Originally- published in Acta Fhijfiiol. Scand. 9, 234 (1945) 



23. RATE OF RENEWAL OF THE FISH SKELETON 



(J. Hevesy 

 From the Kristinebergs Biological Station, Sueden 



The phosphorus atoms present in the organism migrate from molecule 

 to molecule and from organ to organ. The rate of migration greatly 

 depends upon the nature of the molecules involved and on the organ 

 in which they are located, the phosphorus atoms finding their most 

 lasting abode in the skeleton. The mineral constituents of the skeleton 

 are located in apatitelike crystallites which have a size of about 10"^ cm. 

 From the phosphate ions present in these crystallites, only those located 

 in the uppermost molecular layer can come into direct contact with 

 the lymp or the plasma and, thus, participate in an interchange with 

 the phosphate present in the plasma (lymph). The replacement of 

 the bulk of the phosphate or other ions present in the apatitelike 

 crystals can only take place by a partial or total dissolution of the 

 crystallite followed by a crystallization process leading to a partial or total 

 formation of new crystallites. This process is made possible by the 

 fact that the concentrations of phosphate and of other constituents 

 of the plasma vary. Intake of food increases the phosphate content 

 of the plasma and the lymph, and so do numerous biochemical pro- 

 cesses leading to an enzymic splitting of organic phosphorus compounds. 

 The plasma phosphate, for example, increases after intense muscular 

 action, though the low phosphate permeability of the muscle cells 

 (Hevesy and Rebbe, 1940) much reduces the exodus of the phosphate 

 ions split off during muscular action. On the other hand, excretion of 

 phosphate acts in the opposite direction, and so do all those numerous 

 biochemical processes in the course of which phosphate becomes incor- 

 porated with organic^ compounds, from which processes the decrease 

 of the phosphate content of the plasma under the action of insulin 

 is possibly the most conspicuous one (cf. Kjerulf-Jensen and Lunds- 

 GAARD, 1943). 



Not only do the phosphate and the equally important calcium con- 

 centrations of the plasma fluctuate, but the same applies to the con- 

 centration of phosphatase and other enzymes regulating the phosphorus 

 metabolism. Such enzymes act on the bone formation not only by 



