[The significance of the radioactive isotope potassium-40 for the normal development of the animal organism].

21-day-old rats subjected to nourishing by KCl (20-30 mg per day) without radioactive isotope 40K. Besides the decrease of 40K content in animal tissue (30-50%) a reducing of body weight was obtained. In the second set of experiments in the lead (9 cm thick) chamber with low (20 times) background radiation the trustworthy decrease of young mouse development was observed under the simultaneous reducing other components of background radiation (radon, products of its disintegration, gamma, beta radiation, cosmic radiation). Possible mechanisms of necessity of 40K natural concentration for the normal development of the animal organism are discussed.