Xo. 641] INHERITANCE OF CANCER IN MICE 527 



The most striking confirmation of this view has in recent 

 years been funished by Miss Slye, who discovered certain 

 families of mice in which a tendency to special cancers, 

 as, for instance, cancer of the liver, was inherited. We 

 therefore conclude that inheritance to cancer consists in 

 general in a tendency to the inheritance of a particular 

 kind of cancer. This agrees also with the results of Miss 

 Stark, who found in Drosophila two specific kinds of in- 

 heritable, tumor like formations originating by mutation. 



12. Our continued investigations have thus borne out 

 our earlier conclusion that the endemic occurrence of 

 cancer among animals is due to this hereditaiy trans- 

 mission of the disposition to cancer. In addition, infec- 

 tion with certain metazoon parasites which act as an 

 external stimulus comparable to the action, for instance, 

 of Roentgen rays, may play a part in certain cases ; but 

 oven here the metazoon parasites seem to act on a basis 

 of hereditarily transmitted disposition. The observa- 

 tions of Fibiger, with which the recent findings of Eoh- 

 denburg are in agreement, suggest this conclusion. 



13. While these statomont.; ap])ly dircH'tly oiilv to an- 

 imals, the evidence (ui hand innkcs il pi'()]);il)l(' that, in 

 •principle, conditions arc siiullai" in man: liciv :\\<o in all 

 probability one or more factors aw liciT(litari]\- trans- 

 mitted which determine the intensity in the tcinlcncN to- 

 wards cancer development. In man tlii- ttMidciicx- lias, 

 however, in many eases been more or less (MjnaliztMl among 

 different families as a result of long continued cross 

 breeding (10). Wherever this factor can be eliminated 

 as among different races which remained relatively pure 

 or among a very stationary population, as in certain 

 parts of Norway, the evidence points to the com-hision 

 that here too marked differences in the tnidcncy loward'^ 

 cancer exist in various strains and races (11). i:ven 

 among the ordinary population some (vca-i.mal -trlkiiig 

 findings very strongly suggest this view. 



Furthermore, Davenport (12) has sliown that flic tend- 

 ency to neurofibromatosis is hereditarily transmitted as 



