190 ADVEXTURES IX RADIOISOTOPE RESEARCH 



Summary 



It has been shown that an exchange of phosphorus atoms present in the teeth 

 with those present in the blood plasma takes place. 



During the growth of the incisors of rats the newly deposited phosphorus 

 atoms are to a large extent found in close vicinity of the dental pulp, but even in 

 the most remote part of the incisor presence of newly substituted phosphorus 

 atoms can be established. An exchange of phosphorus atoms thus takes place 

 even in those parts of the incisors which are entirely outside the range of the 

 pulp. The exchange in the molars was found to be less pronunced than that 

 in the incisors, this being presumably due to the fact that these do not grow. 



In the teeth of young cats within fews hours., Vjesides an exchange of phos- 

 phorus atoms, an increase in the labelled phosphorus content due to the growth 

 of the teeth could already be ascertained. 



An exchange of phosphorus has also been proved for human teeth, 1 : 300,000 

 of the phosphorus administered being found in each tooth. The replacement of 

 1 "o of f^6 phosphorus content of a human tooth by phosphorus atoms taken 

 up with the food takes about 250 days. 



