246 ANIMAL HEAT. 



as well as of cold, without injury to health. His power 

 of adaptation is sufficient for the maintenance of a uniform 

 temperature in a range of upwards of 200 Fahrenheit ; a 

 power which is only shared by some of the domestic 

 animals who are his companions in his various abodes. 



Sources and Mode of Production of Heat in the Body. 



To explain the production of heat in the body, several 

 theories have been advanced ; but it now appears certain 

 that the correct one is that which refers the generation of 

 heat, primarily and in general, to certain chemical pro- 

 cesses going on in the system ; but admits, at the same 

 time, that as these chemical changes are carried on in 

 parts whose functions are, to a certain extent, under the 

 influence of the nervous system, therefore the production 

 of heat is liable to be modified, either locally or in every 

 part, by the operation of that system. 



In explaining the chemical changes effected in the 

 process of respiration (p. 230), it was stated that the 

 oxygen of the atmosphere taken into the blood is, most 

 probably, combined, in the course of the circulation, and 

 mainly in the systemic capillary vessels, with the carbon 

 and the hydrogen of disintegrated and absorbed tissues, 

 and of certain elements of food which have not been con- 

 verted into tissues. That such a combination between 

 the oxygen of the atmosphere and the carbon and hydro- 

 gen in the blood, is continually taking place, is made 

 nearly 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 evaporated in the form of car- 

 bonic acid and water. In other words, the blood of warm- 



