442 KEGULATION OF THE TEMPERATURE. 



C. Ludwig and Sanders-Ezn found, that in a rabbit there was a rapid increase in 

 the amount of C0 2 given off, when the surroundings were cooled from 38 to 6-7C. , 

 while the excretion was diminished when the surrounding temperature was raised 

 from 4-9 to 35-37, so that the thermal stimulation, due to the temperature of 

 the surrounding medium, acted upon the combustion within the body. Pfliiger 

 found that a rabbit which was dipped in cold water used more and excreted 

 more C0 2 . 



If the cooling action was so great as to reduce the bodily temperature to 30, the 

 exchange of gases diminished, and where the temperature fell to 20, the exchange 

 of gases was diminished one-half. It is to be remembered, however, that the 

 excretion of C0 2 does not go hand in hand with the formation of C0 2 , so that the 

 increased excretion of C0 2 in a cold bath is perhaps due to more complete expira- 

 tion, and Berthelot has proved that the formation of C0 2 is not a certain test of 

 the amount of heat produced. If mammals be placed in a warm bath, which is 

 2-3 higher than their own temperature, the excretion of C0 2 and the consump- 

 tion of are increased, owing to the stimulation of their metabolism (Pfliiger), 

 while the excretion of urea is also increased in animals (Naunyn) and in man 

 (Schleich). 



(3.) Cold acting upon the skin causes involuntary muscular move- 

 ments (shivering, rigors), and also voluntary movements, both of which 

 produce heat. 



The cold excites the action of the muscles, which is connected with processes of 

 oxidation (Pfluger). After poisoning with curara, which paralyses voluntary 

 motion, this regulation of the heat falls to a minimum (Rb'hrig and Zuntz). 



(4.) Variations in the temperature of the surroundings affect the 

 appetite for food; in winter, and in cold regions, the sensation of 

 hunger and the appetite for the fats, or such substances as yield much 

 heat when they are oxidised, are increased ; in summer, and in hot 

 climates, they are diminished. Thus the mean temperature of the 

 surroundings, to a certain extent, determines the amount of the heat- 

 producing substances to be taken in the food. In winter the amount 

 of ozone in the air is greater, and thus the oxidising power of the 

 inspired air is increased. 



II. Regulatory mechanisms governing the excretion of heat. 

 The mean amount of heat given off by the human skin in 24 hours, 

 by a man weighing 82 kilos, is 2,092-2,592 calories i.e., 1-3G-1-60 

 per minute. 



(1.) Increased temperature causes dilatation of the cutaneous vessels; 

 the skin becomes red and congested, soft, and with more fluids, so that 

 it becomes a better conductor of heat; the epithelium is moistened, and 

 sweat appears upon the surface. Thus increased excretion of heat 

 is provided for, while the evaporation of the sweat also abstracts heat. 



Cold causes contraction of the cutaneous vessels ; the skin becomes 

 pale, less soft, poorer in juices, and collapsed; the epithelium becomes 

 dry, and does not permit fluids to pass through it to be evaporated, so 

 that the excretion of heat is diminished. The excretion of heat from 



