180 



AUVEXTURES IX llADIUISOTOl'K llESEARCH 



Table 12. 



Weight of the 



fresh tissue in 



mgm 



^\'eigl»t of 

 ash in mgm 



% i>f the labelled 



I* found per mgm 



ash 



A I 131.1 



B 312.4 



C 243.8 



0.0080 

 0.002() 

 0.0027 



in the course of 7 days only to a small extent. The figures in Table 

 12 cannot be compared directly with those obtained from fully grown 

 animals for the following reason: the growing animal being much smaller 

 the percentage of labelled P obtained for the same weight of the organ 

 becomes larger; furthermore growth much facilitates the uptake of 

 phosphorus. We can, however, compare the ratio of the labelled P 

 content of the incisor and of other organs; the value of this ratio for 

 the tibia, for example, is found to be not appreciably different in the 

 cases discussed above. As to the labelled phosphorus content of the 

 blood, this amounted after the animal was killed to only 0.04% per 

 gram of blood; assuming a blood content of 10 cc. the circulation 

 contained but 0.4% of the labelled phosphorus administered of 5 days. 



THE EXCHANGE OF LABELLED PHOSPHORUS IN MOLARS 



In contrast to the incisors, molars of adult rats do not grow, so the 

 labelled phosphorus found in the latter is due solely to exchange pro- 

 cesses; the blood stream circulating through the molar carries labelled 

 phosphate ions which enter into exchange processes with the calcium 

 phosphate of the molar tissue. Such exchange processes also take place 

 in the incisors simultaneously with the formation of new ossification 

 })roducts. In the molars of adult animals, however, we encounter chiefly 

 the former process; but though growth can be excluded we cannot 

 discard the possibility of dissolution of tooth tissue at one place and 

 a corresponding precipitation of calcium phosphate at another along 

 the boundary between the circulating fluid and the tooth tissue. Small 

 fluctuations in the acidity or parathormone concentration of the blood 

 are sufficient to cause such a process. The molars of the rat decribed 

 on p. 181 showed a content of labelled phosphorus amounting to 0.0013% 

 per mgm of tissue and 0.0018% per mgm of ash, which is less than in 

 the average incisor. The loss on ignition was found to be 26.9%. We 

 thought furthermore that it would be of interest to compare the labelled 

 P content of the incisors, molars and skeleton, choosing the tibia as 

 representative of the latter. The figures obtained are seen in Table 13. 



