JJETENTIO.N Ui' ATOMS OF .MATKllNAL OJUUl.N IN TUE AUlLi WHITE .MOUSE 



21)1 



course ol' three nionlh uboul 1 gniThe lad lliat neailx one half of the 

 maternal phosphorus is retained in the body, in spite of th(^ 

 comparatively large amounts of phosphorus excreted by the mouse 

 in the course oi" 3 months, is due mainly to the protection of a large 

 proportion of the phosphorus of the bones against interchange with the 

 ])hosphorus atoms in circulation. The uppermost atomic layers of the 

 bone apatite crystals interchange easily with the phosphorus atoms 

 of the plasma or the lymph; furthermore, a kind of biological "recrystalli- 

 zation" takes place, i.e. dissolution of some molecular apatite layers 

 foUow'cd by new formation of such layers through crystallization. .\ll 

 these processes, however, do not affect, or affect only at a very slow 

 rate, large parts of the bone apatite which thus retain their P atoms. 

 During the formation of the skeleton, a large proportion of the ^ap 

 atoms present in the organism will find their way into the bone apatite 

 and be fixed there to a very appreciable extent fluring the time of the 

 experiment (3 months) or even for the lifetime of the mouse. 



When comparing the ^^P content of several rats injected simultaneously 

 with labelled phosphate at different dates, it was found (IIevesy 1939) 

 that the ^'^P, in so far as it was not excreted, accumulated to a very 

 large extent in the skeleton. This fact is illustrated by the following 

 ta])le. 



Table 4. — Percentage ^^p Present in the 

 Body FoTJxn ix s^omf Oikiaxs of the Rat 



Furthermore, when comparing the specific activity (activity of 1 

 mgm P) of the bone P with the specific activity of the plasma P of the 

 rabbit in experiments where the activity of the plasma was kept a1 a 

 constant level throughout, it was found (Hevesy et al., 1940 — 2) that 

 70 per cent of the epiphysial P and 93 per cent of the diaphysial P of 

 the tibia remained unchanged after 50 days. These facts illustrate the 

 ability of the skeleton to prevent an interchange of a large part of its 

 P atoms with the P atoms of the plasma, thus preventing an ultima1<> 

 excretion of such atoms. 



As the calcium atoms of the organism are found to a still higher 

 percentage in the skeleton than the phosphorus atoms, the organism 

 may be expected to retain the average calcium atom obtained by birth 



