512 PHYSIOLOGY. 



tion is almost proportionately increased. So nearly are the genera- 

 tion and loss balanced that during actual work there is registered 

 but a rise of a degree and a fraction. With the conclusion of the 

 muscular activity the temperature very rapidly falls to normal. 

 Mental work causes a rise of both the general as well as local tem- 

 perature of the brain and head. The increase registered is usually 

 about 0.1 C. 



Food causes a very slight rise in temperature; sleep, in itself, 

 has no effect. Inactivity is a very marked factor in producing a fall. 

 As inaction is very prominent during sleep, the latter has been 

 erroneously given the credit for causing the drop in temperature. 

 Lying perfectly quiet will produce identical results. Because of the 

 heat, the inhabitants of tropical countries possess a slightly higher 

 temperature. The difference is less than 1 C. 



Extremes of Temperature. During excessively hot spells in 

 summertime when the temperature of the enveloping atmosphere is 

 considerably above that of the normal body-temperature, it is remark- 

 able to find that the temperature of the body has not been raised one 

 degree. This result is mainly accomplished by reason of the heat 

 extracted from the body's surface during evaporation. 



The limit of extreme cold is reached when the lymph within the 

 animal's tissues is frozen. Fishes have been incased within ice and 

 then found completely recovered upon being thawed out and placed 

 in a warmer medium. Normally, the range of temperature in a man 

 is about 1 C. However, drunkards have been known, after exposure 

 to extreme cold, to have a bodily temperature as low as 24 C. with, 

 out fatality. 



Cases of temperature as high as 45 C. have been noted and yet 

 recovery has taken place. Experimentally, Bernard found that, 

 when the internal temperature of rabbits was raised to 45 C., they 

 died. According to his view, death occurred as the result of stop- 

 page of the heart from the hot, circulating blood, causing rigor 

 mortis of the musculature of this organ. 



Temperature of the Blood, The average temperature of the 

 blood is 39 C., but there are found numerous variations in different 

 regions. The blood of the superficial veins is cooler than that of 

 the internal veins, due to prolonged exposure while traversing the 

 course of the former. The warmest blood of the body is that of the 

 hepatic veins. The blood in the veins is cooler than the blood in the 

 corresponding arteries, due to the more superficial position of the 

 former. The temperature of the blood of the left heart is some- 



