IV 



VITALITY 



THE origin, growth, and energies of living things are 

 subjects which have always engaged the attention 

 of thinking men. To account for them it was usual 

 to assume a special agent, free to a great extent from the 

 limitations observed among the powers of inorganic nat- 

 ure. This agent was called vital force ; and, under its 

 influence, plants and animals were supposed to collect 

 their materials and to assume determinate forms. Within 

 the last few years, however, our ideas of vital processes 

 have undergone profound modifications; and the interest, 

 and even disquietude, which the change has excited are 

 amply evidenced by the discussions and protests which 

 are now common regarding the phenomena of vitality. 

 In tracing these phenomena through all their modifica- 

 tions, the most advanced philosophers of the present day 

 declare that they ultimately arrive at a single source of 

 power, from which all vital energy is derived; and the 

 disquieting circumstance is that this source is not the di- 

 rect fiat of a supernatural agent, but a reservoir of what, 

 if we do not accept the creed of Zoroaster, must be re- 

 garded as inorganic force. In short, it is considered as 

 proved that all the energy which we derive from plants 

 and animals is drawn from the sun. 



A few years ago, when the sun was affirmed to be the 



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