444 NUTRITION ANIMAL HEAT AND FORCE. 



a time will come when some of the organs necessary to life will be unable to 

 perform their office. When this occurs, there is death from old age, or physio- 

 logical dissolution. This may be a gradual failure of the general process of 

 nutrition or it may occur in some one organ or system that is essential to 

 life. 



ANIMAL HEAT AND FORCE. 



The processes of nutrition in animals are always attended with the devel- 

 opment and maintenance of a bodily temperature that is more or less inde- 

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

 highest animal organizations ; and analogous phenomena have been observed 

 in plants. In cold-blooded animals, nutrition may be suspended by a dimin- 

 ished external temperature, and certain of the functions 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 stupor, called hibernation ; but in man and most 

 of the warm-blooded animals, the general temperature of the body can un- 

 dergo but slight variations. The animal heat is nearly the same in cold and 

 in hot climates ; and if from any cause the body become incapable of keep- 

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

 exposed to heat, death is the inevitable result. 



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

 quantities of heat, it is necessary to fix upon 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 1 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). This force 

 is called a foot-pound. 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 which 

 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 " t \'l 

 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 ex- 

 pressed 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 parantheses. 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 C., will be designated as a 

 kilo.-degree C. 



One pound-degree = 0-252 kilo.-degree C. One kilo.-degree C. = 3'96 

 (nearly 4) pound-degrees. A kilogrammetre represents the force required to 

 raise a weight of one kilogramme one metre. One foot-pound = 0-138 kilo- 

 grammetre. One kilogrammetre = 7'24 foot-pounds. One pound-degree = 

 772 foot-pounds. One pound-degree = 106-6 kilogrammetres. One kilo.- 



