INHERITANCE OF MENTAL DEFECTS AND DISEASE 33 



minded. If, on the other hand, the two parents lack different 

 socially significant traits, so that each parent brings into the com- 

 bination the traits that the other lacks, all of the children may 

 be without serious lack and all pass for ' normal. ' ' 



This change of front is due to the discovery of several cases in 

 which it was alleged that normal individuals were produced by 

 parents both of whom were mentally defective. In fact the 

 percentage of such cases was rather high. Considering both low 

 grade and high grade feeble-mindedness together it was found 

 that the percentage of defectives resulting from nulliplex matings 

 (feeble-minded X feeble-minded) was only 77.3 per cent instead of 

 100 per cent. Matings of normal N N with feeble-minded n n 

 give 37.5 per cent of defectives instead of none which would be 

 expected even on Danielson and Davenport's own hypothesis. 

 No explanation, however, of the latter discrepancy is offered. 



Chances for error in the investigation of the mentality of such 

 communities as the Hill Folk are numerous as the authors seem 

 to realize. "The problem that a field worker meets is to analyze 

 each person in the pedigree in respect to his mental and moral 

 traits from a complete acquaintance and from a comparison of the 

 description of others. After all the evidence from personal visits, 

 interviews with relatives, physicians, town officials, and reliable 

 neighbors, and facts from court and town records have been 

 collected, it is, even then, difficult to represent these characteris- 

 tics exactly by the standard symbols which are used for the 

 biological study of inherited traits. The distinction between an 

 ignorant person who has normal mental ability and a high-grade 

 feeble-minded one who has not, is often as impossible to make 

 as that between medium and low grade feeble-mindedness." 



A careful examination of the Hill Folk will show that it exhibits 

 little internal evidence of critical judgment, which is so necessary 

 in dealing with the inheritance of mental defect. We find in 

 examining the alleged matings of feeble-minded with feeble- 

 minded that m one case all that is said of the mental state of .one 

 consort is that he was "a wild immoral fellow"; of another, that 

 he was "a plodding dull drinking fellow"; of another, that he 



