[Ultradian fluctuations in the natural antitumor resistance of mice undergoing transplantation and chemical carcinogenesis].

A study was made of the mouse life span in relation to the time of tumor cell injection on an hourly basis, while the carcinogenic effect was studied in relation to the time of urethan injection. Changes in both the values were shown to vary with ultradian rhythms. It was found that natural killer cell activity against tumor cells, migration index of normal spleen cells in the presence of tumor cells and the activity of carcinogen-metabolising enzyme system of intact animals also exhibited ultradian oscillations.

[Change in the sensitivity to methotrexate of neoplastic cells cultivated in the presence of folic acid].

Cultivation of tumour L-cells in the presence of increasing folic acid concentrations led to the rise in the resistance of these cells population to metotrexate. With the subsequent cultivation, when the folic acid concentration was not increased the population of such cells became more sensitive to metotrexate even in comparison with the initial L-cells.