PRODUCTION OF HEAT. 247 



blooded animals appears to be always receiving from the 

 digestive canal and the lungs more carbon, hydrogen, and 

 oxygen than are consumed in the repair of the tissues, 

 and to be always emitting carbonic acid and water, for 

 which there is no other known source than the combination 

 of these elements. By such combination, heat must be 

 continually produced in the animal body. The same 

 amount of heat will be evolved in the union of any given 

 quantities of carbon and oxygen, and of hydrogen and 

 oxygen, whether the combination be rapid and evident, as 

 in ordinary combustion, or slow and imperceptible, as in 

 the changes which are believed to occur in the living body. 

 And since the heat thus arising will be generated wher- 

 ever the blood is carried, every part of the body will be 

 heated equally, or nearly so. 



To establish this theory, it needs to be shown that the 

 quantity of carbon and hydrogen which, in a given time, 

 unites in the body with oxygen, is sufficient to account for 

 the amount of heat generated in the animal within the 

 same time : an amount capable of maintaining the tem- 

 perature of the body at from 98 to 100, notwithstanding 

 a large loss by radiation and evaporation.* 



An attempt to determine this point was made by Dulong 

 and Despretz. Dulong introduced different mammiferous 

 animals, carnivorous as well as herbivorous, into a receiver, 

 in which the changes produced in the air by respiration, 

 and the volume of the different products, could be deter- 

 mined at the same time that the amount of heat lost by 

 the animal could be ascertained. His experiments led him 

 to conclude, among other points, that supposing all the 



* Some heat will also be generated in the combination of sulphur and 

 phosphorus with oxygen, to which reference has been made (p. 226) ; 

 but the amount thus produced has not been estimated, and need not be 

 considered in the exposition of a theory which can, at present, be stated 

 in only the most general terms. 



