ANIMAL HEAT. 



23 



chemical action which takes place in them. The temperature 

 of an organ necessarily results from the heat supplied to it 

 by the blood, from that which has been produced in its 

 interior, and from that which it has lost. Thus it is that 

 certain veins, those of the limbs, for example, bring back 

 blood colder than that of the corresponding arteries ; whilst 

 others, like the sub-hepatic veins which leave the liver, bring 

 back blood warmer than that which has entered the hepatic 

 gland. In fact, after all compensations are made, the heated 

 venous blood predominates in the living organism over the 

 cooled blood ; so that it re-enters the heart 1 warmer than 

 wheu it came out of it. ^ 



This leads us to study the question of the temperature of 

 animals. 



Among the different animal species, some, while producing 

 heat, are subject to the variations of the surrounding tem- 

 perature, so that they have been called cold blooded. They are 

 now called animals of variable temperature, which is more 

 exact. As for the animals called warm blooded, they possess 

 the singular property of having the blood in the deeper 

 portions of their bodies almost always at the same tempera- 

 ture, notwithstanding the variations of the external heat. 

 Thus, a man, sailing from the polar regions to the equator, 

 may be subject, in a few weeks, to changes of 30^ in the 

 surrounding temperature, but his blood remains at about 

 38°. 



It is easy to understand that in the midst of incessant 

 variations in the production of heat inside the organism, 

 and of the no less great variations in the causes of its 

 waste, such uniformity can only be obtained by means of a 

 regulator of the temperature. We shall now proceed to certain 

 developments of the wonderful functions of the regulator of 

 the animal temperature. 



Human industry has often found it difficult to provide fixed 

 temperatures, or at least to counterbalance the causes of ex- 

 cessive heat and cold. A hot -house must neither fall below, 

 nor rise above a certain temperature. But this problem is 

 relatively a simple one ; the hot-house is always warmer 

 than the external air ; it can only be subjected to more or less 



