404 THE POPULAR SCIENCE MONTHLY. 



the chest heaves, is composed of very various substances. It con- 

 tains mineral salts, such as chlorures, sulphates, phosphates of potas- 

 sium, soda, lime, magnesia, coloring-matters, fatty particles, neutral 

 substances of the nature of starch, and nitrogenized products, such as 

 albumen and fibrin. The salts undergo slight changes in the torrent 

 of circulation ; they are eliminated by the chief emunctories. The 

 neutral matters of the nature of starch are converted into glycogene 

 and fat. The fatty particles undergo in the blood only such oxidiza- 

 tions as produce certain derivatives of the same order. And, last, 

 the nitrogenized products are made over into fibrin, musculin, ossein, 

 pepsin, pancreatin, compounds all differing very slightly. It is the first 

 portion of the chemical process which is effected in the principal fluid 

 of the body. All these materials, elaborated at different points of the 

 circulating current, and designed to be assimilated, are destroyed in 

 the very organs in which they had been fixed. The glycogene is trans- 

 formed into sugar, which is burned, yielding water and carbonic acid ; 

 the fatty acids are partly eliminated by the skin, and partly burned. 

 As to the plastic matters which form the web of the tissues, we know 

 little about the chemical relation which connects these with their prod- 

 ucts of destruction urea, creatine, cholesterine, uric acid, and xan- 

 thine. Such is a rapid sketch of the principal chemical phenomena 

 which, taking place throughout the entire system, kindle everywhere an 

 evolution of more or less intense heat. There is no central organ, then, 

 for feeding the vital fire every anatomical element performs its share; 

 and, if a nearly uniform temperature exists throughout the body, it is be- 

 cause the blood diffuses heat regularly into the various parts it bathes. 

 Now, how can the amount of heat to which these reactions may 

 give rise be ascertained? Lavoisier arrived at it in a very simple 

 manner. After comparing the oxygen absorbed by the animal with 

 the carbonic acid and watery vapor thrown off, he deduced the weight 

 of the carbon and hydrogen burned, by assuming that the formation 

 of carbonic acid and of water produces in the system the same amount 

 of heat that it would produce if taking place by means of free carbon 

 and hydrogen. This is very nearly the result he obtained : A man 

 weighing 132 pounds burns in 24 hours, at the average temperature 

 of Paris, very nearly 11 ounces of carbon, and \\ of an ounce of hy- 

 drogen, and thus develops 3,297 heat units. During the same period 

 he loses through his lungs and skin 2f pounds of watery vapor, which 

 take from him 697 heat-units. There remain, then, nearly 2,600 heat- 

 units to account for. Other analogous estimates have been made, and 

 physiologists have deduced from them the conclusion that a man of 

 average weight produces in our climate 3,250 heat-units every day ; 

 that is to say, a sufficient amount of heat to raise seven gallons of 

 water to the boiling-point. These figures, though approximations, 

 give a sufficiently clear notion of the power of the animal economy to 

 generate heat. 



