176 



ADVENT IRES IX KADIOISOTOI'E KESEAKCH 



In the expeiimeiits now to be described the distal part of tlie incisor 

 was removed l)y operation one day before labelling the phosphorus 

 present in the blood. In these experiments the radioactive P was not 

 added to the food but given in the form of subcutaneous injections. 

 2 days, 5 days and 8 days after the administration of the labelled phos- 

 phorus the end part of the freshly grown incisor was again removed 

 by operation and its radioactivity ascertained. The distal parts removed 

 were all outside the range of the pulp. The figures obtained are seen 

 in Table 7 and those from a similar experiment in Table 8. 



Percentage of the labelled P found in mgm of average incisor tissue 

 = 0.0076. The removed distal ends contained 8 to 25 times less labelled 

 P than the average tissue. 



Table 8. 



Percentage of the labelled P found in 1 mgm of average incisor 

 tissue = 0.0062. The removed distal ends contained 10 to 16 times 

 less labelled P than the average tissue. 



Though the figures in the tables above clearly show that the deposition 

 of labelled phosphorus is not restricted to the regions in the vicinity 

 of the pulp, but that the labelled phosphorus is to be found even in the 

 most remote part of the incisors, we attempted to obtain incisors with 

 an appreciably larger pulp-free part. As is well known, rats, being 

 rodents, grinfl their teeth and thus continually remove parts of th(> 

 pulp-free end of the growing incisors. By eliminating the upper incisors 

 the animal was prevented from gnawing and incisors were thus obtained 

 in which the distal pulp-free end had a length of 10.5 mm. as shown 



