The results of a comparative study upon the transplantable mammalian and avian tumors indicate clearly that the tumor-producing substances of these two species differ greatly in their power of resistance to a variety of chemical and physical agents. Thus the cancer cells of the animals are rendered impotent by the usual desiccation,1 by exposure to X-rays, radium, ultraviolet radiation (1), and by the action of very weak acid or alkaline solutions, and by neutral salts (2). The filtrates of the rat and mouse tumor emulsions do not contain that material, which, when transplanted, gives rise to the tumors.2 On the other hand, the causal agent of certain infectious tumors of fowls which appear to be analogous to, if not identical with certain mammalian tumors, is not destroyed by desiccation (5), nor by glycerination (.5). Furthermore this active agent is filtrable (5). The chicken sarcoma not only survives the destructive actions of physical agents, such as X-rays, radium and ultraviolet radiation (6), but also withstands treatments with acids, alkalies and neutral salts which will be spoken of later. In view of the fact that the active agent of fowl sarcoma is apparently a soluble virus we felt that it would be of interest to determine whether this virus would separate as part of the albumin or globulin fraction, from filtrates of the sarcoma. Since high concentrations of certain neutral salts together with dialysis are used in separating and purifying the protein fractions, it was necessary to test the effect of these agents alone upon the active material of the fowl sarcoma.