234 THE PHENOMENA OF MOTION 



stituents of plants which, during the day, possessed 

 the power of separating oxygen from chemical com- 

 binations, and of resisting its action, lose this power 

 completely. 



A precisely similar phenomenon is observed in 

 animals. 



The living animal body exhibits its peculiar mani- 

 festations of vitality only at certain temperatures. 

 When exposed to a certain degree of cold, these 

 vital phenomena entirely cease. 



The abstraction of heat must, therefore, be viewed 

 as quite equivalent to a diminution of the vital 

 energy ; the resistance opposed by the vital force to 

 external causes of disturbance must diminish, in 

 certain temperatures, in the same ratio in which the 

 tendency of the elements of the body to combine 

 with the oxygen of the air increases. 



By the combination of oxygen with the consti- 

 tuents of the metamorphosed tissues, the tempera- 

 ture necessary to the manifestations of vitality is 

 produced in the carnivora. In the herbivora, again, 

 a certain amount of heat is developed by means of 

 those elements of their non-azotised food which 

 have the property of combining with oxygen. 



It is obvious that the temperature of an animal 

 body cannot change, if the amount of inspired oxy- 

 gen increases in the same ratio as the loss of heat 

 by external cooling. 



Two individuals, carnivora, of equal weight, ex- 

 posed to unequal degrees of cold, lose, in a given 



