OF DENTAL ENAMEL. 357 



aqueous solution of corrosive sublimate, partially decalcified in a 

 weak solution of chromic and nitric acids, and embedded in 

 paraffin. Sections were stained with a modification of the Ehrlich- 

 Biondi fluid. The appearances were different from anything I had 

 before seen. There was no trace of a prismatic character in the 

 partially decalcified enamel, but instead a faint appearance of fibres 

 running parallel with the inner ends of the ameloblasts, with small 

 globular masses irregularly distributed among them. 



Fibrous Character of Enamel. 



With the suggestions which this specimen gave me, I prepared 

 some extremely thin sections from the persistently growing incisor 

 of the rat. The enamel rods in the enamel of the rat, as is well 

 known to those who have studied the subject, terminate a little 

 below the surface, leaving on the outside a thin layer of clear and 

 apparently structureless enamel. A partial decalcification of this 

 layer showed a stroma composed of two sets of fibres running in 

 nearly opposite directions, neither direction corresponding with 

 the long axis of the ameloblasts. One set of fibres passes in a 

 somewhat more oblique course than the other, and becomes con- 

 fluent with the ends of the enamel prisms. The other set of fibres 

 sweeps downward on a circular course, crossing the more oblique- 

 running fibres and the enamel prisms nearly at right angles. 

 Sometimes both sets of fibres join, and, twisting about each other 

 in a rope-like design, pass along the course of the enamel prisms 

 (Fig. i). It is probable that the arrangement of fibres is fairly 

 constant in teeth of the same animals, although differing widely 

 in teeth of different animals ; but it is only by cutting sections in 

 a great variety of directions that one at last gets a true picture of 

 the complex arrangement of fibres and rods. Enamel from the 

 teeth of rats and mice shows a more marked fibrous character 

 than any other that I have examined, and the most striking feature 

 of arrangement of the fibre is the interlacing or weaving together 

 of those running in different directions, like warp and woof in a 

 web. This is very plainly shown in Fig. 2, where the torn edge 

 of the enamel bears a striking resemblance to the effect produced 

 by tearing a woven fabric of any sort. 



