258 ANIMAL HEAT. 



that of carbonic acid produced, will be equal in the two cases. In 

 one instance we have a rapid combustion, in the other a slow com- 

 bustion ; the total effect being the same in both. 



Such is the mode in which heat is commonly produced by artifi- 

 cial means, its evolution is here dependent upon two principal 

 conditions, which are essential to it, and by which it is always 

 accompanied, viz., the consumption of oxygen, and the production 

 of carbonic acid. 



Now, since the two phenomena just mentioned are presented 

 also by the living body, and since they are accompanied here, too, 

 by the production of animal heat, it was very natural to suppose 

 that in the animal organization, as well as elsewhere, the internal 

 heat must be owing to an oxidation or combustion of carbon. Ac- 

 cording to Lavoisier, the oxygen taken into the lungs was sup- 

 posed to combine immediately with the carbon of the pulmonary 

 tissues and fluids, producing carbonic acid, and to be at once re- 

 turned under that form to the atmosphere ; the same quantity of 

 heat resulting from the above process as would have been produced 

 by the oxidation of a similar quantity of carbon in wood or coal. 

 Accordingly, he regarded the lungs as a sort of stove or furnace, 

 by which the rest of the body was warmed, through the medium of 

 the circulating blood. 



It was soon found, however, that this view was altogether erro- 

 neous ; for the slightest examination shows that the lungs are not 

 perceptibly warmer than the rest of the body ; and that the heat- 

 producing power, whatever it may be, does not reside exclusively 

 in the pulmonary tissue. Furthermore, subsequent investigations 

 showed the following very important facts, which we have already 

 mentioned, viz., that the carbonic acid is not formed in the lungs, 

 but exists in the blood before its arrival in the pulmonary capilla- 

 ries ; and that the oxygen of the inspired air, so far from combining 

 with carbon in the lungs, is taken up in solution by the blood- 

 globules, and carried away by the current of the general circulation. 

 It is evident, therefore, that this oxidation or combustion of the 

 blood must take place, if at all, not in the lungs, but in the capil- 

 laries of the various organs and tissues of the body. 



Liebig accordingly adopted Lavoisier's theory of the production 

 of animal heat, with the above modification. He believed the heat 

 of the animal body to be produced by the oxidation or combustion 

 of certain elements of the food while still circulating in the blood ; 

 these substances being converted into carbonic acid and water by 



