Iviii INTRODUCTION. 



source of this fluid blastema (ib. g) appears to be the free inner vas- 

 cular surface of the capsule. As it approaches the dentinal pulp the 

 blastema acquires more consistence by an increased number of its 

 granules, and it contains more numerous and larger cells ; many of 

 these show a nuclear spot (ib. h') : others a nucleus and nucleolus : 

 the spherical nucleolar cells in the part of the blastema further 

 from the capsule are so numerous as to form an aggregate mass, 

 with a small quantity of the condensed blastema in the minute 

 interspaces left between the cells, which are pressed together into 

 hexagonal or polygonal forms, (ib. fig. 2, i). In this state they 

 constitute a great part of the enamel pulp, which is of consider- 

 able extent in the complex molar teeth of the Ruminants. The 

 appearance produced by these aggregated cells, in a section of the 

 tooth matrix of a Calfs molar, (PI. 122 a, fig. 9, e) is compared 

 by Raschkow to the actinenchyma of certain vegetable tissues, 

 and the connecting condensed blastema to threads of cellular 

 tissue. The field of the final metamorphosis of the cells into the 

 moulds for the reception of the solidifying salts is confined to 

 close contiguity with the surface of the dentinal pulp (ib. e', e'). 



Here the cells increase in length, lose all trace of their nucleus, 

 and become converted into long and slender cylinders usually 

 pointed at both ends, and pressed by mutual contact into a pris- 

 matic form (PL I. fig. 4, k, I). These cylinders have the property of 

 imbibing the calcareous salts of the enamel from the plasmatic fluid, 

 and of compacting them in a clear and almost crystalline state in their 

 interior : the disappearance of the nucleus being evidently the 

 condition of the absence of any permanent cavity, cell, canal, or 

 other modification of the mineral matter, at least in the enamel 

 fibres of the Calf. In the Human subject it is probable that the 

 cavity of the cylinder may be subdivided by a multiplication of 



