178 



ADVEXTUEES IN RADIOISOTOPE RESEARCH 



In seeking an explanation of the presence of labelled phosphorus at a 

 very considerable distance from the pulp avc must remember that even 

 the most remote incisal part of the tooth contains organic constituents. 

 The constituents of the blood plasma penetrate through the latter and 

 exchange of phosphate radicles and possibly also some ossification occurs 

 in situ, though only to a modest extent on account of the poor circulation 

 in comparison with that in the vicinity of the pulp. For part V (Fig. 2) 

 we found a loss of weight on ignition amounting to 25% of the 

 weight of the tissue dried in a vacuum dessicator; part I lost 29.8%; 

 and the average loss in ignition was found to be 27.4%. That bones 

 rich in organic constituents, i. e. such in which a comparatively 

 effective circulation takes place, take up more radioactive phosphorus 

 than the diaphysic bones poor in organic constituents had already 

 been found previously in our investigations and is also to be seen 

 in an example discussed on page 178. 



PHOSPHORUS EXCHANGE IN GROWING RATS. 



It is tempting to explain the parallelism between the abundance of 

 organic substance present in the tissue investigated and the percentage 

 of labelled phosphorus present by assuming that the latter is chiefly 

 present in the organic substance and not in the calcium phosphate 

 of the bone or teeth. This possibility must however be discarded because 

 blood weighing as much as an incisor contains after the lapse of few 

 days less than 0.01% of the labelled phosphorus taken, while that found 

 in the incisors exceeds 1%. In view of the importance of this point we 

 tested the effect of the removal of the pulp on the exchange data. The 

 experiment was carried out on a young rat which increased in weight 

 from 87 to 110 gm in the course of the 5 days which elapsed between 

 the subcutaneous administration of the labelled phosphorus and the kiUing 

 of the animal. Before the analysis the pulp was removed from the two 

 upper incisors and the activity of these incisors compared with that 

 of the two lower incisors containing the pulp: we also measured the 

 activity of the extracted pulp. The results are seen in Table 10. 



Table 10. 



Lower Incisoi-s -|- pulp 

 Upper Incisors — pulp 

 Tibia 



Fresh we i slit 



Ash weight 



58.2 



33.2 



800.1 



% of the labelled 

 V found per 

 mgm ash 



37.7 



22.9 



123.2 



0.0192 

 0.0185 

 0.0234 



Loss of weight 

 on ignition 



35.2<% 

 31.0% 



84.6% 



