214 THE PHENOMENA OF MOTION 



force, is employed to furnish resistance) also in- 

 creases. 



The plant increases in mass until the vital force 

 inherent in it comes into equilibrium with all the 

 other causes opposed to its manifestation. From 

 this period, every new cause of disturbance, added 

 to those previously existing (a change of tempera- 

 ture, for example), deprives it of the power of offer- 

 ing resistance, and it dies down. 



In perennial plants (in trees, for example), the 

 mass of the easily decomposable (azotised) com- 

 pounds, compared with that of the non-azotised, is 

 so small, that of the whole sum of force, only a mi- 

 nimum is expended as resistance. In animals, this 

 proportion is reversed. 



During every period of the life of a plant, the 

 available vital force (that which is not neutralized 

 by resistance) is expended only in one form of vital 

 manifestation, that of growth or increase of mass, 

 or the overcoming of resistance. No part of this 

 force is applied to other purposes. 



In the animal organism, the vital force exhibits 

 itself, as in the plant, in the form of the capacity of 

 growth, and as the means of resistance to external 

 agencies ; but both of these manifestations are con- 

 fined within certain limits. 



We observe in animals, that the conversion of 

 food into blood, and the contact of the blood with 

 the living tissues, are determined by a mechanical 

 force, whose manifestation proceeds from distinct 



