PIXC'UANliE Of I'HOSl'HOIUS I.\ TEETIC 173 



increased. All those observations support the hypothesis, that even in 

 fully formed teeth an exehan^c^ of mineral constituents is regularly 

 taking place. To test this hypothesis we have studied the exchange of 

 phosphorus by means of labelled phosphorus atoms. 



PHOSPHORUS EXCHANGE IN TEETH 



We investigated the movement of the phosphorus atoms both in the 

 teeth of fully grown and growing animals by using labelled phosphorus 

 atoms as an indicator. By adding radioactive phosphorus, ])reparcd 

 from sulphur by the action of neutrons, to food administered to animals 

 at a known date, it is possible to distinguish the phosphorus atoms 

 which were present in the food sample and which have been retained 

 and deposited in the organism, from those already present in the body 

 and the teeth at the start of the experiment. We can thus follow the 

 movement of the phosphorus atoms taken in for example a glass of 

 milk and investigate if and to what extent these particular atoms get 

 into the teeth and how they are distributed there. 



The dentine contains 14% and the enamel 17.5% of phosphorus in 

 the form of phosphate (PO^). it is the movement of these phosphate 

 radicles which we actually investigate. For the sake of brevity we shall 

 often use the word phosphorus in discussing the behaviour of the phos- 

 phate radicle. We may recall that the phosphorus taken with food, 

 amounting in the case of an adult to somewhat more than 1 gm. per 

 day, is to a large extent (in most cases up to about 80%) absorbed from 

 the gut and gets into the blood stream. Adult human blood contains 

 44—50 mgm% of phosphorus of which only 2 — 5 mgm% are present 

 as inorganic P. Very different views have been put forward on the for- 

 mation of the l)one and tooth tissue, but they all consider the blood 

 plasma as saturated or nearly saturated with calcium phosphate and the 

 precipitation of the latter from the plasma as being of paramount impor- 

 tance for the ossification process. The solubility of calcium phosphate 

 in the plasma is very strongly affected by the presence of proteins, carbo- 

 nate and bicarbonate ions, and possibly also other constituents. It is 

 also dependent on the acidity of the blood, slight changes in which 

 may be sufficient to produce precipitation. It seems very probable that 

 it is not simple calcium phosphate but a complex salt of the apatite 

 type, a solid solution of hydroxide apatite and carbonate apatite, that 

 precipitates. 



In addition to the inorganic phosphate, blood contains a phosphoric 

 ester at a comparatively high concentration which is mainly found in 

 the corpuscles; as it cannot yield phosphate ions by dissociation, this 

 ester does not affect the saturation of the blood with respect to calcium 



