228 



ADVEXTUKES IX llADIOISOTOPE RESEARCH 



specific activity data is therefore encumbered with difficulties 

 (cf. p. 221). From data collected during five days, Bauer*'^* estimates, 

 however, that less skeletal calcium than skeletal excess sodium is exchange- 

 able in the rat, thus less than 30 — 40 per cent. As it was shown above 

 (p. 217), the mobilization of some further skeleton calcium is still going 

 on in the mouse after the lapse of more than 100 days and the non- 

 exchangeable part of the skeleton amounts to 67 per cent. 



It is interesting to note that, w^hen injecting ^^fja at the start of the 

 experiment interperitoneally to outgrown rats whose skeletal calcium 

 content was increased appreciably during the experiment, Singer and 

 Armstrong^*^^ found a *^C'a retention of 42—45 per cent in the skeleton 

 after the lapse of 52 days and the release of only small amounts of 

 radiocalcium after that date. Buchanan'^^^\ who exposed mice to air 

 containing ^K!0^, found that 30 per cent of the bone carbonate are 

 replaced within 12 days, while 45 per cent only are renewed in the 

 course of three months. 



b) Conservation of maternal calcium atoms by the offspring through life 



Our results demonstrate the very pronounced ability of the skeleton 

 1o conserve maternal atoms. 



In the first mentioned experiments, one third of the ^^C'a content of the 

 outgrown mouse was found to be replaceable by inactive food calcium. 

 In the latter experiments with growing mice, released "^^Ca had a furthei- 

 outlet, viz. utilization in the formation of additional skeleton, which 

 takes place in the growing organism. 



Investigations were carried out earlier on the loss of ^^p through the 

 lifetime of mice born from active mothers'"''. Some results of these 

 investigations are shown in Table 5. 



Table 5. — Loss of ^^p through the Lifetime 



OF Mice Born from Active Mothers. Mother 



Injected With ^-P on Febri^ary 0. Gestation: 



February 18. Replacement of the Active by 



AN Inactive Mother: Febritary 22. 



* Incl. G" or 3 otTsprinsj 



