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The influence of immunological and genetic factors on the appearance of experimental tumors has been studied in mice by means of bidirectional selection. We found that the incidence of lymphomas, solid tumors and chronic nephritis is greater in mice selected for low antibody response than in mice selected for high antibody response. These findings suggest that the genes that control the antibody response also regulate life-span and resistance to neoplastic and inflammatory diseases. Similarly, we are carrying out bidirectional selective breeding to obtain two lines of mice, one sensitive and one resistant to the induction of cutaneous papillomas by chemical carcinogens. The two lines differ notably in terms of both percent of incidence and tumor multiplicity. The results of this study demonstrate clearly that resistance and susceptibility to carcinogenesis are subject to polygenic control.

The extent of osteocytic osteoplasia has been studied in laying hens fed for seven days a hypocalcaemic diet and returned to the commercial laying ratio. The microscopic examination of the femur shows the presence of newly formed bone matrix on the wall of osteocytic lacunae, much more numerous in the experimental animals than in the controls. The physiological significance of the finding is briefly discussed.