators to hold 

 the forward look, to consider the problems before us rather than those that 

 have been solved ? May 1, therefore, be permitted to bring to your attention 

 some ideas and observations which have not yet been published and which, 

 though incomplete, may prove interesting and suggestive. 



In regarding the human body as a self-regulating organisation we observe 

 that, so far as mere existence is concerned, it depends on three necessary 

 supplies from the outer world, — on food, to provide for growth and repair and 

 to yield energy for internal activities and the maintenance of body heat ; on 

 oxygen, to serve the oxidative processes essential to life ; and on water, as the 

 medium in which occur all the chemical changes of the body. These three 

 supplies are of different orders of urgency. Thus a man may live for 30 or 

 40 days without taking food, as professional fasters have demonstrated,* and 

 suffer no apparent permanent injury to his bodily structure or functions. On 

 the other hand, lack of oxygen for only a brief period may result in uncon- 

 sciousness and death. Indeed, certain nerve cells in the cerebral cortex 

 cannot withstand total deprivation of oxygen for more than 8 or 9 minutes 

 without undergoing such fundamental changes that they do not again become 

 normal when they receive their proper supply .f Intermediate between the 

 long survival without food and the very brief survival without oxygen is the 

 period of existence which is possible without water. Records of men who 

 have missed their way in desert regions and who, with no water to drink, 

 have wandered in the scorching heat have proved that they rarely live under 

 these circumstances of struggle and torrid atmosphere for more than three 



* Luciani, ' Das Hungern,' Leipzig, 1890. 



t See Gomez and Pike, 'Jour, of Exp. Med.,' vol. 11, p. 262 (1909). 



