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 
Ioo 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 in 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 
