The effect of cornin, extracted from the skeletal muscle of rabbit was studied in vivo. The results are summarized as follows: 1) Muscle cornin was shown to make sufficient antitumor effects on transpanted mammary tumores of mice.
2) Little elevation of antibody tittes was noted in serum of sabbit. 3) Anaphylactic effects of cornin were relieved by adrenalin. 4) Injection of cornin for long time showed no peculiar effect on mice. 5) Antifertilize action of cornin was discussed.