ANIMAL HEAT AND FORCE 395 



ANIMAL HEAT AND FORCE 



The processes of nutrition in animals are attended with the develop- 

 ment and maintenance of a body-temperature that is more or less inde- 

 pendent of external conditions. This is true in the lowest as well as 

 the highest animal organisms ; and analogous phenomena have been 

 observed in plants. In cold-blooded animals nutrition may be sus- 

 pended by a diminished external temperature, and certain of the func- 

 tions become temporarily arrested, to be resumed when the animal is 

 exposed to a greater heat. This is true, to some extent, in certain warm- 

 blooded animals that periodically pass into a condition of torpor, called 

 hibernation ; but in man and most of the warm-blooded animals, the 

 general temperature of the body undergoes but slight variations. Cer- 

 tain animals pass into a condition analogous to hibernation under the 

 influence of the intense heat of summer in tropical countries. This 

 condition is called estivation. It has been observed in the tenrec of 

 Madagascar a kind of hedgehog to continue for three months dur- 

 ing the hot season. The animal heat is nearly the same in cold and 

 in hot climates ; and if from any cause the body becomes incapable of 

 keeping up its temperature when exposed to cold, or of moderating it 

 when exposed to heat, death is the result. 



Estimated Quantity of Heat produced by the Body. In order to 

 express quantities of heat, it is necessary to fix on some definite quantity 

 to be taken as a heat-unit. In what is to follow, a heat-unit is to be 

 understood as the heat required to raise the temperature of one pound 

 of water one degree from 32 Fahr. (pound-degree Fahr.). 



It has been calculated that one heat-unit is equal to the force 

 expended in raising one pound 772 feet or 772 pounds one foot (Joule). 

 The equivalent of heat in force has been calculated by estimating the 

 heat produced by a certain weight falling through a certain distance, 

 assuming the falling force to be precisely equal to the force that has 

 been used in raising the weight ; but physicists have not actually suc- 

 ceeded in so completely converting heat into force as to raise one pound 

 772 feet or 772 pounds one foot, by the expenditure of one heat-unit. 



The heat-unit and its equivalent in force are, of course, differently 

 expressed according to the metric system. When heat-units or foot- 

 pounds are given in the text, the equivalents, according to the metric 

 system, are given in parentheses. These equivalents are as follows : 



A heat-unit, according to the metric system, or the heat required to 

 raise the temperature of one kilo of water one degree from zero C, will 

 be designated as a kilo-degree C. A kilo-degree is called a large calorie. 

 A gram-degree the heat required to raise the temperature of one 



