26 SOME POSSIBLE BEARINGS OF GENETICS ON PATHOLOGY 



essary to work with a simpler situation where fewer factors are 

 involved; possibly such a case as that of the Jensen tumor will 

 furnish proper material, but it will be necessary to work with pedi- 

 greed material rather than with " Danish," " French," " Ger- 

 man." or even English breeds of mice. 



In plants also the inheritance of immunity of wheat to rust 

 has been studied. Biffen's results with wheat are those best 

 known. An immune race crossed to a susceptible race gave first 

 generation plants that were attacked. This means that immu- 

 nity is a recessive character. In the next generation there were 

 64 immune and 194 affected plants (a 1 13 ratio). If the im- 

 mune plants are self-fertilized, they yield onlv immune plants in 

 later generations. 



Xilsson-Ehle and Vavilov think that such simple relations are 

 rather the exception than the rule. Vavilov found that Persian 

 wheat, immune to mildew, crossed to different susceptible species 

 produced offspring that were immune in 13 combinations. In 

 these cases immunity is dominant. 



In the next generation several degrees of resistance were 

 noted — and a few plants were even more susceptible than their 

 grandparents. 



It is interesting again to note that susceptibility and immunity 

 are species and variety characters in these cases, but this does 

 not mean that the differences are not Alendelian. It suggests 

 however the possibility that several or many factor differences 

 are often involved. 



There is no more interesting field in which genetics and pa- 

 thology meet than that of cancer. I realize how careful we on 

 our side must be in discussing this question with you who are 

 experts, nevertheless there are certain aspects of the problems 

 of cancer from the genetic side that I may be allowed briefly to 

 mention — not, however, without some misgivings. 



Suppose all men over seventy-five died of arteriosclerosis. 

 Could one say that hardening of the arteries is inherited? I 

 think that it would be proper to use the word heredity to include 

 such a case, but we would not know how it was inherited unless 



