32 SOME POSSIBLE BEARINGS OF GENETICS ON PATHOLOGY 



He has guarded against abnormalities in his stock by using pedi- 

 greed material. The malformations that reappear in successive 



generations are general rather than specific. Such organs as the 

 eve are those hardest hit. but this is supposed to be rather a by- 

 product of the general debility of the individual. Stockard 

 points out that the alcohol has affected the germ cells, and it is 

 through these that the effects are transmitted. Now if one or 

 more genes had been permanently changed we should expect to 

 have evidence of Mendelian inheritance. The results do not show 

 convincingly that the inheritance is not Mendelian, but it does 

 not appear to be so. There is another possibility. Recent re- 

 sults have shown that rarely entire blocks of genes — pieces of 

 the chromosomes — may be duplicated (owing to imperfect sepa- 

 ration) or pieces may be lost. Here the effects on the organism 

 are more far-reaching than when a single gene is changed. It 

 remains to be discovered whether, in some such way as this, 

 Stockard's remarkable results may be brought into line. 



Guyer injected the crushed lens of rabbits into fowls. From 

 the blood of the fowl he obtained serum that was injected into 

 pregnant rabbits. The offspring of these rabbits whether male 

 or female often had defective eyes and lenses. The defect was 

 even transmitted to later generations. Here also the germ cells 

 of the embryo may be changed by serum that at the same time 

 affects the development of the eyes of the embryo in utero. 



If this is the case we should expect, as Guyer pointed out, 

 that the germ cells of the pregnant mother (into which the serum 

 was injected) would also show effects. It should have been a 

 simple matter to show this by a proper test. The test that Guyer 

 made, namely by out-breeding the mother and finding no defec- 

 tive F x young, was quite inadequate if, as appears to be the case, 

 the character is a recessive. 



It is important to keep clearly in mind that there are two dis- 

 tinct questions involved in these three cases. Genetics has to 

 deal with only one of them. There is first the question of the 

 action of environment on the germ cells. Genetics has nothing 

 to do with this question. There is then to be determined whether, 



