262 ANIMAL HEAT. 



mass of the blood is not altered. Finally it has been demonstrated 

 by Bernard that in the natural state of the system there is a marked 

 difference in the temperature of the different organs and of the blood 

 returning from them. 1 The method adopted by this experimenter 

 was to introduce, in the living animal, the bulb of a fine thermo- 

 meter successively into the bloodvessels entering and those leaving 

 the various internal organs. The difference of temperature in these 

 two situations showed whether the blood had lost or gained in heat 

 while traversing the capillaries of the organ. Bernard found, in 

 the first place, that the blood in passing through the lungs, so far 

 from increasing, was absolutely diminished in temperature; the 

 blood on the left side of the heart being sometimes a little more 

 and sometimes a little less than one-third of a degree Fahr. lower 

 than on the right side. This slight cooling of the blood in the 

 lungs is owing simply to its exposure to the air through the pul- 

 monary membrane, and to the vaporization of water which takes 

 place in these organs. In the abdominal viscera, on the contrary, 

 the blood is increased in temperature. It is sensibly warmer in the 

 portal vein than in the aorta ; and very considerably warmer in the 

 hepatic vein than in either the portal or the vena cava. The blood 

 of the hepatic vein is in fact warmer than that of any other part 

 of the body. The production of heat, therefore, according to Ber- 

 nard's observations, is more active in the liver than in any other 

 portion of the system. As the chemical processes of nutrition are 

 necessarily different in the different tissues and organs, it is easy to 

 understand why a specific amount of heat should be produced in 

 each of them. A similar fact, it will be recollected, was noticed by 

 Dutrochet, in regard to the different parts of the vegetable organ- 

 ization. 



YI. Animal heat has been supposed to stand in a special relation 

 to the production of carbonic acid, because in warm-blooded animals 

 the respiratory process is more active than in those of a lower 

 temperature; and because, in the same anirrial, an increase or di- 

 minution in the evolution of heat is accompanied by a correspond- 

 ing increase or diminution in the products of respiration. But 

 this is also true of all the other excretory products of the body. An 

 elevation of temperature is accompanied by an increased activity 

 of all the nutritive processes. Not only carbonic acid, but the 



1 Gazette Hebdomadaire, Aug. 29 and Sept. 26, 1856. 



