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 symptoms 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, Vérster, Schlub, Damkéhler, Forster, 
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, Eibe, Grassmann, Krause, Lundborg, Liepmann, Bing, Krause, 
Croq, Déjérine, Bumke. 
