This is to report the results of investigation on the process of milk secretion and the phosphorus metabolism in animal body, by considering the changes of concentration of the radio active phosphorus (P32) in the blood and in the milk, as a function of time. The results are summarized as follows: Radioactive phosphorus was transferred to the blood at nearly the same time after subcutaneous injection of P32 and the maximum radioactivity was encountered within 30 minutes, and thereafter the specific activity regressed gradually. There was a considerable amount of P32 in urine at 2 hours after injection, but not in feces. P32 was transferred to the milk soon after injection. The radioactivity of the milk reached the peak at about 3 hours after injection and the specific activity was higher than that of blood. It seems probable that the alveolus cells may absorb phosphorus selectively. The specific activity of the casein phosphorus was detected at 2 hours after injection. From this, it may besaid that the time of formation of the casein in the gland cells is estimated to be about 2 hours. The peak of specific activity of casein phosphorus preceded considerably that of the organic phosphorus of milk. This considerable delay in the organic milk phosphorus may arise from formation of phospholipid. So it seems probable that the formation of fat involves a longer delay than that of protein formation.1. 皮下注射直後血液中には多量の放射性燐が吸収されるが, しかし骨格並びに組織中の燐との速かなる置換及び細胞間体液への拡散等により急激に血液中から減少する. 同時に体外排泄, 就中尿への排泄は早く, 注射数時間後の尿中にすでに放射性燐が存在した. 2. P32注射後の乳汁中には血液と比較して甚だ多量の放射性燐が存在している事から, 乳腺細胞は鱗を選択吸収するものと考えられる. 3. カゼイン中のP32出現時間及び乳中有機燐の比放射能の時間的推移から, 乳腺のカゼイン生成に要する時間は約2時間であり, 又燐脂質生成は燐蛋白生成よりも遥かに時間を要するものと推定される
