TISSUES OF THE BODY. 273 



REMARKS. 1. Here we meet with two different views, as in considering hone and 

 connective-tissue. According to one of these, dentine arises from the odontoblasts in 

 the form of an intercellular substance produced by the latter; according to another, a 

 direct calcification of these cells takes place. The latter theory has been defended 

 recently, principally by Waldeyer : " The formation of dentine consists in a trans- 

 formation of part of the protoplasm of the ivory cells into a glutinous substance, 

 which becomes subsequently calcified, after which the other unchanged part of the 

 body of the cell remains over in the hardened mass in the form of soft fibres." 2. 

 Besides diffuse calcification, the laying down of the dentine globules takes place at 

 this period. These are small spheroidal calcified bodies, which are supposed to be 

 partly permanent (p. 262), and partly to disappear subsequently. Hoppe maintains 

 that they are not simple concretions of the bony earths with an organic collagenic 

 substratum, as has been already mentioned. He was unable to convert their organic 

 substratum into glutin by boiling. He is rather of the opinion of Hannover, that 

 their nature is cellular. In the interstices incompletely calcified appearing between 

 them, again we have the " interglobular spaces" touched on in section 150. 3. 

 See Trans. oftheLorulon Pathol. Society, vol. vii., p. 185. Earlier numbers also of 

 this periodical contain other important works of the same author on the diseased 

 states of the teeth. 



D. Tissues composed of Transformed and as a rule Co- 

 hering Cells, with homogenous, scanty, and more or 

 less solid Intermediate Substance. 



12. Enamel Tissue. 

 156. 



Enamel, which in the human subject is confined to the teeth, as also 

 among the higher animals, and which is, as we shall find further on, a 

 decidedly epithelial production, presents a glistening white appearance like 

 porcelain, "but may also be met with of a more or less yellow or bluish 

 tint. Its surface appears at first quite smooth, but by the help of a lens 

 \ve may usually discover a number of delicate grooves encircling the 

 crown, of which Retzius counted 24 to the 1 mm., and which become 

 more frequent down below near the edge of the. cement. Like the 

 osseous coating of the dentine, the enamel is thinnest at the neck of the 

 tooth, where it is sharply defined against the cement. 

 From this point upwards it becomes stronger, at- 

 taining its greatest thickness in the middle of the 

 crown (comp. fig. 250, p. 261). Examined with 

 polarised light, enamel displays much more double re- 

 fracting power than either dentine or cement (Hoppe, 

 Valentin). 



From the examination of finely ground sections, or 

 of small portions of enamel macerated in acid, we 

 gather, that the tissue (fig. 261) consists of long 

 polyhedral fibres or pillars, closely crowded together, 



r , J , , , ., , . i? Fig. 261. Vertical sco- 



and held thus by a scanty amount ol some cement- tson of enamel, with sub- 



ing substance. K&XSL'SSi: 



These are called "enamel columns or prisms. o, enamel cuticle; &, 



They generally extend through the whole thickness Sees bet'we'en'these 



of the enamel layer, resting with one end on the den- latter; d, dentine with 



T -i ! , i ' i t- . T. _j? c its tubes. 



tine, while the other assists in forming the surface ol 

 the former. It is possible, however, that shorter prisms also occur, 

 which terminate at a greater or less distance from the dental tissue. 

 Their transverse diameter lies between 0*0034 and 0*0045 mm., and 



