No. 641] INHERITANCE OF CANCER IN MICE 517 



Cream Y. In the substrain Cream Y the tumor rate had 

 been zero. Four generations of the offspring were ol)- 

 served comprising altogether ()8 femak^ niiee which 

 reaclied an age sulTicieiit for iiichisioii in owv rectu'ds. 

 Thirty-six of these mic.'. that is. jx-i' rent., died with 

 tumors, 11 of tliese in the lirst a-e period. 'Idiis i^ a 

 record which conie- near that of the haiuli^h Sal>h'. 

 These as well as nuinei-oiis oth<-r experiments s<.m t.. us 

 more in liai-mony with 1 he coii,-hi>ioii that niulti]>h' factor- 



in mice than tlie view of .Maud Slyc who niaintnin^ 

 that the fa<-tor for mammary cancer in mice i> a re(M's>ivc 

 monohyhri.h 



(4) Tin' age at which tumoi-> app.'ai- is ,iu>t a^ rhar- 

 act.M-istic of iiidivi.hial strains as the tumor rnW. The 

 tumor a-e i> also tran>miltc<l hy licredity. In >anw 

 sti-ains tumors appear relatively cai'ly. the i)eivcntauv of 



the lirst 'tlvelvc months is con<illei'al)ly greatc.- than in 

 otliers: and this characteristic is <m the whole just a< con- 

 stant in the strains as the tumor rate as a whole. 



We can distinguish two factor> in the inluM-itance ..f 

 the luiimr ag.': io) In g.'iieral in the strains with the 

 liigher tunu>r I'ates the tumors appear at an eai-li.T peri-nl 

 of life than in the lower tumoi' rate <train^. Thi< c<mies 

 out vei'v clearly when we divide all the strains into three 

 chisses.' tho>e with a tum..i- inci.lenee ahov 4(i i)er cent., 

 the hiuh tumor rat<' strains : tlio>e with a tumor incidence 

 between iM) pc-r cent, and 4(1 per cent., the m.Mlium tumor 

 rate strains, and tho>e with a tumor incidence heluw 



^ If we defrmine in each class the percenla-e of tumor^ 

 a])i)earin- in the different age periods, we Hnd that the 

 tumors appear the earlier in life the Id-her the tumor 

 ineidenc an.l the .litr,.rence between theditferen! eh,.... 

 is<,uite marked. 



There is in .Mir case a definite relation between die fac- 

 tors, tumor age and tumor rate. We can intei-pret this 



