EXCHANGE OF PHOSPHORUS IX TEETH 187 



formation was observed on ignition. While important inlbrmation imiy 

 be obtained by the study of X-ray diagrams the interpretation of the 

 latter must l)e made with care. 



PHOSPHORUS EXCHANGE IN THE ENAMEL 



In view of the connection found between tlie content of organic matter 

 and phosphorus exchange in the teeth it did not appear very promising 

 to look for a pronounced exchange in the enamel. The enamel investig- 

 ated by us was in some cases removed mechanically while in others 

 we succeeded in separating the enamel of cat teeth after igniting the 

 tooth very carefully. The enamel, having a different expansion coeffi- 

 cient from the dentine, splits off during the ignition process and 

 can thus be removed. The method of separation used recently by 

 various workers^, in which the tooth is pulverized and placed in 

 an organic liquid of suitable density when the heavier enamel settles 

 to the bottom of the tube, is not suitable for our purpose. The 

 reason is that some dentine often sticks on the pulverized enamel; 

 assuming that the dentine is strongly active and the enamel not, we 

 see that the presence of traces of dentine in the enamel might falsify 

 the analysis. 



We made several experiments with the enamel of cat teeth but in 

 most cases with negative results, the exchange in equal weights of enamel 

 being at least 20 times as small as that found in the molars of cats. 

 In one case we got a positive effect, the canine of a fully grown cat 

 five days after injecting the labelled phosphorus showing a radioactivity 

 of 26 relative units (counts per minute), one enamel sample showing 

 0.6, and another 0.7 counts. The first mentioned enamel was separated 

 by grinding it off from the dentine, while the second one was obtained 

 by the same method from the uppermost enamel layer. The ash weight 

 of the canine was 277.3 and that of the enamel samples 33.1 and 19.1 

 mgm. We are however reluctant to accept this positive result. On account 

 of its smaller weight and greater distance from the underlying dentine, 

 the outermost layer should be less active than the second enamel 

 layer, unless the labelled phosphorus present in the saliva (which 

 13.4 mgm. % P 100 cc.) can interact with the outer layer of the 

 <'namel. We intend to follow up the problem of the phospho- 

 rus exchange in enamel using phosphorus preparations of greater 

 activity. 



^ Comp. P. J. Brekhus and W. O. Arm-strong, J. Dent. Res. 15, 23 (1935). 

 1 M. Karshan, J. Dent. Res. 15, 388 (1936). 



