Originally oommunicated in Acta Chemicfi Scand. 11, 2()1 ( 19.57) 



26. NOTE ON THE CHLORIDE CONTENT OF THE 

 MINERAL CONSTITUENTS OF THE SKELETON 



(J. Hevbsy 



From the I)istitnt for Research in Ojganic Chemistry, Stockholm 



In view of the only slightly differing size of the hydroxyl and fluoride 

 ion, the hydroxyl ions of the bone apatite can be replaced by fluoride 

 ions. Furthermore some of the fluoride may be present in the bone mineral 

 as calcium fluoride. 



The fluoride content of the bone apatite is determined by that of the 

 plasma, which in turn depends on the fluoride content of the food. 

 The fluoride content of the earth's crust is much lower than that of the 

 seawater, the mineral constituents of the skeleton of mammals living 

 in the sea is, correspondingly, very much, about eleven times, larger 

 than that of mammals living on land, which contain about 0.05 % fluoride 

 only. The skeleton of fish living in the Baltic, which has a low fluoride 

 content, have a much lower fluoride percentage (0.06 %) than the ske- 

 leton of fish living in the Atlantic (0.43%). Incorporation of fluoride 

 into the mineral constituents of the bone was in recent years much 

 investigated, mainly in connection with the observation that the presence 

 of fluoride in the mineral constituents of teeth increases their resistance 

 to caries. 



The radius of the chloride ion is much larger (1.81 A) than that of 

 the fluoride ion (1.33 A) and calcium chloride being very soluble we 

 can expect to find slight amounts of chloride in the mineral constituents 

 of the bone. While the X-ray diagram of f luoroapatite is almost identical 

 with that of hydroxy-apatite that is far from being the case for chloro- 

 apatite'^^^ The fluids circulating in the bone tissue having a high chloride 

 content (about 300 mgm/100 ml); this has to be quantitatively removed 

 prior to the determination of the amount of chloride incorporated into 

 the mineral constituents. Such removal by chemical treatment of the 

 bone encounters great difficulties. However, when labelling the skeleton 

 all through with radiochloride and placing the animal, e. g. the mouse, 

 on diet containing non-radioactive chloride for several months, all 

 exchangeable radiochloride will be removed and excreted. Ihe radio- 

 chloride fixed in the mineral constituents alone remaining in liie ske- 

 leton. 



1 6 Hovesy 



