982 



ADVENTURES IN RADIOISOTOPE RESEARCH 



making use of radio-phosphorus/**) Here we refer to the first turnover 

 studies of body constituents with the help of a radioactive tracer, which 

 were carried out simultaneously with the above-mentioned first investi- 

 gations by ScHOENHEiMER and Rittenberg, who used deuterium as 

 an indicator. 



Blood-plasma phosphate was found to interchange very rapidly with 

 the uppermost phosphate layer of the apatite-like crystallites. This rapid 

 interchange is followed by a slower one due to a slow recrystallization 



Epiphysis 



days 



Fjci, 4. _ Extent of replacement of rabbit's bone phosphorus by 

 labelled phosphorus (reproduced, with permission, from Biochem. J. 



34, 532 (1940) 



of the apatite crystals. Some molecular layers go into solution while 

 others are formed with the participation of labelled phosphate. Such 

 layers will be comparatively strongly active in the early phase of the 

 experiment. Owing to the decrease in the ^^p content of the plasma 

 and lymph with time, they will be much less active in later phases. 

 On top of a strongly active layer, slightly active layers may be deposit- 

 ed, protecting the first layer from dissolution. The great complexity of 

 32P distribution in the skeleton apatite frustrates, or at least makes 

 extremely difficult, a quantitative determination of the extent of renewal 

 of the mineral constituents of the bone when labelled phosphate is admi- 

 nistered only at the start of the experiment. We arrive at such a result 

 when administering daily repetitions of labelled phosphate, thus keeping 

 the level of plasma activity constant. By applying this technique, which 

 is much less convenient, and by comparing the specific activities of the 

 bone inorganic P and plasma inorganic P at the end of the experiment, 

 we obtain a figure indicating the percentage of the renewed skeleton. 

 Results obtained with rabbits, seen in Fig. 4, show that after the lapse 



^**^ Chievitz and Hevesy, Nature 136, 754 (1935). 



