102 PURKINJE AND MULLER ON THE TEETH. 



The enamel and ivory of the teeth are the most indestructible 

 after death of all parts of the body. In opening tumuli or other 

 ancient places of sepulchre, they are frequently found to have 

 undergone scarcely any decomposition. 



The cortical substance or cementum, see Fig. 24, consists of a 

 thin osseous layer developed on the external part of the fangs, 

 down to the orifices which lead to the cavity of the tooth. It is 

 essentially of the same structure as true bone, containing the 

 characteristic corpuscles, and calcigerous branching tubuli of 

 that tissue. It is supposed to be formed by ossification of the 

 capsule in contact with the fang, and is certainly the seat of the 

 exostosis often met with on the roots of the teeth. In old age it 

 makes its appearance in the cavity of the tooth, and is formed 

 from the membrane of the pulp the pulp shrinking and retiring 

 in proportion as the cement accumulates. 



The chemical composition of the two substances of the hu- 

 man teeth, consists, according to Berzelius, in the hundred 

 parts, of 



Enamel. Bone. 



Animal matter, - 20.0 



Phosphate of lime, with fluate of lime, 88.5 - 64.3 



Carbonate of lime, 8.0 - 5.3 



Phosphate of magnesia, - 1.5-1.0 

 Soda, with some chloride of soda, - 1.4 



Free alkali and animal matter, 2.0 



100.0 100.0 



Purkinje and Miiller, have recently, with the aid of the 

 microscope, investigated very minutely, the structure of the 

 teeth, and their discoveries have been confirmed by many 

 other observers of high reputation. They describe the bony 

 part of the tooth as consisting of fibres running parallel to each 

 other from the external to the internal surface of the tooth, 

 between which is placed a semi-transparent, homogeneous por- 

 tion. These fibres they believed to be really tubular; for on 



