Radioactivity of Potassium from H U M a N Sources

The purpose of this paper is to present data which have accumulated in our laboratory over several years tending to show that the relative abundance of the naturally radioactive isotope of potassium K 4° in the human body is probably about 2 per cent less than in commercial or "shelf" potassium as supplied in the market. The work was begun on account of the statement of Ernst (1934) based on an inadequate photographic method that K 4° is (relative to K 39) more abundant in living cells. Since the work was begun other papers by Pohlmann (1938), Pohlmann and Netter (1938), Lasnitzki and Oeser (1937), and by A. Lasnitzki (1939) have appeared, all concluding that if K 4° is more abundant in biological potassium the difference is not over 5 per cent. Since more data are desirable to improve the precision of the result it seems worth while to publish our data. Moreover, since our experiments were completed, Lasnitzki and Brewer (1941) have investigated the abundance of K ~ in potassium from various sources and have found it abnormally abundant in bone (including the marrow) and in plasma but normal in other tissues except tumors where it was low. Presumably similar but smaller differences should be found for the radioactive isotope K 4°. In our measurements the K 4° was directly determined but the results are not wholly consistent with these expectations.