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THE AMERICAN NATURALIST [Vol. LY 



posed to bring about a multiplicity of tumors or cor- 

 responding malformations. 



In a similar manner Maud Slye states there is in mice 

 inherited a general tendency to cancer. In hybrid strains, 

 according to this author, this general tendency finds ex- 

 pression in the first hybrid generations in a tendency to 

 develop sarcoma, while in subsequent generations more 

 specialized tissues are affected which develop into car- 

 cinoma, and in still later generations multiple tumors are 

 prone to appear. 



We have not been able to observe such a cycle in our 

 utrains of mice. We had uniformly in all generations to 

 deal with mammary carcinoma and in many autopsies 

 which we made of tumor mice we failed to observe other 

 kinds of tumors. This does not exclude the possibility 

 or even probability that occasionally lesions may have 

 been present in other mice which were tumors of a differ- 

 ent kind. We described, for instance, a beginning squa- 

 mous cell carcinoma in a mouse afflicted with a mammary 

 :^ancer about 10 years ago ; but on the whole such occur- 

 i-ciioos wciT rare and they could not be interpreted as due 

 to tli<' iiih. ritance of a general tendency to cancer; in each 

 (■a<r t'xtiTii.il factors would then at least partially deter- 

 iiiiiu' which particular expression this general tendency 

 should find. 



In our strains there was inherited essentially, not a 

 general tendency to tumor formation, but a specialized 

 tendency to cancer of the breast. This does not exclude 

 the possibility that in certain strains a tendency to the 

 development of another kind of tumors may have been 

 inherited side by side with the tendency to mammary 

 (■aiKMM-. In favor of this conclusion we may cite the ex- 

 periences in cases of the so-called endemic occurrence of 

 cancer, as, for instaTicc the caiicrr of the inner canthus of 

 the eye in cattle olxerwd bv us in 1899, the cancer of the 

 scrotum in tlie rat olt-ci x cl hy Manau, our o])servations 

 of sarcoma of the thyroid -land in the rat. All these are 

 instances of the inheritance of specific kinds of cancers. 



