Wistar rats, aged 2,5 months, were intraperitoneally inoculated with the cells of three model tumours: Yoshida sarcoma, Morris hepatoma and mammary carcinoma. On the 6^th day after inoculation the phagocytic potential of the neutrophils (in a mixture with yeast cells – Saccharomyces cerevisiae) was evaluated. Simultaneously, the percentage of lymphocytes with nuclei, undergoing the radial segmentation (RS) - spontaneous or induced with oxalate mixture was determined. It was shown that in experimental rats, the change of leukocytes number and proportion change of particular leukocytes forms are accompanied by the weakening of phagocytic potential of the neutrophils. There was also noted an increase of the number of lymphocytes undergoing the spontaneous RS, while the number of the lymphocytes with the RS induced by the oxalates decreased. The results obtained indicate that the leukocytes changes depend in large measure on the tumour progression degree.

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