192 



G. D. McPherson: Estimation of the 24 Hour Exchangeable Calcium Pool 



specific activity appeared to fall on a straight line during the period from 24 to 

 120 hours as shown in Fig. 2. The '^^Ca specific activity at 24 hours was considered to 

 represent that of the exchangeable calcium pool. The values for specific activity 

 between 24 and 120 hours were treated by least squares analysis to derive an equa- 

 tion representing the decline during this period. The reciprocal of the 24 hour 

 specific activity represented the exchangeable calcium pool in Gms. In the 10 cases 

 studied, the 24 hour exchangeable pool was 9.34 + 2.29 Gms or 307 + 95 mg/Kg ideal 

 body weight. See Table 2 and Fig. 3. 



Table 2. Estimation of 24 hour exchangeable calcium pool in children using *^Ca 



Case 

 No. 



H-3 



H-4 



H-5 



H-6 



H-7 



H-8 



H-9 



H-10 



H-11 



H-12 



24 hour 

 Specific 

 Activity 

 (% dose 

 ^8Ca/Gm. C'a) 



24 hour 

 Exchangeable 

 Ca Pool (Gm) 



24 hour 



Ca Pool (mg.) 



Ideal Weight 



(kg.) 



10.5 



15.9 



8.6 



8.4 



8.8 



10.8 



12.5 



16.1 



15.8 



7.8 



Mean ± S.D. (11.5 ± 3.34) (9.34 ± 2.29) (307 ± 95) 



^ 7 normal infants C'Ca) 

 440mg/kg (Hoffenberg, 1964) 



24 HOUR EXCHANGEABLE CALCIUM 

 POOL 



6 girls, 4 boys ( Calages 7-25-12-6 



307 + 95 mg /kg ideal weight (295 ± 73 mg /kg actual weight) 



(McPherson, 1965) 



8 boys ("'calages 11-2-15-7 

 291 ± 54mg/kg ideal weight 

 (Bronner etal, 1956) 



8 normal adults ("'Ca) ages 25-50 

 86.5 + 20mg/kg 

 (Dymling, 1964) 



i 



20 

 Age in years 



Fig. 3 



The abundance levels reached using this relatively small dose of stable tracer were 

 not high enough to permit precise estimation of the loss of tracer in feces. This would, 

 however, be possible using higher doses of a higher enrichment of ■^'^Ca and would 



