TRANSFORMATION AND EQUIVALENCE OF FORCES. 223 



" But how," it may be asked, " can we interpret by the 

 law of correlation the genesis of those thoughts and feelings 

 which, instead of following external stimuli, arise spontane- 

 ously? Between the indignation caused by an insult, and 

 the loud sounds or violent acts that follow, the alleged con- 

 nexion may hold; but whence come the crowd of ideas and 

 the mass of feelings that expend themselves in these demon- 

 strations? They are clearly not equivalents of the sensa- 

 tions produced by the words on the ears; for the same words 

 otherwise arranged, would not have caused them. The 

 thing said bears to the mental action it excites, much the 

 same relation that the pulling of the trigger bears to the 

 subsequent explosion does not produce the power, but 

 merely liberates it. Whence then arises this immense 

 amount of nervous energy which a whisper or a glance may 

 call forth? " The reply is, that the immediate cor- 



relates of these and other such modes of consciousness, 

 are not to be found in the agencies acting on us externally, 

 but in certain internal agencies. The forces called vital, 

 which we have seen to be correlates of the forces called 

 physical, are the immediate sources of these thoughts and 

 feelings; and are expended in producing them. The proofs 

 of this are various. Here are some of them. It is a 



conspicuous fact that mental action is contingent on the 

 presence of a certain nervous apparatus; and that, greatly 

 obscured as it is by numerous and involved conditions, a 

 general relation may be traced between the size of this appa- 

 ratus and the quantity of mental action as measured by its 

 results. Further, this apparatus has a particular chemical 

 constitution on which its activity depends; and there is one 

 element in it between the amount of which and the amount 

 of function performed, there is an ascertained connexion: 

 the proportion of phosphorus present in the brain being the 

 smallest in infancy, old age and idiotcy, and the greatest 

 during the prime of life. Note next, that the evo- 



lution of thought and emotion varies, other things equal, 



