236 AXIMAL HEAT. 



Sources and Mode of Production of Heat in the Body. 



In explaining the chemical changes effected in the pro- 

 cess of respiration (p. 219), it was stated that the oxygen 

 of the atmosphere taken into the blood is combined, in the 

 course of the circulation, with the carbon and the hydrogen 

 of disintegrated and absorbed tissues, and of certain ele- 

 ments of food which have not been converted into tissues. 

 That such a combination between the oxygen of the atmo- 

 sphere and the carbon and hydrogen in the blood, is con- 

 tinually taking place, is made certain by the fact, that a 

 larger amount of carbon and hydrogen is constantly being 

 added to the blood from the food than is required for the 

 ordinary purposes of nutrition, and that a quantity of 

 oxygen is also constantly being absorbed from the air in 

 the lungs, of the disposal of which no account can be given 

 except by regarding it as combining, for the most part, 

 with the excess of carbon and hydrogen, and being excreted 

 in the form of carbonic acid and water. In other words^ 

 the blood of warm-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 com- 

 bination, heat is 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 occur in the living body. And since 

 the heat thus arising will be generated wherever the blood 



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

 phosphorus with oxygen, to which reference has been made (p. 216) ; 

 but the amount thus produced is but small. 



