98 



ENAMEL OF THE TEETH. 



a. The enamel. 



The enamel consists, according to Purkinje, of square, or, 

 according to Retzius, of hexagonal closely-aggregated prisms, 

 which stand nearly perpendicular upon the surface of the ivory, 

 and pass outwards in a slightly curved direction. It is at first 

 soft, and if some of it be scratched off in that state, we obtain, 

 what Muller has described as needle-shaped bodies pointed at both 

 extremities. According to Purkinje, Raschkow, and Retzius, 

 some organic substance remains after the young enamel has 

 been treated with hydrochloric acid, whilst Berzelius asserts 

 that the enamel of mature teeth does not contain two per 

 cent, of organic matter. For further details I refer the reader 

 to the excellent works of Purkinje, Raschkow and Frank el, 

 and those of Retzius, J. Muller, and v. Linderer 



If an immature tooth of a child or mammal (the pig, for 

 instance) be removed from its capsule and placed in dilute 

 hydrochloric acid, the organic substance of the enamel which 

 remains after the solution of the earthy matter, may be sej^a- 

 rated from the ivory entire. It has exactly the form and size 

 of the enamel previous to the action of the acid. It is very 

 soft, and breaks readily in the direction of the fibres of the 

 enamel. Examined with a high magnifying power and subdued 

 light, it is found to be composed, like the enamel itself, of 

 closely-aggregated prisms, which may be insulated from one 

 another, so that each one forms an independent structure. 

 (See pi. Ill, fig. 3.) This organic substance, therefore, cannot 

 be, as Raschkow and Retzius considered, a mere deposit from 

 the moisture with which the enamel-fibres are at first sur- 

 rounded, and thus a sort of cast of the enamel-fibres, but 

 either the fibres must result from an ossification of these 

 prisms, or the prisms must be hollow, and the inorganic 

 substance deposited within them. When the enamel of the 

 pig's tooth is examined with a subdued light, the contour of 

 tjhese organic prisms is found to be so dark in comparison with 

 their interior, that it can scarcely be regarded as the mere 

 shaded outline of a solid prism, but suggests the idea of a 

 cavity surrounded by a thin membrane. This distinction is, 



