46 FKAGMESTS OF SCIENCE. 



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 inor- 

 ganic nature. 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 modifica- 

 tions; and the interest, and even disquietude, which 

 the change has excited are amply evidenced by the 

 discussions and protests which are now common, re- 

 garding the phenomena of vitality. In tracing these 

 phenomena through all their modifications, 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 direct fiat of 

 a supernatural agent, but a reservoir of what, if we do 

 not accept the creed of Zoroaster, must be regarded 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 source of life, nine out of ten of those who are 

 alarmed by the form which this assertion has latterly 



