Copenhagen

The active phosphorus content of the urine and faeces shows great fluctuations during the first few days after the intake of the preparation. Later, it becomes fairly constant; and we have obviously to deal with the excretion of phosphorus which has already been deposited for a while in the skeleton, the muscles, or other organs, and which has been displaced again. From our experiments, it follows that the average time which a phosphorus atom thus spends in the organism of a normally fed rat is about two months. This is also supported by the fact that rats killed about a month after the intake of phos phorus contain only about half the active phosphorus found in those killed after a week's time. This result strongly supports the view that the formation of the bones is a dynamic process, the bone continuously taking up phosphorus atoms which are partly or wholly lost again, and are replaced by other phos phorus atoms. In the case of an adult rat, about 30 per cent of the phosphorus atoms deposited in the skeleton were removed in the course of twenty days. In another set of experiments we investigated the different parts of the skeleton. No conspicuous dif ferences in the active phosphorus content could be found, with the exception of the teeth. The front teeth, which grow rapidly in rats, contained a larger part of the 2 mgm. phosphorus taken than the aver age of the whole skeleton, the ratio being about 10:1 in the case of adult and 6:1 in that of half-adult rats, whereas the molar teeth took up less than the average per gram of the skeleton, the ratio being 1:2 in the most extreme case. A detailed account of these and further results will be published elsewhere. We wish to express our thanks to Prof. Niels Bohr for the kind interest he has taken in this work. For the preparation of the radioactive sources, and help ful assistance in making the measurements, we woul