230 THE PHENOMENA OF MOTION 



part, although a certain momentum of motion be ex- 

 pended in keeping up the circulation, will not be sep- 

 arated and expelled from the body. 



With the return of the higher temperature, the ca- 

 pacity of growth increases in the same ratio, and the 

 motion of the blood increases with the absorption of 

 oxygen. Many of these animals become emaciated 

 during the winter sleep, others not till after awaking 

 from it. 



In hybernating animals the active force of the living 

 parts is exclusively devoted, during hybernation, to the 

 support of the involuntary motions. The expenditure 

 of force in voluntary motion is entirely suppressed. 



In contradistinction to these phenomena, we know 

 that, in the case of excess of motion and exertion, the 

 active force in living parts may be exclusively and 

 entirely consumed in producing voluntary mechanical 

 effects ; in suchwise that no force shall remain avail- 

 able for the involuntary motions. A stag may be 

 hunted to death ; but this cannot occur without the 

 metamorphosis of all the living parts of its muscular 

 system, and its flesh becomes uneatable. The con- 

 dition of metamorphosis into which it has been brought 

 by an enormous consumption both of force and of 

 oxygen, continues when all phenomena of motion have 

 ceased. In the living tissues, all the resistance offered 

 by the vital force to external agencies of change is 

 entirely destroyed. 



But however closely the conditions of the produc- 



