Physiological and Psychological Heredity. 267 



should either be strictly deduced from some unquestionable 

 biological law, or else it would have to be possible to give 

 experimental proof of it in all possible cases. We can do neither 

 of these things. But we hold that this thesis possesses all the 

 probability that accompanies the inductive process ; we hold that 

 were our science sufficiently advanced, we could, the state of the 

 brain being given, thence deduce the corresponding thought or 

 sentiment ; and, conversely, the sentiment or thought being given, 

 we could deduce the state of the brain. Leibnitz, whose genius 

 was all-penetrating, had a glimpse of this truth at a period when 

 science scarce allowed a suspicion of its existence. 'All that 

 ambition led Caesar's mind to do is represented also in his body ; 

 there is a certain state of the body which answers even to the 

 most abstract reasonings.' 



We might have deduced our proposition from what was before 

 said ; for if it be admitted that the physical and the moral differ 

 not objectively but subjectively not in their nature, but as to the 

 mode in which they are known to us ; if vital phenomena are 

 on the one hand specially mental, and on the other specially 

 physical, but yet such that each of them, taken in its totality, is 

 ever both physical and mental ; then it is plain that every psych- 

 ological phenomenon supposes a corresponding physiological state. 

 But we have thought it best to establish this truth directly, and by 

 experience, independently of all hypotheses. We need only add 

 that here, as everywhere, our solution is restricted to phenomena, 

 and has nothing to do with the ultimate reasons of things. 



CHAPTER III. 



PHYSIOLOGICAL AND PSYCHOLOGICAL HEREDITY. 

 I. 



IF we sum up what has been said in the two foregoing chapters, 

 we shall see that in consequence of these researches the problem, 

 What is the cause of psychological heredity ? is very much sim- 

 plified. 



In the first place, we endeavoured to show that the general 



