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 formulae 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 is not 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- 



