STRUCTURE OF TEETH; ENAMEL, DENTINE. 



177 



the substance next to be described. The tubuli, in their radiating course, de- 

 scribe two, three, or more curvatures, appreciable by a low magnifying power; 

 these are termed by Prof. Owen, the "primary curvatures." With a higher 

 power, the tubes are seen to be bent, throughout the whole of their flexuous 

 course, into minute and equal oblique undulations, of which 100 may be 

 counted within the space of l-10th of an inch ; these are the "secondary cur- 

 vatures" of Prof. Owen. Both the primary and the secondary curvatures of 

 one tube are usually parallel with those of the contiguous tubes ; and from 

 the radiating course of the tubuli, the rows of curvatures have the appearance 

 of lines running parallel with the external contour of the tooth. The dia- 

 meter of the tubuli in their largest part averages about 1-10, 000th of an inch ; 

 their smallest branches are immeasurably fine. It is impossible that they 

 can receive blood; but it may be surmised that, like the canaliculi of bone, 

 they absorb matter from the vascular lining of the pulp-cavity, which aids in 

 the nutrition of the tooth. Although, when once fully formed, the Tooth un- 

 dergoes little or no change, there is evidence that it possesses a certain power 

 of repairing the effects of disease ; a new layer of hard matter being some- 

 times thrown out on a surface, which has been laid bare by Caries. It has 

 been found, too, that the Dentine is sometimes tinged by colouring matters 

 contained in the blood. This is most evident, when a young animal is fed 

 upon madder, during the period of the formation of the tooth ; but even in an 

 adult, some tinge will result from a prolonged use of this substance; and it 

 has been noticed that the teeth of persons, who have long suffered from Jaun- 



[Fig. 80. 



Fig. 81. 



Transverse sections of tubules of dentine, 

 showing their cavities, their walls, and the 

 intertubular tissue. 



a. Ordinary distance apart. 



b. More crowded. 

 e. Another view. 



Human molar. Magnified 400 diameters.] 



Oblique section of Dentine of human 

 tooth, highly magnified, showing the calci- 

 gerous tubuli, and the outlines of the original 

 cells. 



dice, sometimes acquire a tinge of bile. Attention has been particularly di- 

 rected by Prof. Owen, to appearances which he regards as indicating the 



