196 ACQUIRED CHARACTERS sec. 



" By far the most important cause of insanity is the 

 transmission of psychopathological tendencies, especially of 

 cerebral infirmities, by means of procreation. 



" The fact of the heredity of psycliical defects and diseases 

 was known even to Hippocrates. It is only the special action 

 within the limits of this province of a general biological law 

 which plays a stupendous part in the organic ^vorld, on which 

 indeed the whole progress of the human race depends. 



" After tuberculosis there is scarcely a class of diseases in 

 which heredity works so powerfully as in psychical diseases, 

 but on the percentage of cases in which its effects are evident 

 authorities differ. The percentage of cases determined by 

 heredity given by statisticians (Legrand du Saulle, o'p. cit. 

 p. 4), varies from 4-90 per cent. It is obvious that a constant 

 factor cannot produce effects in such a variable manner. The 

 cause of the difference can only lie in the different method 

 by which the statistical analysis was produced. Much 

 depends on tlie question, from what classes of people the 

 material of the statistics was derived. In aristocratic circles, 

 in communities secluded from intermixture with surrounding: 

 peoples, in exclusive religious societies (Jews, sectarians, 

 Quakers), where close interbreeding is practised, the percentage 

 of hereditary cases is greater than in a floating population. 

 But the point of view of the different statisticians has also been 

 different. Many investigators have only recognised heredity 

 when insanity could be proved in the parents (direct similar 

 inheritance). But the definition of heredity cannot be so 

 narrowly limited. Three essential facts are here to be con- 

 sidered. 



1857 ; Idem, Archiv. gener. September, 1859 ; Hohnbaum, AUgein. Zeitschr. f. 

 Psych. 5, p. 540 ; Morel, Traite des Maladies mentales, pp. 114, 258; Ibid., 

 De Vheredite viorbide progressive, Archiv. gener. 1867 ; Voisin, Gaz. des. H6pit. 

 1858, 16; Moreau, V Union medic. 1852, 48; Jung, Allg. Zeitschr. f. Pschy. 

 21-23, Ann. Med. Psych. November 1874 ; Legrand du Saulle, Die erhliche 

 Geistesstorung, German by Stark, 1874 ; Ribot, Die ErUichkeit, German by 

 Hotzen, 1876 ; Hagen, Statist. Untersuch. Erl. 1876, 



