IN THE ANIMAL ORGANISM. 221 



We know not how a certain something, invisible and 

 imponderable in itself (heat), gives to certain bodies 

 the power of exerting an enormous pressure on sur- 

 rounding objects ; we know not even how this some- 

 thing itself is produced when we burn wood or coals. 



So is it with the vital force, and with the phenomena 

 exhibited by living bodies. The cause of these phe- 

 nomena is not chemical force ; it is not electricity, nor 

 magnetism ; it is a force which has certain properties in 

 common with all causes of motion and of change in form 

 and structure in material substances. It is a peculiar 

 force, because it exhibits manifestations which are found 

 in no other known force. 



.'.;-.: ii. , 



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 appear, 

 which the vital force supplies to leaves charged with 

 oil of turpentine or tannic acid, when we consider the 

 affinity of oxygen for these compounds ! 

 19* 



