INHERITANCE OF MENTAL DEFECTS AND DISEASE 55 



France than elsewhere, while in Germany, especially in the last 

 two decades, the belief in a greater fidelity of transmission has 

 become somewhat more prevalent. The diverse results obtained 

 by different investigators on this question are in part due to 

 different categories of classification adopted. It is generally 

 recognized that a satisfactory classification of the varied forms of 

 insanity has not yet been attained. In addition to a few broad 

 types of insanity that are generally recognized there are so many 

 cases whose grouping is at present an arbitrary proceeding that a 

 certain amount of disagreement among different investigators is 

 inevitable. However, with a closer study of s^inptoms and a 

 more careful comparison of the insane who are members of the 

 same family it is coming to be recognized by an increasing num- 

 ber of writers of all countries that there are some types of insanity 

 which show a fair amount of constancy in their mode of trans- 

 mission. This is in part due to the elimination in such studies of 

 cases which are caused by external factors, such as syphilis, which 

 is now known to be responsible for general paresis and a number 

 of cases of insanity manifested in other ways. 



Apparently ,^ therefore, along with a considerable range in the 

 manifestation of "neuropathic equivalents" there is a certain 

 tendency for special types of mental disorder to perpetuate them- 

 selves.^ It is a matter of great difficulty to determine how far 

 different people with the -same inheritance of neuropathic traits 

 might come to differ in their symptoms. It is unfortunate that 

 identical twins are not more common, since observation on a 

 number of such twins with a neuropathic inheritance would 

 throw much light on this problem. 



There are a few cases of very similar types of insanity recorded 

 in twins who were apparently identical (See Galton's Inquiries 



1 Among those who have emphasized the predominance of "similar" heredity are 

 Griesinger, Ziehen, Albrecht, Sioli, Harbolla, Vorster, Schlub, Damkohler, Former, 

 Kreichgauer, Jolly, Pilcz, Berze, Myerson, Frankhauser. Of those holding to the 

 predominance of "dissimilar" heredity may be mentioned Ribot, Demay, 

 Urquhart, Schiile, Krafft-Ebing, Kraepelin (in earlier writings), Salgo, Leidesdorff, 

 Moebius, Jung, Elbe, Grassmann, Krause, Lundborg, Liepmann, Bing, Krause, 

 Croq, Dej^rine, Bumke. 



