AND ANIMAL LIFE. 397 



an exciting or depressing tendency ; or, in other 

 Words, exhibit a superabundance or deficiency of 

 vital energy according to the quantity of oxygen 

 which the sanguineous fluid contains. From this 

 reasoning we are not to conclude that vitality 

 and oxygen are synonymous ; with as much 

 consistency we might state that a machine and 

 its source of motion are the same. The func- 

 tions of the animal frame are retarded or accele- 

 rated according to the quantity of oxygen ex- 

 isting in the blood, or according to its changes in 

 the lungs ; and we also observe that the diffe- 

 rent machines which man employs, whatever be 

 the power that continues their action, have a 

 jforce proportionate to the extent of the moving cause. 

 But, in these examples, there is no similarity, 

 either in the agent which operates, the materials 

 acted upon, or the effects produced. 



Life is not a simple principle, but is the result of 

 compound principles and actions pervading and 

 common to every part of organized nature. 



