ISO HEREDITY AND EUGENICS 



are hereditary. In hereditar}^ feeblemindedness the 

 children tend to have about the same grade of 

 mentality as the parents. Sometimes accidents in 

 childhood reduce an hereditary moron to imbecility 

 or idioc}^ When their mentality is under five years, 

 individuals rarely become parents, but parenthood 

 with a mental age of seven or eight is common. 



The careful training methods of the Vineland In- 

 stitution show that it is impossible to develop a mind 

 beyond its inherited capacity. The mental develop- 

 ment may stop at any point, and training cannot push 

 it any further, although the most patient and per- 

 sistent efforts have evidently been made in this 

 direction. When mental progress ceases, it is neces- 

 sary to turn to manual training for any further 

 development of the individual. 



As regards inheritance, Goddart cites 42 matings, 

 NF? xFFc^ — i.e., a heterozygous but normal mother 

 and a feebleminded father — producing 144 children 

 whose mentality is known. Of these, 71 were feeble- 

 minded and 73 normal, almost exactly in accord with 

 the Mendelian expectation of equality. On the other 

 hand, from 6 matings FF ? xNFr? there were 193 

 children whose mentality is known, and they were 

 122 feebleminded to 71 normal. Hence it appears 

 that the number of feebleminded considerabl}^ exceeds 

 expectation w^hen the mother is feebleminded. Again, 

 in NFxNF matings (26) there were 185 offspring, 

 and the mentalit}^ of 122 was determined, 83 being 

 normal to 39 feebleminded (expectation for one 

 Mendelian difference, 91 -5: 30-5). Among 476 chil- 

 dren from FF x FF matings, only 6 are recorded 

 as normal, and these were no doubt border-line cases, 

 or perhaps illegitimate. Hence the evidence clearl}- 

 favours the interpretation of feebleinindedness as a 

 simple recessive. 



Holmes (1921) and other writers are less willing 



