THE DENTAL TISSUES. 75 



demonstrated by the growth of leptothrix having followed 

 them with exactitude. 



It sometimes happens that indications of spherical forms 

 and faintly discernible contours resembling those of the 

 interglobular spaces may be seen in dried sections, in which 

 no actual spaces occur. The appearances are perhaps pro- 

 duced by the formation of an interglobular space, the con- 

 tents of which have subsequently become more or less 

 perfectly calcined ; and the appearance described as " areolar 

 dentine" is probably to be explained in this manner. 



The exact nature of the contents of the interglobular 

 spaces is not very certain : they may, with some difficulty, 

 be tinted by carmine, and it is said that they may, like 

 the dentinal sheaths, be isolated by the destruction of the 

 rest of the matrix in acids ; that this may be done I do 

 not doubt, although I have never succeeded in so isolating 

 them myself. 



Bodecker finds that there is soft living plasm abundantly 

 distributed in the smaller interglobular spaces which con- 

 stitute the granular layer, and that this is in very free com- 

 munication with the soft fibrils in the tubes on the one side, 

 and with the soft contents of the lacunse and canaliculi of 

 the cementum on the other. 



In the dentine so far described, which is that variety known 

 as hard or unvascular dentine, some degree of nutrition is 

 perhaps provided for by the penetration of the whole thick- 

 ness of the tissue by protoplasmic fibres, the dentinal fibrils, 

 but this nutrition may be effected in a different way, and 

 there are other varieties of dentine known in which dentinal 

 fibrils have never been shown to exist. For descriptive 

 purposes I would classify dentines as 

 (i.) Hard or unvascular dentine, 

 (ii.) Plici-dentine. 

 (iii.) Vaso-dentme. 

 (iv.) Osteo-dentine. 



