A NORMAL DIET 389 



as much food as men of similar occupation in Holland. Similarly, Kanke, 

 in Munich, found that he required as much food to maintain his body 

 weight in summer as he did in winter. 



The explanation of this uniformity of food consumption over a wide 

 range of external temperatures appears quite obvious. Except under very 

 unusual circumstances, man selects his clothing so as to keep the tempera- 

 ture of most of the body surface at about 30 C. If the customary activ- 

 ities of the individual involve a heat production which is too great to be 

 dissipated with maintenance of surface temperature at 30, the individual 

 may, and generally does, diminish his food consumption but only at the 

 cost of loss of body substance or ability to do work. Thus Ranke, in 

 the experiment above referred to, found that, of free choice, he 

 would have consumed 400 calories less per day during the summer but 

 that he then lost weight which, for the purpose of the experiment, was to 

 be kept constant. He accordingly ate enough to maintain his body weight 

 but experienced increasing discomfort until, at the end of the month, 

 there was a definite gastro-intestinal disturbance and, apparently, an 

 increased susceptibility to infection. It is important to remember, in this 

 connection, that the average temperature of the room in which Ranke spent 

 most of his time was 21.9 C. in summer and 18.9 C. in winter. The 

 humidity is not stated but was probably lower in winter than in summer, 

 so that the cooling effect of the air was greater in winter than in summer. 

 Moreover, when indoors, Ranke wore the same clothing in summer as in 

 winter, so that it seems quite likely that the dissipation of heat was inter- 

 fered with and that this led to the disturbances he noted. 



If external conditions, such as temperature and humidity, do not 

 permit the removal of the heat produced in ordinary metabolism, the 

 temperature of the body is raised, the basal metabolism is raised and may 

 thus be even greater in warm weather than in moderate (Young). 



It is quite possible that the inability to maintain a high metabolism 

 in warm weather and in the tropics is responsible for the indolence and 

 lack of energy displayed by man under those conditions. 



With very low external temperatures, on the other hand, the heat pro- 

 duced in metabolism may not be sufficient to cover the heat loss, even 

 though this be reduced to a minimum by means of much clothing. The 

 feeling of cold is experienced and muscular activity is increased (shiver- 

 ing), with consequent increase in the production of heat. With short 

 periods of exposure, shivering may not appear and, in such cases, as 

 found by Eijkman(d) (1897), metabolism is the same at from to 12 

 C. as at 24.5 C. though the clothing be light and the subjects complain 

 of cold at the lower temperature. There may be some direct stimulating 

 effect of cold upon metabolism (see discussion in Tigerstedt(Ti), 1919, Vol. 

 I, page 168), but such action must, ordinarily, play a very inconsiderable 

 part. 



