388 THE POPULAR SCIENCE MONTHLY. 



MORBID HEREDITY. 



By M. CH. FEKE. 



THE study of morbid heredity is full of interest, because the 

 knowledge of its laws may assist us in finding preventive 

 measures against it, and because it may thereby be a means of 

 comforting persons who are under those laws. In seeking a defi- 

 nition of morbid heredity, we first take Sanson's definition of bio- 

 logical heredity as the transmission from ascendants to descend- 

 ants, by sexual generation, of natural or acquired properties. 

 With acquired properties we may include morbid ones. Heredity 

 of morbid properties seems to obey the same law as heredity of 

 natural properties, for which we may accept Darwin's formulas 

 of 1. The law of direct and immediate heredity, under which 

 parents tend to transmit their physical and moral characteristics 

 to their descendants. 2. The law of predominance of direct hered- 

 ity, under which the character of one of the two progenitors is 

 predominant in the product. 3. The law of heredity in reversion, 

 racial heredity, which is applicable to the often-observed facts of 

 atavism, or the reappearance in descendants of the characteristics 

 of a more or less remote ancestor ; and 4. The law of homochronous 

 heredity, or the reappearance of hereditary characteristics at the 

 same periods of life in ascendants and descendants. 



Morbid heredity does not inevitably obey the laws of direct 

 heredity. It is a well-known fact that diseases in morbid families 

 are not usually transmitted with a perfect likeness. The homol- 

 ogous or similar heredity, which is observed chiefly as to mental 

 diseases, is rare as to other diseases. Usually the disease is modi- 

 fied in descent. A diabetic patient produces an ataxic son, or a 

 hysterical daughter, or an epileptic child. John Hunter seems to 

 have anticipated these variations when he maintained the exist- 

 ence not of hereditary diseases proper, but of a hereditary dispo 

 sition to contract them a hypothesis which, though somewhat 

 vague, may account for dissimilar heredity and also for the fre- 

 quent happy absence of heredity. The probability of morbid 

 heredity manifesting itself is increased when both the parents 

 are attainted with the same defect. Consanguineous marriages, 

 which have been charged with being an important factor in the 

 genesis of neuropathy, of deaf-mutism, and of degeneration in 

 general, really are of effect only through the accumulation of 

 heredity. Consanguinity favors the heredity both of good and 

 of bad family qualities. In healthy families it is desirable ; in 

 morbid families it should be shunned. 



Pathological selection of nervous parties, who seem to be at- 

 tracted to one another by invincible sympathies, involves the 



