38 THE TEETH. 



salts by means of hydrochloric acid, leaves structures which pre- 

 sent the characters of epithelium ; the remains of the prisms 

 readily fall asunder, and do not dissolve on boiling, but break in 

 pieces. 



While the crown of the tooth is covered by enamel, the neck 

 and root are invested with a layer of cement of varying thick- 

 ness. The cement is a substance presenting the greatest resem- 

 blance to bone, and exhibiting the bone-corpuscles or bone- 

 cavities with their prolongations ; it differs, however, from dense 

 bone in the absence of true Haversian canals. 



Histologists have not hitherto succeeded in throwing any great 

 amount of light on the chemical composition of these tissues com- 

 posing the teeth, although Berzelius* and Lassaigne have certainly 

 drawn attention to the essential differences existing in the compo- 

 sition of the dentine and the enamel, and von Bibraf has devoted 

 much attention to the same subject. All that is known regarding 

 the chemical constitution of the teeth and their individual histo- 

 logical parts, we owe almost entirely to these observers. 



The chemical composition of dentine is very similar to that of 

 bone ; the organic matter consists of gelatigenous cartilage, whilst 

 the mineral parts are precisely the same as those occurring in the 

 bones. The quantitative ratio between the organic and inorganic 

 matters in dentine is somewhat varying, approximating very 

 closely in some cases to that occurring in the dense bones ; but in 

 the majority of the small number of cases recorded, the organic sub- 

 stance amounts to about 28-g-. A little fat is always found to be 

 present with the cartilage. The mineral constituents of dentine 

 are identical with those of the dense bones, and occur in nearly the 

 same relative quantities. The quantity of carbonate of lime 

 appears, however, to be more variable here than in the bones ; 

 from 3 to 8 jj- of carbonate of lime have been found with from 65 to 

 67-- of phosphate of lime. Berzelius demonstrated that fluoride 

 of calcium and phosphate of magnesia are also present in the 

 dentine. 



The enamel differs in a chemical point of view from den- 

 tine, for no cartilage can be obtained from it, whilst the amount of 

 the whole organic matter, which, after being treated with acids, 

 appears like a membranous tissue, does not exceed 2'0 or at most 

 6-6f of the dried mass. From 81 to 88 of phosphate of lime, 

 with about 7 or 8% of carbonate, are found in the enamel. We 



* Lehrb. der Chem. Bd. 9, S. 553. (4 Aufl.) 

 f Op. cit. p. 276. 



