238 THE PHENOMENA OF MOTION 



take into consideration the time during which the 

 force is manifested, it is obvious that the amount of 

 force develoj)ed by the horse is far greater than in 

 the case of the whale. 



In climbing high mountains, where, in conse- 

 quence of the respiration of a highly rarefied atmo- 

 sphere, much less oxygen is conveyed to the blood, 

 in equal times, than in valleys or at the level of the 

 sea, the change of matter diminishes in the same 

 ratio, and with it the amount of force available for 

 mechanical purposes. For the most part, drow^siness 

 and want of force for mechanical exertions come 

 on ; after twenty or thirty steps, fatigue compels us 

 to a fresh accumulation of force by means of rest 

 (absorption of oxygen without waste of force in 

 voluntary motions). 



By the absorption of oxygen into the substance 

 of living tissues, these lose their condition of life, 

 and are separated as lifeless, unorganised com- 

 pounds ; but the whole of the inspired oxygen is not 

 applied to these transformations: the greater part 

 serves to convert into gas and vapour all matters 

 which no longer belong to the organism ; and, as 

 formerly mentioned, the combination of the ele- 

 ments of such compounds with the oxygen produces 

 the temperature proper to the animal organism. 



The production of heat and the change of matter 

 are closely related to each other ; but although heat 

 can be produced in the body without any change of 

 matter in living tissues, yet the change of matter 



