320 On the Structure and Development of Dentine. [Mar. 5 



dentine are partly due to the difficulties met with in the investigatioi 

 of this tissue, soft and hard parts haying to be retained in theii 

 natural relations to each other. Decalrification of the dentine b 

 acids has been resorted to, a mode of preparing microscopical object) 

 for study which is open to many objections. Sections cut by 

 process recommended by Dr. L. A. Weil, of Munich, exhibit th 

 natural relations of pulp and tooth without the necessity of resortin] 

 to decalcification. Fresh specimens are fixed in sublimate, passe* 

 through gradually increasing strengths -of spirit to absolute alcohol 

 and slowly impregnated with a solution of desiccated balsam ii 

 chloroform, dried with more balsam over a water-bath, and cut dowi 

 on a stone with water. The present investigation was undertake] 

 with the aid of this process, controlled by the examination of othe 

 specimens cut by the more ordinary methods. 



Processes or bundles of fibres are seen, incorporated on the on 

 side with the dentine, and on the other with the connective tissu 

 stroma of the pulp; some of the bundles give evidence of partia 

 calcification, reminding one of similar appearances in the calcificatioi 

 of membrane bone. Cells are seen included in the bundles and lyin 

 parallel to their course ; these cells, it is concluded, form together wit 

 the odontoblasts the formative cells of the dentine, the calcification c 

 which tissue should be looked upon as in part, at least, a secretio 

 rather than a conversion process, the cells secreting a material whic 

 calcifies along the lines of and among the connective tissue fibrei 

 the cells themselves not being converted into dentine matrix. Theg 

 appearances are seen in the rapidly forming dentine of a growin 

 tooth, as well as in more fully developed specimens. An examinatio 

 of other Mammalian teeth reveals similar appearances. The dentin 

 of the incisor of the Rat (Mug decumanus) shows with great distincl 

 ness the incorporation of the connective tissue fibres with the dentine 

 and there is a marked striation of the dentine near the pulp cavity, 

 parallel with these fibres. The ivory of the Elephant's tusk shows 

 the same relation of connective tissue to formed dentine. VMO- 

 dentine exhibits a very well defined connective tissue layer sur- 

 rounding the pulp. This layer has hitherto been looked upon as 

 consisting of odontoblasts, but this tissue shows no nuclei, and has 

 the characters of a layer of flattened connective tissue fibres a layer 

 of nucleated cells in close apposition to the dentine, probably being 

 the real odontoblasts of vaso-dentine. 



