46 THE BEGINNINGS OF LIFE. 



is there something like a constant ratio between the 

 physical antecedent and the psychical consequent.' 



From all this it may be imagined how hopeless the 

 attempt would be to establish anything like a quanti- 

 tative estimate of the amount of force answering to 

 these different results of the activity of the Nervous 

 System. In considering the question of muscular acti- 

 vity and its correlation with physical force, we have to 

 do with a measurable effect under the form of mecha- 

 nical energy. But the manifestations of the activity 

 of the nervous system are much more subtle and elud- 

 ing. How is it possible for us to estimate the value of 

 the energy expended in regulating the nutrition of the 

 body? How, in a motor act, shall we separate what 

 is due to the nerve and what to the muscle ? nay, 

 where Feeling is aroused, where Consciousness appears, 

 how shall we estimate the equivalent value of this, 

 which each one knows in himself alone, and which 

 seems to differ so absolutely from everything else in 

 the universe ? However probable it may be that what 

 we know as Sensation and Thought are as truly the direct 

 results of the molecular activity * of certain nerve- 

 centres, as mechanical energy is the direct result of a 

 muscle, this cannot be proved. MM. Beclard and 

 Heidenhain have shown us how, when a muscle con- 

 tracts, an amount of heat disappears which holds a 



1 For some most admirable and suggestive remarks as to the probable 

 unit of Consciousness, we would refer the reader to Mr. Spencer's ' Princi- 

 ples of Psychology,' No. 21, pp. 148-158. 



