MENTAL CHARACTERS IX MAN 157 



to be usually a typical dominant character in in- 

 heritance. While the feebleminded may be con- 

 sidered to form a graded series, insanity is much 

 more varied in its manifestations, and is to be regarded 

 as a pathological condition working havoc with the 

 normal mental mechanism, rather than a simple 

 defect of mental machiner}^ Some types of insanity 

 may only appear late in life and yet are inherited, 

 showing that the seeds of ultimate derangement aru 

 present in the germ plasm. In other cases, an 

 exceptional mental or physical strain may bring out 

 phenomena of insanity which would never appear 

 under ordinary circumstances. 



Ordahl (191 9) made a study of fifty families in 

 California containing feeblemindedness. He con- 

 cludes that the parents of the feebleminded are often 

 borderline cases and escape detection by ordinar}- 

 means. Seventy-two per cent, of the fifty families 

 showed defective inheritance. Of the living children, 

 5*6 per cent, were idiots, 15-6 per cent, imbeciles, 

 26-2 per cent, morons, 3-1 per cent, dull normal, 

 1-2 per cent, psychopathic, 48-1 per cent, normal. 

 Ordahl believes that the moron and dull normal can be 

 detected by expert means in the earl}' school 3'ears. 

 Otis (191 6) aims to reconcile the views of Pearson and 

 Davenport. He considers it important to distinguish 

 between intelligence and " brightness " — i.e., the 

 degree the child is in advance of the normal develop- 

 ment of intelligence. Pearson showed that all degrees 

 of intelligence (meaning brightness) exist, but thi> 

 does not exclude the Mendelian inheritance of any 

 degree when mated with feeblemindedness. Otis 

 concludes that " the existence of all grades of bright- 

 ness, and the possibility of the universal ]\Iendelian 

 inheritance of different grades of brightness, arc- 

 therefore seen to be entirely compatible." This is in 

 accord with much other Mendelian behaviour. 



