245 



Comment on papers 24, 25, 20 



The availability of ■'^Ca at a later date much facilitated the investigations of 

 processes taking place in the bone apatite. Experiments taking years could be 

 (tarried out, which had not been possible before. Furthermore, in contrast to the 

 body phosphorus, which is only partly found in the skeleton, 99 per cent of the 

 body calcium of the mouse is concentrated in the latter. In paper 24 experiments 

 are described in which ^^Ca was administered to pregnant mice and also to th(^ 

 offsprings until they were fuUy grown. After that date, they were kept on a non-ra- 

 dioactive diet. Mice were then killed at intervals, and the *^Ca content of their skeleton 

 determined. In the coui-se of 2 years, which covers the largest part of the life span of 

 the mouse, 33 per cent of the skeleton ^^Ca, and thus of the skeleton calcium, was 

 found to be replaced by calcium atoms of the food or present formerlj'^ in the soft 

 tissue. When ^^Ca was administered to the pregnant mouse alone, the offspring were 

 found to conserve 50 per cent of the maternal calcium atoms through life. When 

 similar experiments wore carried out with ^-P (paper 20) 60 per cent of the ^^P 

 acquired by the mouse at birth was found to be lost when reaching maturity 

 (paper 23). The calcium atoms have a fairly stable position in the skeleton so 

 that it takes a great number of generations until the last calcium atom originating 

 from the first ancestor is lost. In contrast with calcium atoms, the last ancestoral 

 water molecule is lost already after a few generations, as described in paper 25. 

 The above-mentioned renewal figures indicate replacement of skeleton calcium 

 atoms by such taken up with the food or formerly located in soft tissues. Changes 

 in the apatite crystals without participation of food calcium or soft tissue calcium 

 would not be indicated by the methods described. 



In the course of a symposium which took place in the Ciba Foundation in 1951 , 

 the question was raised of how much chloride is to be found in the mineral consti- 

 tuents of the skeleton. This question, which could not then be answered, induced 

 an investigation the results of which are found stated in paper 26. The non-exchange- 

 able chloride fraction was found to remain very much behind the non-exchange- 

 able sodium fraction of the mineral constituents of the bone. 



