ii THE THERMIC ECONOMY OF THE ORGANISM 77 



parts, the viscera and muscles, the chief thermogenic organs ; when, 

 on the other hand, the peripheral vessels dilate, the quantity of 

 blood circulating in the inner parts is decreased. In the former 

 case the total production of heat due to the metabolism of the 

 viscera and the muscular system must increase, while in the latter 

 it is diminished. We therefore see that the vasomotor system 

 contributes in two ways to the maintenance of a uniform body 

 temperature : by regulating the loss of heat in the periphery, and 

 the regulation of its production in the inner tissues. The latter 

 fact demands a more detailed analysis. 



Numerous experiments have proved that the processes of 

 oxidation in the organism increase, within certain well - defined 

 limits, when the outer temperature goes down, and diminish when 

 it rises. Amongst well-known researches upon this subject we 

 may mention those made on the guinea-pig by Pfliiger's pupils, 

 on the cat by Duke Carl Theodore of Bavaria, and on man by 

 Pettenkofer, Voit, and Fredericq. 



Colasanti and Ditmar Finkler, who made experiments on 

 guinea - pigs under Pfliiger's direction, found that when these 

 animals were exposed to a temperature which was gradually 

 raised from 3 to 21, they consumed a steadily decreasing 

 quantity of oxygen per hour and per kgrm. of their weight. 

 Duke Carl Theodore of Bavaria observed that the carbon dioxide 

 discharged by the cat steadily decreased as the outer temperature 

 was raised from - 5 -5 to + 30-8. Pettenkofer and Voit proved, 

 in the case of a young man weighing 71 kgrms., the gradual 

 decrease in the quantity of carbon dioxide and nitrogen discharged 

 when the temperature of the environment was raised from 4*4 to 

 30. Fredericq (1882), experimenting on himself, found that in 

 the morning in a fasting condition, and at a temperature of 

 15-20, he absorbed 4 to 5 litres of oxygen in fifteen minutes. 

 When, however, he exposed himself naked to a temperature of 10, 

 the oxygen absorbed in the same length of time increased to 5 '5 

 and even to 6 litres. 



From this and other researches made by various investigators, 

 we may draw the general conclusion that the organic combustion, 

 on which the production of heat depends, increases or decreases 

 according as the outer temperature falls or rises within certain 

 limits, which vary according to the animals experimented upon. 

 Homoio thermic animals therefore possess a mechanism regulating 

 the production of heat, which, in conjunction with the mechanism 

 regulating the loss of heat, tends to preserve the equilibrium of the 

 thermic balance. 



We must now define more accurately the limits of the 

 efficiency of the regulation of the production of heat, and 

 determine how it serves to protect us from either cold or heat. 



In the first place it is necessary to remember that cold does 



