THE LAWS OF VARIABILITY. 69 



forty. Other cerebral affections sometimes follow the 

 same rule — for instance, epilepsy and apoplexy. A woman 

 died of the latter disease when sixty-three years old ; one 

 of her daughters at forty-three, and the other at sixty- 

 seven : the latter had twelve children, who all died from 

 tubercular meningitis. I mention this latter case because 

 it illustrates a frequent occurrence, namely, a change in 

 the precise nature of an inherited disease, though still 

 affecting the same organ. 



Two brothers, their father, their paternal uncles, seven 

 cousins, and their paternal grandfather, were all simi- 

 larly affected by a skin-disease, called pityriasis versicolor ; 

 " the disease, strictly limited to the males of the family 

 (though transmitted through the females), usually ap- 

 peared at puberty, and disappeared at about the age of 

 forty or forty-five years." The second case is that of four 

 brothers, who, when about twelve years old, suffered 

 almost every week from severe headaches, which were 

 relieved only by a recumbent position in a dark room. 

 Their father, paternal uncles, paternal grandfather, and 

 grand-uncles all suffered in the same way from headaches, 

 which ceased at the age of fifty-four or fifty-five in all 

 those who lived so long. None of the females of the 

 family were affected. 



CAUSES OF NON-INHERITANCE. 



Animals and A large number of cases of non-inheritance 

 Plants, vol. ar e intelligible on the principle that a strong 

 ^ page ' tendency to inheritance does exist, but that it 

 is overborne by hostile or unfavorable conditions of life. 

 No one would expect that our improved pigs, if forced 

 during several generations to travel about and root in the 



