OF TILE PHYSICAL CAUSE OF ANIMAL IIEAT, With regard to the physical eau of animal heat, or to its mode of production, there was a time, which we have not yet left very far behind us, when natural philosophers and chemists imagined they possessed the secret, especially with reference to the mineral king dom. They have now discovered their mis take; and as the evolution of heat is a mystery to them, it is not to be expected that it is less so to physiologists, as manifested in the do main which they cultivate in peculiar. The problem, in fact, becomes immensely com plicated by a variety of phenomena when from the inorganic we ascend to the organic world. All that could be done has been accomplished ; from the particular conditions of organization and of function upon which this effect seemed to depend, physiologists have risen to those that were the most general and com prehensive. This, in fact, was the end we proposed in commencing this article. That nothing may be omitted which can make the sketch inure complete, and none of the great inquiries which have had animal heat for their object may be passed over in silence, we shall briefly cite the more important of those in which the mode of production of animal heat is discussed, always reserving to ourselves the opportunity of treating several of these more fully in our article on RESP I RATION.
Lavoisier, from his labours on combustion, which laid the foundation of the chemical doctrines of the age that has just elapsed, conceived the ingenious idea of explaining the phenomena of animal heat by the combustion of the carbon and hydrogen of the blood by the oxygen of the air in the process of respi ration, and the experiments which he instituted upon this point along with the illustrious La I'lace appeared to confirm his idea. Still it
was found impossible to give an account of the production of the whole heat engendered by animals. All that Lavoisier and La Place in ferred was, that the heat evolved by an animal was almost entirely produced by the combus tion which occurs in respiration. As the calo rific power was measured in one animal, and the consumption of oxygen in another, it is evident that the inference, vitiated in its ele ments, became nnich less precise than it would otherwise have been.
This consideration as well as others induced 111. Dulong, who is as well versed in mecha nical philosophy as in chemistry, to take up this subject again. After numerous experi ments, conducted with every precaution that could secure accuracy of result, he found that the heat disengaged by the fixation of the oxygen in the act of respiration was not equal to the whole of that which was produced by an animal. This inquiry (which however stood in no need of confirmation) has been con firmed by the analogous inquiries of M. De sprctz, who arrived at the same numerical results. The hypothesis in question, there fore, gives no solution of the problem.