242 ADVENTURES IX RADIOISOTOPE RESEARCH 



If the human hali' of the exchangeable chloride is removed in the 

 course of 14 days^^) and replaced by chloride of the food and after 6 

 months, i.e. after 12 periods, all exchangeable chloride initially present 

 will be practically absent. In the mouse, with its high metabolic rate, 

 the removal rate of chloride can be expected to be still higher than in 

 man. The removal can be accelerated by increased chloride feeding. 

 Besides the chloride present in the standard biscuits fed we added 

 0.2% NaC'l to the water the mice were drinking after they were put 

 on non-radioactive diet. To the water administered to the mice in the 

 first phase of the experiment ^^Cl of 0.67 ju C activity per liter was added 

 as sodium chloride weighing 9.3 mgm. The labelled chloride was adminis- 

 tered to pregnant mice about 2 weeks prior to gestation. After gestation 

 the administration of labelled chloride was continued for 4 months 

 when the animals were fully grown. One member of each litter was then 

 killed and its total ^^C'l content and that of its skeleton determined. 

 The remaining members of the litters were investigated 6 months later. 



The bone was ashed in the presence of sodium carbonate. The activity 

 of 100 mgm, thus of an infinite thick layer of the samples obtained was 

 determined, the counts registered being multiplied by the total weight 

 of the ash-sodium carbonate mixture. 



The total ash of the first member of the litter of the mice investigated 

 had a total activity of 2780 counts per min, mean value 2910 i 452 

 counts, that of the the mineral constituens of the skeleton of the first 

 investigated offspring 56.6 counts. This was prior to biological removal 

 of all exchangeable chloride from the skeleton but after the removal 

 of some of the latter in the course of the isolation of the mineral con- 

 stituents. 



By keeping the mice on an activity-free diet for 6 months the activity 

 of the mineral constituents declined in the average to 21.2 counts 

 (cf. Table 1). 



The total chloride content of a 35 gm mouse taken to be 48 mgm, the acti- 

 vity of 1 mgm of the body chloride prior to removal of the active food 

 was 60.6 counts per min. As the total skeleton after biological removal 

 of all exchangeable chloride had an activity of 21.2 counts per min. 

 the sequestered chloride content of the bone mineral amounted to 

 0.35 mgm or 73% of the total body chloride. 



The sequestered fraction of the bone calcium of the mouse, that non- 

 replaceable by circulating calcium, was found^^) to be 67.2 ± 7.9%. 

 The corresponding figure for bone sodium is stated to be 60 — 70('^>, 

 65(4), 60<5) and 69(6) by different authors. Thus about a similar percentage 

 of excess sodium and of excess calcium is prevented from interchanging 

 with their circulating atoms. The sequestration of bone constituents 

 is iresumably due to the fact that a contact between these constituents 

 and the circulating body fluids is obstructed. To arrive at the total 



