THE TEETH. 



623 



In some places, especially on the cusps, the spindle-shaped enlargements of 

 the dentine-fibers are quite numerous, and of an almost uniform size and 

 direction, forming regular rows of spindles within the enamel. In the teeth 

 of younger individuals the spindle-shaped enlargements are comparatively 

 larger and more regular than in the teeth of old people. 



The boundary line between the dentine and enamel is either straight or 

 slightly wavy, and with more or less deep, bay-like excavations, analogous to 

 those on the boundary between dentine and cementum. The concavities of 

 the bays are directed toward the dentine. In this interzonal layer at the bot- 

 tom of the bays we meet with fibers occupying the curved spaces between 

 dentine and enamel, or we see, in a correspondingly bent direction, bioplasson 

 bodies directly connected with the dentinal fibers downward, and with the 

 enamel fibers upward. (See Fig. 270.) In specimens stained with chloride of 



E F 



FIG. 269. UNION OF DENTINE WITH ENAMEL. 



Z>, dentine; E, enamel; DF, dentinal fibers, being in union with large bioplasson bodies, 

 P, or directly running into enamel-fibers, EF ; the latter often are lost in the delicate, irregu- 

 lar net- work on the bottom of the enamel. Magnified 1200 diameters. 



I 



gold the dentine is always much deeper in color than the enamel, hence the 

 relations described are very plainly marked on such specimens. 



Results. The details described make it evident that we shall have to mod- 

 ify considerably the views heretofore maintained on the structure of the 

 teeth. Since we have known the structure of " protoplasm," and that of 

 basis-substance of connective tissue, by the researches of C. Heitzmann, we 

 are accustomed to. look for the distribution of the living matter not only in 

 the plastids (the formerly so-called cells), but also in the basis-substance, 

 which formerly was thought to be devoid of life. 



The structure of the tooth closely resembles that of bone. We know that 

 the basis-substance of bone is traversed everywhere by a net-work of living 



