THE APPLICATION TO MAN 309 



vague terms are made up of a multitude of diverse con- 

 ditions each of which must have a different array of 

 determiners and, in the second place, because any one 

 definite sort of insanity or imbecility may be condi- 

 tioned by a variety of factors. 



However, the difficulty of the problem is no reason 

 for abandoning the attempt to reach its solution and 

 to learn, if possible, "whence come our 300,000 insane 

 and feeble-minded, our 160,000 blind or deaf, the 

 2,000,000 that are annually cared for by our hospitals 

 and homes, our 80,000 prisoners and the thousands of 

 criminals that are not in prison, and our 100,000 pau- 

 pers in almshouses and- out" (Davenport). 



7. THE CONTROL OF DEFECTS 



The method of possible control of human defects 

 depends upon whether they are positive or negative, 

 that is, dominant or recessive. In those cases where 

 a given defect is due to a single determiner the 

 Mendelian expectation for the possible offspring 

 arising from various matings is indicated in the 

 table on page 310 in which D stands for the defect 

 and d for its absence. 



If the defect is positive and in a duplex or homo- 

 zygous condition in one parent, as in 1, 2, and 4 

 all the offspring will possess it regardless of the ger- 

 minal constitution of the other parent. In two cases 

 only, namely, in 3 and 5, where the defective parent is 

 heterozygous, is there any chance of unaffected off- 

 spring, and even in these cases the defect is quite as 



