Ix INTRODUCTION. 



seat of the calcifying processes. (1) Here, as in the dentinal and 

 enamel pulps, the calcareous salts are selected and arranged by 

 the assimilative, selective, or intus-susceptive, properties of the cell- 

 walls and by the repulsive power of their nuclei. (2) 



The blastema or fundamental tissue of the capsule is, at first, 

 semitransparent and of a pearly or opaline colour ; but is soon richly 

 ornamented by theplexiform distribution of the blood-vessels, (PI. II). 

 As the period of its calcification approaches, which is later than 

 that of the dentinal pulp, it becomes denser, and exhibits nume- 

 rous nucleated cells. The blastema itself (PI. I. fig. 5, n) presents more 

 evidently a fine cellular or granular structure in which the calcareous 

 salts are impacted in a comparatively clear state constituting the frame- 

 work {n') of the ceraental tissue. The characteristic features of this 

 tissue are due to the action of the proper nucleated cells (ib. m) upon the 

 salts of the plasma diffused through the blastema in which those 

 cells are imbedded. The cells being characterised by a single large 

 granular nucleus (ib. p) which almost fills the clear area of the cell 

 itself. If, when the formation of the cement has begun in the incisor 

 or molar of a Colt, one of the detached specks of that substance, with 

 the surrounding and adhering part of the inner surface of the 

 capsule in which it is imbedded, be examined, these nucleated 

 cells are seen, closely aggregated around the calcified part, in con- 

 centric rows ; the cells of which are further apart as the rows 

 recede from the field of calcification. Those next the cement (ib. o) 

 rest in cup-shaped cavities in the periphery of the calcified part just 

 as the first calcified cells of the thick cement which covers the 



(1) This has led me to doubt whether the altered blood-discs of the capillaries of the 

 dentinal pulp are converted into the cells of the pulp which occupy the place of the capillaries in 

 the calcifying field. 



(2) It might be supposed that the cell-membrane and the surface of the nucleus were in 

 diflferent electrical states. 



