Secretion in Cow's Milk of Intravenously Injected Radioactive Phosphorus P32.

Summary Intravenous injection of 15 and 30 millicuries of P32 respectively into 2 lactating cows produced a maximum relative activity per liter of milk of 1.2% of the injected dose at about 5 hours after injection. The relative activity per liter milk is plotted against time after injection and regression equations are presented for interpolating the data. A week after injection, the milk still contains slightly over 0.1% of the injected p32 per liter. Casein with a radioactivity of 2 microcuries per gram was prepared out of milk collected during 3 days after injection of 40 millicuries of P32. A histogram shows the relative rate of P32 secretion in milk. In a week, the 2 cows secreted in their milk 20 and 23% respectively of the injected P32.