IN THE ANIMAL ORGANISM. 199 



The phenomena of vitality in a living organism 

 diminish in intensity when heat is abstracted, pro- 

 vided the lost heat be not restored by other causes. 



Deprivation of food soon puts a stop to all mani- 

 festations of vitality. 



The contact of the living tissues with the ele- 

 ments of nutrition is determined in the animal body 

 by a mechanical force produced within the body, 

 which gives to certain organs the power of causing 

 change of place, of producing motion, and of over- 

 coming mechanical resistance. 



We may communicate motion to a body at rest 

 by means of a number of forces, very diiferent in 

 their manifestations. Thus, a time-piece may be 

 set in motion by a falling weight (gravitation), or 

 by a bent spring (elasticity). Every kind of motion 

 may be produced by the electric or magnetic force, 

 as well as by chemical attraction ; while w^e cannot 

 say, as long as we only consider the manifestation of 

 these forces in the phenomenon or result j^roduced, 

 which of these various causes of change of place has 

 set the body in motion. 



In the animal organism we are acquainted with 

 only one cause of motion ; and this is the same 

 cause which determines the growth of living tissues, 

 and gives them the power of resistance to external 

 agencies ; it is the vital force. 



In order to attain a clear conception of these 

 manifestations of the vital force, so different in 

 form, we must bear in mind, that evei-y known 



