THE TEETH. 627 



not found to be the case. In man, dentinal tubes may occasionally be seen to 

 enter the enamel, passing across the boundary between the two tissues, and 

 pursuing their course without being lost in irregular cavities." On dentine : 

 ' Each dentinal tube runs outward in a direction generally perpendicular to 

 the surface toward the periphery of the dentine, which, however, it does not 

 reach, as it becomes smaller, and breaks up into branches at a little distance 

 beneath the surface of the dentine. The tubes have definite walls, and are 

 not simple channels in the matrix. These walls are composed of something 

 singularly indestructible. Indeed, the walls of the dentinal tubes are so 

 indestructible that they may be demonstrated in fossil teeth, in teeth boiled 

 in caustic alkalies, or in teeth which have been allowed to putrefy. Similarly 

 indestructible tissues are, however, to be met with surrounding the Haversian 

 canals and the lacunae 'of bone. Each canal is occupied by a soft fibril, which 

 is continuous with the odontoblast cells upon the surface of the pulp ; the 

 existence of these soft fibers was first demonstrated by my father. In the 

 dentine, then, we have (1) a matrix permeated by tubes; (2) special walls of 

 these tubes, or dentinal sheaths ; and (3) soft fibrils contained in these tubes, 

 or dentinal fibers. . . . Owing to their breaking up into minute branches, 

 some of the tubes become lost as they approach the surface of the dentine, 

 and apparently end in fine-pointed extremities. Some terminate by anasto- 

 mosing with terminal branches of others, forming loops near to the surface of 

 the dentine ; others terminate far beneath the surface in a similar way. 

 Some tubes pass into the small, interglobular spaces which constitute the 

 'granular layer' described by my father, while others again pass out alto- 

 gether beyond the boundary of the dentine and anastomose with the canali- 

 culi of the lacunae of the cementum. The enamel also may be penetrated by 

 the dentinal tubes, though this, when occurring in the human subject, must 

 be regarded as exceptional and almost pathological in its nature. Of the real 

 nature of the dentinal fibrils some doubts are entertained. . . . Nerves, in 

 the ordinary sense of the word, they are not, and have never been supposed 

 to be. . . . The cementum, in my opinion, is present in a rudimentary condi- 

 tion upon the teeth of man, etc., as Nasmyth's membrane. It consists of a 

 calcified matrix or basal substance, to a slight extent laminated, and lacunae. 

 Many of the lacunae in cementum are connected, by means of their canaliculi, 

 with the terminations in the dentinal tubes ; they, by the same means, freely 

 intercommunicate with one another. In the fresh condition it appears prob- 

 able that the lacunae are filled up by soft matrix." 



Carl Wedl * says : " Isolation of the enamel-fibers may easily be effected by 

 means of dilute hydrochloric acid. The fibers, becoming swollen and varicose, 

 present on the depressed portions an apparent transverse striation, and 

 between the opposing contiguous portions narrow, fissure-like intervals re- 

 main, which have given rise to the view entertained by some investigators 

 that canals are found in the enamel. The junction of the enamel with the 

 dentine is effected by a transparent, irregular, wavy boundary layer, which in 

 some parts is encroached upon by separate dentinal canals, and in others by 

 elongated, cleft-like cavities, of irregular shapes and different dimensions. 

 Into these cavities, which are mostly filled with opaque, amorphous, calcare- 

 ous masses, one or another of the dentinal canals frequently enters. The 

 cement has an organic connection with the periosteum of the root or root- 

 membrane. Sometimes the canaliculi radiate from the bone-corpuscles in 



- " Pathology of the Teeth," 1872. 



