. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. KATE OF REJUVENATION OF THE SKELETON i9:i EXPERIMENTS WITH RABBITS After the lapse of 2 hr., 1/530 and 1/1800, respectively, of lh(> tibia epiphysis P and diaphysis P were found to be replaced by plasma P. With incroiising tinie, [\n increase of the replacemont of the l)onc P takes place, as shown in Fig. 2 anrl Table 2; this increase diminishes, however, with inc^reasing lime, as would i)c excepted. The bone tissue contains numerous small crystals formed by mineraliza- tion of the matrix. The crystals are built uj)
. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. KATE OF REJUVENATION OF THE SKELETON i9:i EXPERIMENTS WITH RABBITS After the lapse of 2 hr., 1/530 and 1/1800, respectively, of lh(> tibia epiphysis P and diaphysis P were found to be replaced by plasma P. With incroiising tinie, [\n increase of the replacemont of the l)onc P takes place, as shown in Fig. 2 anrl Table 2; this increase diminishes, however, with inc^reasing lime, as would i)c excepted. The bone tissue contains numerous small crystals formed by mineraliza- tion of the matrix. The crystals are built uj) on similar lines to the mineral apa- tite.^ While the atoms situated on the uppc^-rmost layer of the crystals [Pa- neth. 1922] exchange easily with those present in the surrounding liquid, those situated inside the crystal are prevented from doing so, except at very high tem- peratures. The exchange between bone phosphate and plasma phosphate which we observe in experiments of short duration is due to a replacement process bet- ween the phosphate ions situated on the surface of the apatite crystals and those of the plasma or lymph. Should the surface exchange be exhausted, an increase of the time of the experiment may at first have no effect at all on the extent of replacement. If, however, in the course of time a dissolution and lep- recipitation of the apatite crystals takes place, new and far-reaching possibilities Table 2. Extent of Replacement of the Bone P OF THE Rabbit by Labelled P The labelled phosphate was injected intravenously (luring the experiment Fraction 2 hr. % 4 hr. % Epiphysis 10 20 30 dcys 5C Fig. 2. Extent of replacement of rabbit's bone P by hi belled P 'From X-ray mea-fiirempnt, it was concluded (Caglioti. 193(51 that the inorganic part of the lioiie lias the composition of about 3Ca (l'04)2CjiC03j;H20 with the liejcasonal structure of hydroxyapatite, the length of the axes being a = 9i"2. < \0^* cm. and <? ^
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