Studies of the mechanism of enhancement by accelerant factor (s) of a transplantable mouse tumor Z8352.

source of accelerant factors, (b) the route of injec tion of accelerant material, (c) the time interval between the administration of accelerant material and the challenge transplantation of cancer cells, (d) the size of the challenge inoculum, and (e) in bred strains of mice, homologous as well as heterologous, as experimental hosts. Noncancerous mouse tissues as a source of ac celerantfactora.—Inasmuch as previous investiga tions (11, 1@) demonstrated the unequivocal re covery of Z8S5@ tumor-accelerant factors from cancerous tissue, attempts were made to deter mine whether noncancerous tissues of mouse origin would also yield such enhancive factors. Because of their inherent physiological and histological similarities with carcinomatous mammary tissue, embryonic tissue and noncancerous mammary glandular tissue were selected for testing. Saline homogenates of the noncancerous tissues (S ml. of 0.85 per cent NaCI solution per gram of minced tissue) were employed as preparatory inocula. The homogenates were prepared from (a) whole em bryos which were obtained by Caesarian section from an AxZbF1 female in its 14th day of gesta tion, (b) lactating mammary gland (containing the mammary tumor virus) secured from AZF@ fe males, and (c) lactating mammary gland (lacking the mammary tumor virus) obtained from AxZbF1 females. The homogenates were assessed for tumor-enhancive activity by injection into ZBC mice, O.@ml. each, of the material under test, followed 10 days later by the challenge of the recipients with 0.1 ml. of a 5 per cent suspension of viable Z8Sà ́@cancer cells. Table 1 presents the re suits of two series of experiments. The first series involves a comparison of the tumor-enhancive ac. tivities of embryonic tissue homogenates and fresh accelerant material; in the second series a comparison is made of the activities (a) of fresh accelerant, (b) of a noncancerous mammary glan dular tissue homogenate which contains mam mary tumor virus, and (c) of a similar homogenate prepared from mammary tissue which lacks the Enhancement in the neoplastic process, as evi denced by a decrease in longevity following chal lenge injection of viable tumor cells, is evoked by pretreatment of recipient test mice with “fresh accelerant― material derived from mouse mam mary carcinoma Z835@ (11, 1@). The previous pa per (1@)described physicochemical and serological characteristics of the accelerant factor(s) . The ex periments described in this paper were conducted in an attempt to elucidate the biological mecha nism of the tumor-enhancive phenomenon.