THE TEETH. 625 



from representative writers on odontology, in order to show how the present 

 theories on this subject have been gradually developed. 



I quote from John Hunter*: " Enamel has no marks of being vascular, 

 and of having a circulation of fluids ; it takes no tinge from feeding with 

 madder, even in the youngest animals. This looks as if the enamel were 

 the earth more fully depurated, or strained off from the common juices 

 in such a manner as not to allow the gross particles of madder to pass. 

 The other substance of which a tooth is composed is bony, but much harder 

 than the most compact part of bones in general." 



Joseph Foxt says : " The enamel, when broken, appears to be composed of 

 a great number of small fibers, all of which are so arranged as to pass in a 

 direction from the center to the circumference of the tooth, or to form a sort 

 of radii round the body of the tooth. This is the crystallized form it acquires 

 some time after its deposit. The structure of the teeth is similar to that of 

 any other bone, and differs only in having a covering, which is called enamel, 

 for the exposed surface, and in the bony part being more dense." 



Thomas Belli maintains: " There are two distinct substances which enter 

 into the composition of the teeth, essentially differing from each other in 

 structure as well as in chemical composition ; the one being organized, the 

 other crystalline. The first, of which the mass of the tooth consists, is true 

 bone ; the second, from its appearance, is called enamel." 



Alexander Nasmyth on cementum says : ' l The cortical substance is always 

 found on the peripheral part of the tooth, forming a layer of investment around 

 it, and lying in close apposition with the enamel or ivory. The cortical sub- 

 stance has no organic connection with the enamel or ivory against which it 

 lies, and, being softer than both, is easily detached by means of a knife. In its 

 intimate structure it presents the characteristic corpuscles and canals of bone, 

 the latter being filled with ossific matter, but otherwise resembling Haversian 

 canals. In structure, enamel is composed of cells which are arranged in regular 

 rows, forming composite fibers placed at nearly right angles to the surface of 

 the ivory, the original nuclei of the cells not being persistent. Dentine. It 

 has long been known that the teeth are composed of two essential chemical 

 constituents, namely, earthy salts and animal matter. From Dr. Thomson's 

 analysis it appears that the quantity of animal matter is very considerable, 

 and it is evident that it is contained chiefly in the fibers, or, as they have 

 been termed, the tubes of the ivory. It was quite evident to me, from the 

 examination of preparations, that the so-called tube was in reality a solid 

 fiber, composed of a series of little masses succeeding each other in a linear 

 direction, like so many beads collected on a string." 



Richard Owen, || in describing the structure of dentine, says : " The 

 compartments of the basal substance, which I have called ' calcigerous,' or 

 ' dentinal cells,' and which contain the hardening salts in their densest 

 state, are sub-circular or sub-hexagonal. The calcigerous and nutrient tubes, 

 varying from 1-1 0,000th to 1-20, 000th of an inch in diameter, are placed 

 with intervals equal to from two to six of their own diameters. They are 

 nearly parallel to one another, both in their general course and curvatures, 



* ' The Natural History of the Human Teeth," etc., 1778. 



t ' The Natural History arid Diseases of the Human Teeth," 1814. 



t ' Anatomy, Physiology, and Diseases of the Teeth," 1831. 



4 ' Researches on the Development, Structure, and Diseases of the Teeth," 1849. 



|| ' Odontography," 1840-45 (vol. i., pp. 302, 303, and 304). 



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