242 THE PHENOMENA OF MOTION 



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 hyberna- 

 tlon, 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 available for the involuntary mo- 

 tions. 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 be- 

 comes uneatable. The condition 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 de- 

 stroyed. 



But however closely the conditions of the produc- 

 tion of heat and of force may seem to be connected 

 together, with reference to mechanical effects, yet 

 the disengagement of heat can in no way be consi- 

 dered as in itself the only cause of these effects. 



All experience proves, that there is, in the organ- 

 ism, only one source of mechanical power ; and this 



