No. 641] INHERITANCE OF CANCER IN MICE 



519 



instance, that in the Cream-English hybrids the mother 

 strain was considerably more often predominant than the 

 father strain ; in addition, we found that in reversing a 

 cross different results were obtained in accordance with 

 the difference in the tumor rate of the motlier strain. It 

 is, however, possible that these occurrences are chance 

 phenomena and we offered this interpretation merely as 

 a suggestion. 



6. Our investigations make it possible to express in a 

 quantitatively definite manner the hereditary tendency 

 to cancer in individual strains of mice, the figures vary- 

 ing in different strains between zero and 100. This he- 

 reditary tendency is, however, not a simple quantity, but 

 composite, because 



(a) The hereditary disposition to cancer is probably 

 due to the cooperation of nmltiple factors. The r(^sults 

 of hybridization, which essentially were of an inter- 

 mediate character, the fact that all kinds of intergrades 

 between father and motlier strain exist and that all pos- 

 sible variations in the hereditary tendency to cancer exist 

 in different strains, and that the hercditai-y tendency 

 determining the cancer age is not enlirel\- ideiiticnl with 

 the tendency expressed in the cancer rale, xcry strDiiuly 

 suggest this conclusion. Variations in the nnnil>ei" and 

 charaet.'r of the ]nn]tii)le factors in the .liffei'ent iii.llvid- 

 uaK max l e responsible f.-r the ^ariatioll. in inien^ty 

 whieh determine tin- tendein-x to caneerin in.lix idnaU. and 

 (lilTfi-ent strain^iuaN .liffera-^ tothmn-an in the diMi'ibii- 

 tion of the factor^ anion- the in<lividnaN helonulnu to tin- 

 ^strain. Thn-^ we nia> a^Mini.' that the ^irain^ Knuli^h. 



average a greatei- nninhei' n\ taeioi-> than the lin!i\ idnals 

 of the strain Cream ,iml (imtinn ^ and nn'inv ..tiir,-.: 

 and it would be eonceiv al>h' thai m nian> ca-es a 

 tumor mouse belonuinu to the >tr;iin l-hi<;h-h differs 

 from a tumor mouse in the strain ( ivani, the t'oi-mer 

 often exceeding the nilninium of faetoi> nrecvv.n-y for 

 the production of tumors. 



