Defined and repeated alterations in human fibroblasts were discovered under continuous cultivation in the stationary phase. In the normal diploid fibroblast population, two cell subpopulations were distinguished by the heterochromatinization degree of the nucleus. While in the stationary phase, the number of cells with a parahaploid number of large chromocenters, regularly arranged in the nucleus, is seen increasing. It is supposed that the death of the normal diploid fibroblast culture occurs primarily at the expence of cells with heterochromatinized nuclei. Examination of strains with trisomy (47, XY, +7) and of a strain taken from a patient with pigmented xeroderma has shown that the process of nucleus heterochromatinization and its dynamics are substrains. A possibility is discussed of gene or chromosome mutation influences on the well-regulated nuclear heterochromatinization process and on the cell population structure alteration.

Three suspension cell lines from bone marrow (BMPH-1) and spleens (SPH-2 and SPH-3) of hamadryas baboons with haematosarcoma were presented by analogous lymphoid type cells of a high proliferative activity. The modal class of cells in all the three lines was presented by diploids and pseudodiploids, though there was a significant admixture of heterodiploid and subtriploid cells and cells having various types of marker chromosomes. The reconstructed chromosome 1 and satellite chromosomes dominated among the marker chromosomes indicating their relatively greater mutability. No change was observed in Giemsa-banding during a year's cultivation of all three cell lines. The total number of weakly and poorly differentiating chromosomes in aneuploids is more variable compared to the number of well differentiating chromosomes, due, presumably, to a lesser biological significance of the former.

In the experiments with transplacental exposure of mice to N-nitrosoethyl urea (NEU) an enhanced carcinogenesis was noted not only in the first but also in the second generation. This effect in mice of the second generation was manifested in earlier development, as compared with control animals, of different neoplasms as well as in somewhat increased frequency of their detection. Postnatal exposure to NEU would enhance carcinogenesis in mice of both experimental and control groups, whereas no enhancement of carcinogenesis was observed in animals exposed to NEU in progenesis, compared with control mice. Postnatal x-ray irradiation also failed to produce enhanced carcinogenesis, compared with control animals i.e. those exposed to NEU in progenesis. While in female mice of the same group, contrary to the control, ovarian tumors under the effect of irradiation did not arise. It is suggested that there is a pathogenic connection between the inheritance of carcinogenic effect by oocytes and the loss by the ovary its capacity to produce neoplasms in response to irradiation.

The binding between the components of the isolated DNP-complex proved to be more stable in leukemic cells in comparison with the normal lymphoid spleen cells. This conclusion was based on the investigation of the thermomechanical and disaggregation properties of the supramolecular DNP systems isolated from leukemic cells. The change in the isolated DNP-complex were independent of the subpopulation variants of the leukemic lymphatic cells and their chromosome set (diploid or hyperdiploid). The observed changes in the chromatin properties were more specific for leukemic cells than the changes in thechromosome number.

A new cell line derived from transplanted mouse ependimoblastoma consists of typical fibroblast-like cells with well-defined pleomorphism. The line is characterized by a rapid increase and decrease of proliferative activity, by a short stationary phase and early degeneration. The average time of themitotic cycle was determined as being 22-24, tG1-11-12, ts-8-9, tG2-3 and tM-near 0.9 hours. The cytophotometrical evaluation of DNA content revealed two cell subpopulations with different ploidy, both in culture and in tumor in vivo. As compared to the original tumor cells, the cultured cells differ in wider variability of DNA content and a higher average ploidy per nucleus.