REGULATION OF THE BODY'S TEMPERATURE 407 



time being exposed to greater or less variations in the temperature of the 

 surrounding medium, neither the thickness of the clothing nor that of the 

 adipose tissue is being changed to correspond with these variations; and yet 

 the body maintains its temperature unchanged. The sum total of all those 

 processes by which this constancy is maintained is comprehended under the 

 term heat regulation of the body. These processes can be divided into two 

 groups according as they relate to heat production or to heat loss. 



The way in which the production of heat varies under the influence of the 

 surrounding temperature has been already presented in Chapter IV (page 

 114). But heat production is influenced also by the amount of food, and in 

 controlling the latter we have a means of adapting the transformation of 

 substance in the body to the requirements of heat regulation. 



A noteworthy illustration is given by K. E. Ranke, who studied his diet 

 both in Germany and during a scientific expedition to Brazil. Allowing him- 

 self free choice of food, the amount being controlled only by his appetite, his 

 total intake between the temperatures of 15 and 22 C. was on the average 

 3,300-3,500 Cal. In a dry climate at a temperature of 25 C., it fell to 2,800 Cal., 

 and at an atmospheric temperature of 25-28 with a humidity of about eighty- 

 three per cent, it reached the low level of 1,970 Cal. (26.9 Cal. per kg. body 

 weight). His body weight decreased however on this low ration. In order to 

 recover his original weight he was obliged to adopt a richer diet, but various 

 disturbances in his general health appeared while he was experimenting in this 

 direction. 



A. REGULATION OF HEAT LOSS 



As we have seen above the temperature of the skin depends primarily upon 

 the blood supply; the greater the amount of blood flowing through it, the 

 warmer it becomes. But the warmer the skin becomes, other conditions being 

 the same, the greater is the loss of heat from the skin by radiation and con- 

 duction. The heat loss by radiation and conduction therefore depends upon 

 the amount of blood supplied to the skin. 



The blood vessels of the skin, like the other vessels of the body, are under 

 the influence of the vasomotor mechanisms, and are constricted or dilated 

 according to the momentary requirements of the heat regulation. Thus in 

 cold weather and when the production of heat in the body is not greatly 

 increased by muscular work, they are constricted; and in hot weather they 

 are dilated. 



These changes in the blood supply of the skin serve in another, and per- 

 haps still more important manner, to regulate the loss of heat. During its 

 flow through the cutaneous vessels, the blood naturally gives off heat, and 

 returns to the interior somewhat cooled. When the vessels are dilated, more 

 blood flows through them, and more heat is thus lost than when they are 

 constricted and the quantity of blood flowing through them is small. While 

 the cutaneous vessels are constricted, the vessels of the abdominal viscera and, 

 as it appears from the investigations of Wertheimer, those also of the muscles 

 i. e., of the most important heat-producing organs are dilated; while dur- 

 ing dilatation of the cutaneous vessels, those of the abdominal viscera are 

 constricted. 



