INHERITANCE OF MENTAL DEFECTS AND DISEASE 45 



lestimations 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 90 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 

 {Mental 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 



