PROBLEMS CONCERNING THE TUMOR VIRUSES 363 



filtrates from one tumor was neutralized by rabbit antisera but not by 

 mouse antisera. (4) Despite the 100 % transplantability of the original 

 tumors, the filtrate-produced leukemias grew in only 10 % of the hosts and 

 serial transplantation was successful in only four instances. This was an 

 unusual finding, especially when "inbred strains" were used as hosts. 



The chief contribution studies on the viral etiology of mouse leukemia have 

 made to the tumor viruses is to arouse the active interest of many oncologists 

 and virologists. The work, thus far, has produced results of considerable 

 significance, but so much is dependent upon future studies that any further 

 conclusions would be purely speculative. 



III. Conclusion 



This chapter was written for readers who are interested primarily in 

 viruses and secondarily in an objective review of the role of these agents in 

 the causation of cancer. The virus theory of cancer requires no defense. The 

 best summation of experimental evidence in support of the theory was 

 presented by Rous (1936) more than twenty years ago, and the best reason for 

 its use in the experimental approach to the cancer problem was given by 

 Andrewes (1950) who found it "intellectually satisfying." Any concept based 

 upon sound scientific data and capable of stimulating further research is 

 certain to contribute much to knowledge of the cancer process. 



The crux of the problems of the tumor viruses is to learn more of the 

 properties of the known viruses and to expose others. Perhaps the chief 

 lesson to be learned from past experience is that almost all rewarding efforts 

 with the tumor viruses have come from working directly with tumors or with 

 the known tumor viruses. Virologists interested in cancer research should be 

 alert to advances in the entire field of virology and to the application of newer 

 knowledge to their problems. But efforts to establish a viral causation of 

 cancer by invoking analogies between the known characteristics of other 

 viruses and the cancer process would appear to be futile. 



This chapter may have been written at the poorest possible time. The 

 problems of the tumor viruses are being advanced so rapidly through excellent 

 investigations of the known viruses, the concentration of effort upon the 

 problem of mouse leukemia, and the convergence of virus research and 

 tissue culture research, that within a few years definitive answers may be had 

 to the viral causation of many other cancers. 



References 



Andervont, H. B. (1941). J. Natl. Cancer Inst. 2, 13. 

 Andervont, H. B. (1944). J. Natl. Cancer Inst. 4, 579. 

 Andervont, H. B. (1945a). Publ. Am. Assoc. Advance Sci. No. 22, 1 

 Andervont, H. B. (1945b). J. Natl. Cancer Inst. 5, 391. 



