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 different 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 we cannot 

 say, as long as we only consider the manifestation of 

 these forces in the phenomenon or result produced, 

 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 every known 



