IN THE ANIMAL ORGANISM. 233 



11. 



In the living plant, the intensity of the vital force 

 far exceeds that of the chemical action of oxygen. 



We know, with the utmost certainty, that, by 

 the influence of the vital force, oxygen is separated 

 from elements to which it has the strongest affinity ; 

 that it is given out in the gaseous form, without 

 exerting the slightest action on the juices of the 

 plant. 



How powerful, indeed, must the resistance ap- 

 pear which the vital force supplies to leaves charged 

 with oil of turpentine or tannic acid, when we con- 

 sider the affinity of oxygen for these compounds ! 



This intensity of action or of resistance the plant 

 obtains by means of the sun's light ; the effect of 

 which in chemical actions may be, and is, com- 

 pared to that of a very high temperature (a mode- 

 rate red heat). 



During the night an opposite process goes on in 

 the plant ; w^e see then that the constituents of the 

 leaves and green parts combine with the oxygen of 

 the air, a pro2)erty which in daylight they did not 

 possess. 



From these facts we can draw no other conclu- 

 sion but this : that the intensity of the vital force 

 diminishes with the abstraction of light ; that with 

 the approach of night a state of equilibrium is esta- 

 blished, and that in complete darkness all those con- 



