A custom which has usually been respected by investigators who in years past have had the high honour of delivering the Croonian 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 military service had not sharply broken in on my studies months ago and made them seem now very remote and the summarising of them a difficult 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 unconsciousness 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. 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 days, and many die within 36 hours. An exceptional instance has been reported, of a Mexican, who, lost in the dry plains of the south-western part of the United States, walked, or crept on his hands and knees, between 100 and 150 miles, repeatedly drinking his own excretions, and succeeded, after nearly 7 days wholly without water, in reaching a habitation. This is a record which, for its conditions, has no parallel. If the thirsting man is not subjected to heat or exertion his life may continue much longer than 7 days. Viterbi, an Italian political prisoner, who committed suicide by refusing food and drink, died on the eighteenth day of his voluntary privation. After the third day the pangs of hunger ceased, but, until almost the last, thirst was always more insistent and tormenting. He records again and again his parched mouth and throat, his burning thirst, his ardent and continual thirst, his thirst constant and ever more intolerable. Thus though the period of survival varies, death is sure to come whether food, or oxygen, or water is withheld.
Croonian Lecture.—The physiological basis of thrist