94 MARRIAGE AND HEREDITY 



be fought out in the field of moral characteristics. 

 There it has encountered, and still encounters, more 

 prejudice than any scientific doctrine enunciated 

 since the time of Galileo ; and there is certainly no 

 question as to its subversive effect upon many of our 

 social institutions. The line of demarcation between 

 physical and moral characteristics is one extremely 

 difficult to draw. In what category are we to place 

 suicidal and homicidal tendencies, drunkenness and 

 sensuality, for example ? The truth is, that although 

 we adopt a classification of physical and moral attri- 

 butes in speaking or thinking of this subject, nature 

 recognises none, the operations of the body and mind 

 being intimately, nay indissolubly, bound up with 

 each other. If physiologists have not yet succeeded 

 in assigning all mental functions to a definite set 

 of physical causes, they have gone far towards 

 doing so, and our knowledge of the subject, thanks 

 to the labours of specialists in England, France, Ger- 

 many, and Italy, may be said to be daily widening. 



At the head of mental characteristics, whose heredi- 

 tary nature is apparent, we may place idiocy and 

 insanity. The idiot is born with an undeveloped 

 brain, and he transmits his imperfections either 

 directly or indirectly. Whether in the case of mind 



