“…It is well known, however, that body fluids having a direct, injurious action on heterografts may be demonstrated by the methods of tissue culture (Harris, 1943). As Harris reminds us, earlier workers in cancer research (Lambert and Hanes, 1911;Lumsden et al, 1934) were interested in cytotoxins as a possible antiserum against tumor cells, rather than in their significance as a factor in the transplantation of tissues. Subsequent work has not, as yet, substantiated the hopes of these workers.…”