THEIR CHEMICAL RELATIONS. 39 



have already spoken of the abundance of fluoride of calcium pre- 

 sent in the enamel. (See vol. i, p. 424.) The chemical investiga- 

 tions of this substance have left it undecided whether the phos- 

 phoric acid and lime enter into a different combination in the 

 enamel and dentine from that occurring in the bones. 



Although the cement of the teeth has been most imperfectly 

 examined, yet von Bibra, Lassaigne, and Marchand concur in 

 regarding this substance as more analogous in its composition to 

 bone than dentine was found to be ; it differs from the latter in 

 containing a little more organic matter. 



Lassaigne and von Bibra found on a average a rather larger 

 quantity of mineral substances in the molars than in the incisors. 



It would appear from observations made by Lassaigne, that the 

 organic matter diminishes with age in the teeth as well as in the 

 bones. 



The comparative experiments of Lassaigne and von Bibra on 

 the teeth of different animals have yielded very few results which 

 would justify the establishment of general propositions; the last 

 named of these observers could not even discover any definite 

 difference in the composition of the teeth of carnivorous and her- 

 bivorous animals. Bibra' s observations show that there is a strik- 

 ing relative excess of organic matter in the grinders of the elephant 

 and the wild boar, and that the teeth of these pachydermata contain 

 a very considerable quantity of phosphate of magnesia (as much, 

 according to him, as from 6 to 12--). 



Carious teeth do not very readily admit of chemical investiga- 

 tion ; but it may be observed that, according to Marchand, the 

 tendency of the teeth to this mode of destruction may be referred 

 to their containing an excess of carbonate of lime. 



The remarks already made concerning the analysis of the bones 

 refer equally to that of the teeth ; excepting only that it is more 

 difficult to prepare the materials for examination in the latter case, 

 more especially in exhibiting pure enamel or cement; the best 

 method of obtaining the former of these substance is by heating 

 the tooth to a few degrees above 100, when one portion of the 

 enamel becomes spontaneously detached, and the removal of adja- 

 cent pieces by mechanical means can be then readily effected. 

 These detached portions require, however, still further cleaning to 

 remove the tissue of the dentine which may be attached to them. 

 In consequence of the difficulty of drying the enamel thoroughly 

 when in masses, von Bibra's method should be adopted, which 

 consists in pulverising the purified enamel, and then drying it. 



