210 THE STORY OP LIFE'S MECHANISM. 



application of physical and chemical forces acting 

 in the living machine. These secondary pheno- 

 mena include such processes as the digestion 

 and absorption of food, circulation, respiration, 

 excretion, bodily motion, etc. Nervous phe- 

 nomena also doubtless come under this head, at 

 least so far as concerns nervous force. We have 

 been obliged, however, to exclude from this 

 correlation the mental phenomena. Mental phe- 

 nomena can not as yet be measured, and have 

 not yet been shown to be correlated with physical 

 energy. In other words, it has not yet been 

 proved that mental force is energy at all ; and if 

 it is not energy, then of course it can not be 

 included in the laws which govern the physical 

 energy of the universe. Although a close rela- 

 tion exists between physical changes in the brain 

 cells and mental phenomena, no further connec- 

 tion has yet been drawn between mental power 

 and physical force. All other secondary phe- 

 nomena, however, are intelligently explained by 

 the action of natural forces in the machinery of 

 the living organism. 



While we have thus found that the secondary 

 phenomena of life are intelligible as the result 

 of the structure of the machine, certain other 

 fundamental phenomena have been constantly 

 forcing themselves upon our attention as a founder 

 tion of these secondary activities. The power of 

 contraction, the power of causing certain kinds 

 of chemical change to occur which result in meta- 

 bolism, the property of sensibility, the property 

 of reproduction these are fundamental to all 

 living activity, and are, after all, the real phe- 



