376 



THE MICROSCOPE. 



fig. 178. 



Sections of Human Teeth. 

 1. Vertical Section. 2. Horizontal Section. 



cementum, whilst the substance or body of the tooth is composed of 

 dentine. The enamel is composed of solid prisms or fibres, of about 



l-5500th of an inch in 

 diameter, arranged side 

 by side, and closely adhe- 

 rent to each other.. 



The dentine consists 

 of a fine substance in 

 which mineral matter 

 largely predominates, 

 though to a less degree 

 than in the enamel. It 

 is traversed by a vast 

 number of very fine cy- 

 lindrical, branching, wavy 

 tubuli, which commence 

 at the pulp cavity and 

 radiate towards the sur- 

 face. The cementum cor- 

 responds in all essential particulars with bone, preserving its charac- 

 teristic lacunae, traversed by vascular medullary canals. 



The very interesting structural characters of teeth in some of the 

 lower animals, called forth an able work from the pen of Professor 

 Simon ds, of the Royal Veterinary College : to his book upon this sub- 

 ject we beg to refer the reader. 



Czermak discovered that the curious appearances of globular con- 

 glomerate formations in the substance of dentine, are entirely depend- 

 ent on its mode of calcification ; and he attributes the contour lines to 

 the same cause. Contour markings vary in intensity and number ; 

 they are most abundant in the root, and most marked in the crown. 

 Vertical sections exhibit them the best. In preparing the specimen, 

 first make the section accurately, then decalcify it by submersion in 

 dilute muriatic acid. It should then be dried and mounted in Canada 

 balsam, with continued heat, so as to allow the specimen to soak in the 

 fluid resin for some time before it cools. It is the white opacity of the 

 extremity of the contour markings that produces the appearance of 

 rings on a tooth-fang. 



" The tooth-substance appears," says Czermak, " on its inner sur- 

 face, not as a symmetrical whole, but consisting of balls of various 

 diameter, which are fused together into a mass with one another in dif- 

 ferent degrees, and on which the denterial tubes in contact with the 



