NEOPLASTIC ABNORMAL GROWTH 25I 



cancer cells and cancer agent antiserum developed tumor, although 

 nearly all the control animals did so. 



The findings of the two studies just discussed indicate beyond doubt 

 that "mouse cancer cells are antigenically different from normal cells." 

 It is also stated that "the same antiserum will neutralize a virus and 

 inactivate the cancer cells stimulated by that virus." 



The studies of antibody to the milk agent are similar to the prior 

 work of Kidd ( 121 ) on the Brown-Pearce tumor of rabbits, from which 

 no agent causative of cancer can be recovered. Kidd proved that an anti- 

 body which appears in the blood of some rabbits implanted with that 

 tumor or injected with cell-free extracts of it is capable of suppressing 

 the growth of the transplanted tumor cells. It was shown, however, that 

 the growth frequently regressed in animals which had failed to develop 

 antibody and, conversely, rare animals showed progressive growth of 

 the tumor in spite of a high titer of antibody. The sera of hosts in which 

 the growth had regressed did not suppress the subsequent growth of 

 the tumor cells by in vitro contact unless they contained specific anti- 

 body. 



The admirable discussion of Kidd (52) should be consulted as a 

 reference review of the immunological factors concerned with neo- 

 plasms. He calls attention to the evidence that the fate of transplanted 

 tumor cells is controlled by multiple genetic factors which may decrease 

 during successive transplantation. The usual generalization, previously 

 mentioned, is that the transplanted tissues grow if the hosts have anti- 

 gens in common with the tumor cells and regress in hosts lacking the 

 antigens and so developing antibodies. The failure to transmit resistance 

 passively and the profound differences between the solid immunity 

 which follows the regression of transplanted tumor and the transient 

 resistance set up by inoculations of tumor material are striking. 



It is unfortunate that in the studies of rabbit tumors concerned with 

 specific proteins (viruses) the material is of doubtful genetic homoge- 

 neity. The extensive studies of Bittner on the factors which concern 

 the susceptibility of mice to mammary tumors are revealing and should 

 be consulted (122). From these it is concluded that, whereas in the 

 strains of mice studied little or no cancer occurred in the absence of the 

 milk factor, cancer need not occur in its presence unless two other fac- 

 tors, the inherited hormonal influence and the inherited susceptibility, 

 are also present. 



Bittner and Huseby (122) have contributed beautifully controlled 



