54 THE STORY OF LIFE'S MECHANISM. 



times called the vegetative functions) the laws 

 of chemistry and physics furnish adequate ex- 

 planation. 



We must now look a little further, and question 

 some of the functions the mechanical nature of 

 which is less obvious. The whole operation thus 

 far described is under the control of the nervous 

 system, which acts somewhat like the engineer 

 of an engine. Can this phase of living activity 

 be included within the conception of the body 

 as a machine 1 



Nervous System. When we come to try to 

 apply mechanical principles to the nervous 

 system, we meet with what seems at first to be 

 no thoroughfare. While dealing with the grosser 

 questions of chemical compounds, heat and 

 motion, there is little difficulty in applying 

 natural laws to the explanation of living pheno- 

 mena. But the problem with the nervous system 

 is very different. It is only to-day that we are 

 finding that the problem is open to study, to say 

 nothing of solution. It is true that mental and 

 other nervous phenomena have been studied for 

 a long time, but this study has been simply the 

 study of these phenomena by themselves without 

 a thought of their correlation with other pheno- 

 mena of nature. It is a matter of quite recent 

 conception that nervous phenomena have any 

 direct relation to the other realms of nature. 



Our first question must be whether we can 

 find any correlation between nervous energy and 

 other types of energy. For our purpose it will 

 be convenient to distinguish between the pheno- 

 mena of simple nervous transmission and the 



