INHERITANCE OF MENTAL DEFECTS AND DISEASE 45 
estimations of the percentage of cases attributable to a hereditary 
diathesis. Toulouse (Les Causes de la Folie) cites a number of 
authorities whose estimates vary from 15.5 per cent to go per 
cent. Some writers have placed the percentage of insanity due to 
heredity often as low as 3 per cent. The disagreements are about 
as great among recent writers as among the older ones. Tanzi 
(\fental Diseases, p. 61) states that, “The percentages of heredity 
among the insane are not very high. To succeed in making them 
large, it is necessary to take into account metamorphoses from a 
nervous disease, or even from any disease, to a nervous disease, to 
consider anomalies as morbid processes, and to allow all cases of 
dissimilar heredity to pass as true heredity.” And after com- 
menting on the difficulty of securing data on the remote heredity 
of patients, Tanzi concludes: “‘If all these reservations be taken 
into consideration we arrive at the conclusion that, among the 
cases of insanity, the external act more widely than the internal.” 
Paton in his work on Psychiatry tells us: ‘There is so much glib 
talk about the problems of heredity that the uninitiated are led to 
believe that a great deal is definitely known regarding the trans- 
mission of normal and abnormal mental traits; indeed, many 
alienists fail to appreciate our limitations in this respect. At 
present we do not possess an accumulation of carefully collected 
clinical data from which it is justifiable to draw any really val- 
uable deductions, nor can the meagre facts recorded in the aver- 
age clinical history be analyzed in such a way as to make clear 
their bearing upon the biological problems under discussion.” 
Dr. Maudsley, who has given the subject particular attention, 
says: ‘‘The main value of the many doubtful statistics which 
have been collected by authors in order to decide how large a part 
hereditary taint plays in the production of insanity, is to prove 
that with the increase of opportunities of obtaining exact informa- 
tion the greater is the proportion of cases in which its influence is 
detected; the more careful and exact the researches the fuller is 
the stream of hereditary tendency which they disclose. Esquirol 
noted it in 150 out of 264 cases of his private patients; Burrows 
clearly ascertained that it existed in six-sevenths of the whole of 
