70 LEONELL C. STRONG 



Little and Tyzzer concluded that the simultaneous presence of 

 from twelve to fourteen mendelian factors which were character- 

 istic of the Japanese waltzing race was necessary for the pro- 

 gressive growth of the transplanted tissue under consideration. 

 They thus placed the inheritance of susceptibility to transplanted 

 tumor tissue on mendelian grounds. 



Working with a sarcoma (J. W. B.), Doctors Tyzzer and Little 

 were enabled to verify their first conclusion based on the car- 

 cinoma, J. W. A. In this second case the results obtained were 

 simpler and even more convincing. The parent stocks and 

 their Fi hybrids behaved as before. The F2 generation, how- 

 ever, gave twenty-three susceptible to sixty-six non-susceptible 

 animals. By the use of back-crossing (produced by crossing 

 the Fi individuals to the non-susceptible race), Doctor Little 

 ('20) was able to analyze the mendelian factors more fully. The 

 conclusions arrived at by this second analysis were: 



(1) That from 3 to 5 factors — probably four — are involved in deter- 

 mining susceptibility to the mouse sarcoma J.W.B. 



(2) That for susceptibility the simultaneous presence of these factors 

 is necessary. 



(3) That none of these factors is carried in the sex (X) chromosome. 



(4) That these factors Mendelize independently of one another. 



c. Mutation hypothesis. Theorizing from the Japanese waltz- 

 ing mouse experiments. Doctor Tyzzer, in a general paper on 

 ''Tumor Immunity," suggested that the cause of spontaneous 

 neoplasms may be due to some sort of mutational process. The 

 process of mutation is accepted by most modern geneticists as 

 the cause underlying the production of diverse variations within 

 a species. (In 1908, Williams made a statement to the effect 

 that the cause underlying the tumor-cell formation may be 

 analogous to the phenomenon known as mutation. He must 

 receive the credit, therefore, of being the first to suggest such a 

 possibility.) ■ 



