52 THE TREND OF THE RACE 
grees including 206 matings and 1097 offspring. The same con- 
clusions are expressed as to Mendelian inheritance of insanity. 
The authors recognize that while neuropathic traits are recessive, 
“various clinical neuropathic manifestations bear to one another 
the relationship of traits of various degrees of recessiveness; in a 
most marked way recoverable psychoses, though recessive as 
compared with the normal condition, are dominant over epilepsy 
or allied disorders.” 
Traits on the same level of recessiveness, but differing greatly 
in their clinical manifestations may bear to one another the rela- 
tionship of ‘‘neuropathic equivalents.’ This, if true, makes 
Mendelian formule more elastic, but it increases the difficulty of 
proving that the inheritance is, in fact, Mendelian. 
The authors show a commendable caution about concluding 
that the inheritance of insanity follows simple Mendelian rules. 
They say, “It seems necessary to assume that the normal devel- 
opment and function of the nervous system is dependent not upon 
a single unit determinant in the germ plasm, but upon a group of 
determinants, and that the number of units lacking from that 
group, determines the special type of defect to be observed 
clinically. It may be recalled that a similar assumption has been 
found necessary for the understanding of the inheritance of other 
Mendelian characters, notably various shades of skin pigmenta- 
tion.” 
With commenting on the fact that it is not proven that the 
inheritance of skin color is Mendelian, although it is possible 
on certain assumptions to show how it might be so, or at least 
that it isnot certain that it is not so, there seems to be no special 
reason for the particular conclusion, ‘‘That the number of units 
lacking from the germ plasm determines the special type of defect 
to be observed clinically.” Analogy with Mendelian inheritance 
elsewhere would seem to make it more probable that the type of 
defect produced would depend upon the particular units of the 
germ plasm affected, and not merely upon their number. Perhaps 
the authors, who manifest an open-minded and candid attitude 
in dealing with the problem, would not object to this interpreta- 
