REGULATION OF THE TEMPERATURE. 239 



for the means by which the temperature is regulated ; in 

 other words, by which it is prevented from rising beyond 

 the normal point on the one hand, or sinking below it on 

 the other. The chief indirect means for accomplishing the- 

 same end are, variations in the amount and quality of the 

 food and drink taken, variations in clothing, and in 

 exposure to external heat or cold. 



In order to understand the means by which the heat of 

 the body is regulated, it is necessary to take into consi- 

 deration the following facts : First, the immediate source 

 of heat in the body is the presence of a large quantity of" 

 a warm fluid the blood, the temperature of which is, in 

 health, about 100 F. In the second place, the blood,, 

 while constantly moving in a multitude of different streams, 

 is, every minute or so, gathered up in the heart into one 

 large stream, before being again dispersed to all parts of 

 the body. In this way, the temperature of the blood 

 remains almost exactly the same in all parts ; for while a 

 portion of it in passing through one organ, as the skin, 

 may become cooler, and through another organ, as the 

 liver, may become warmer, the effect on each separate- 

 stream is more or less neutralized when it mingles with 

 another, and an average is struck, so to speak, for all the- 

 streams when they form one, in passing through the 

 heart. 



The means by which the skin is able to act as one of 

 the most important organs for regulating the temperature 

 of the blood, are (l), that it offers a large surface for 

 radiation, conduction, and evaporation ; (2), that it con- 

 tains a large amount of blood ; (3), that the quantity of 

 blood contained in it is the greater under those circum- 

 stances which demand a loss of heat from the body, and 

 vice versa. For the circumstance which directly determines 

 the quantity of blood in the skin, is that which governs 

 the supply of blood to all the tissues and organs of the 

 body, namely, the power of the vaso-motor nerves to cause 



