226 



ADVENTURES IN EADIOISOTOPE RESEARCH 



^^Ca observed in experiments lasting 100 to 180 days amounts to 43 

 per cent (Table 4). The loss of ^^Ca during the first three days of life 

 is less than 10 per cent; thus half of the maternal calcium atoms are 

 preserved during life. 



100 -rt 



80- 



c 



V 



c 

 o 



u 



o 

 u 



60- 



40- 



20 



~1 — 

 100 



200 



300 



400 



500 



600 



doys 



Fig. 2. Loss of *^Ca, obtained from labelled mother at birth, during 

 lifetime of the mice. Each point indicates the ^^Ca content of another member 



of the litter killed at the stated time 



The calcium content of our newly born mice, weighing 1.23 — 1.37 

 gm. varied between 0.28 and 0.35 per cent of the body weight, not 

 much differing from the calcium content of the new-born rat (4.7 gm) 

 for which data varying between 0.27 and 0.35 per cent are reported*^^^\ 

 The calcium content of 1 gm fresh weight of newly born mouse amounts 

 to 0.3 times that of 1 gm of the adult animal, which is 1.05 per cent. 

 If all the maternal calcium atoms had the same chances to supply cal- 

 cium to the offspring, and all were labelled, we would find 1 gm of 

 newly born mouse to be 0.3 times as active as 1 gm of the mother. 

 We find the ^^Ca content of 1 gm of new-born mouse to amount to 1.7 

 times that of 1 gm of the adult mouse. The ^^Ca taken in by the mother 

 has thus only an opportunity of interchanging in the average with 

 about 1/5 to i/e of ^^^^ body calcium before being utilized in the building 

 up of the embryo. 



