IN THE LAST HALF-CENTUEY. 127 



assumption that the physical and chemi- 

 cal processes which take place in the living 

 body are of the same order as those which 

 take place out of it ; and that whatever 

 energy is exerted in producing such phe- 

 nomena is derived from the common stock 

 of energy in the universe. In the fifth 

 place, modern physiology investigates the 

 relation between physical and psychical 

 phenomena, on the assumption that mo- 

 lecular changes in definite portions of 

 nervous matter stand in the relation of 

 necessary antecedents to definite mental 

 states and operations. The work which 

 has been done in each of the directions 

 here indicated is vast, and the accumula- 

 tion of solid knowledge, which has been 

 effected, is correspondingly great. For the 

 first time in the history of science, physi- 

 ologists are now in the position to say 

 that they have arrived at clear and dis- 

 tinct, though by no means complete, con- 

 ceptions of the manner in which the great 



