236 THE PHENOMENA OF MOTION 



there be a full supply of food and free access of 

 oxygen, the change of matter must be accelerated ; 

 and, along with the augmented transformation, in a 

 given time, of living tissues, a greater amount of 

 vital force must be rendered available for mecha- 

 nical purposes. 



With the external cooling, the respiratory mo- 

 tions become stronger ; in a lower temperature more 

 oxygen is conveyed to the blood ; the waste of 

 matter increases, and if the supply be not kept in 

 equilibrium with this waste, by means of food, the 

 temperature of the body gradually sinks. 



But, in a given time, an unlimited supply of 

 oxygen cannot be introduced into the body ; only a 

 certain amount of living tissue can lose the state of 

 life, and only a limited amount of vital force can be 

 manifested in mechanical phenomena. It is only, 

 therefore, when the cooling, the generation of force, 

 and the absorption of oxygen are in equilibrium 

 together, that the temperature of the body can re- 

 main unchanged. If the loss of heat by cooling go 

 beyond a certain point, the vital phenomena dimi- 

 nish in the same ratio ; for the temperature falls, 

 and the temperature must be considered as a uni- 

 form condition of their manifestation. 



Now experience teaches, that when the temj^era- 

 ture of the body sinks, the power of the limbs to 

 produce mechanical effects (or the force necessary 

 to the voluntary motions) is also diminished. The 

 condition of sleep ensues, and at last even the invo- 



