212 HEREDITARY PREDISPOSITION TO DISEASE. 



as in the case of the lungs, state a sound original 

 constitution as the first condition of its healthy ac- 

 tion. If the brain possess from birth a freedom 

 from all hereditary taints and imperfections, and 

 have acquired no unusual susceptibility from inju- 

 dicious treatment in infancy, it will withstand a great 

 deal in after-life before its health will give way. 

 But if, on the other hand, either it inherit deficien- 

 cies, or early mismanagement have subsequently 

 entailed upon it an unusual proneness to morbid ac- 

 tion, it will give way under circumstances which 

 would otherwise have been perfectly innocuous; 

 and, accordingly, it may be truly said, that the most 

 powerful of all the causes which predispose to nervous 

 and mental disease is the transmission of a heredi- 

 tary tendency from parents to children, producing in 

 the latter an unusual liability to the same maladies 

 under which the parents have laboured. 



Even where the defect in the parent is merely 

 some peculiarity of disposition or temper, amount- 

 ing perhaps to eccentricity, it is astonishing how 

 clearly its influence on some one or other of the 

 progeny may be traced, and how completely a con- 

 stitutional bias of this description may interfere 

 with a man's happiness or success in life. I have 

 seen instances in which it pervaded every member 

 of a family, and others in which it affected only one 

 or two. When the original eccentricity is on the 

 mother's side, and she is gifted with much force of 

 character, the evil extends more widely among the 

 children than when it is on the father's side. Where 

 both parents are descended from tainted families, 

 the progeny is of course more deeply affected than 

 where one of them Ls from a pure stock ; and, seem- 

 ingly for this reason, hereditary predisposition is a 

 more usual cause of nervous disease in the higher 

 classes, who intermarry much with each other, than 

 in the lower, who have a wider choice. 



Unhappily, it is not merely as a cause of disease 



