IMPROVING THE HUMAN PLANT 



at any rate, immunity to disease appears to be 

 dominant and susceptibility recessive, so that the 

 offspring of an immune and a susceptible indi- 

 vidual are all immune. 



This appears to be the case, for example, with 

 susceptibility to tuberculosis. 



The children of an immune and a susceptible 

 person appear to be immune, or relatively im- 

 mune, to the disease. And this is obviously a fact 

 of the very highest practical importance. 



But we must recall that the children who are 

 thus individually immune contain in their germ 

 plasm the factors for susceptibility. So such indi- 

 viduals should exercise the utmost precaution not 

 to marry into families where there is a corre- 

 sponding taint of susceptibility to tuberculosis, 

 even though the individuals they select as mar- 

 riage partners are themselves healthy. 



Here as in the other case just cited, the union 

 of two individuals who carry the hereditary fac- 

 tors of susceptibility submerged in their germ 

 plasm will result in the reappearance of suscep- 

 tibility as a tangible trait in about one in four of 

 the offspring. 



Stated otherwise, in more general terms, it ap- 

 pears that there are a good many human traits 

 that are blended in such wise in the offspring of a 

 given pair of parents who present the trait, as to 



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