TRANSACTIONS OF THE SECTIONS. 19 



posing the pulp. The contents of the cells are evidently air or fluid ; but 

 they are so extremely minute, that he had not yet been able to ascertain 

 which. But the main feature of his position, viz. that the pulp consists 

 throughout of vesicles or cellules, and that these exist equally in the com- 

 partments of its reticulated surface (which he should immediately proceed 

 to describe), his researches, he apprehended, had placed beyond the reach 

 of doubt. 



5. With respect to that difficult subject, hitherto so unsatisfactorily eluci- 

 dated by anatomists, the production of the ivory itself, Mr. Nasmyth con- 

 fessed that he had long devoted himself to its examination without much 

 success, and that even now he was far from regarding his researches as 

 complete or decisive. The formative surface of the pulp had first engaged 

 his attention ; this he had found to present a regular cellular arrangement, 

 which he had denominated reticular, and which may be described, he said, 

 as resembling the skeletons of desiccated leaves. (Of this structure, both 

 in its general appearance, its individual parts, and its particular varieties, 

 Mr. Nasmyth exhibited numerous drawings and diagrams to the Members 

 of the Association.) The general compartments of the reticulation are oval, 

 and overlap each other; when insulated, their structure is seen to be curious 

 and regular. He had first found them on the pulp of the human tooth, and 

 afterwards on that of all other animals which he had had an opportunity of 

 examining. The leaves of the reticulation are surrounded by a well-defined 

 scolloped border, on which processes are occasionally observed at regular 

 intervals. He had extended his observations to the capsule, and had found, 

 on its formative surface, a similar reticular arrangement. Mr. Nasmyth now 

 approached the question as to how the vesicular or cellular pulp, with its re- 

 ticular and imbricated surface, was concerned in the production of the ivory. 

 He was aware of the impossibility at present of completely describing this 

 process, which anatomists hitherto had for the most part eluded or passed 

 cursorily over, and should confine himself to a few facts which he had esta- 

 blished, and which he hoped would throw some light on the subject. In the 

 young tooth, he said, at the period of the formation of the first layer of 

 ivoiy, there are found on the surface of the pulp innumerable detached cells 

 with central points. These cells frequently form a regular and complete 

 coating, studded with points which are placed at intervals, corresponding in 

 extent, as it appeared to him, to those between the fibres of the adult tooth. 

 He exhibited diagrams of layers of these cells in different stages of their 

 transition into ivory. The points are rendered visible from the greater 

 opacity of the intermediate material, and will be seen to absorb or reflect 

 the light according to the difference in the focal distance. A comparison of 

 the superincumbent perfect ivory, with the surface of the pulp beneath, is 

 always easy (at any rate at an early stage), because portions of the former 

 remain adherent to the latter, and fragments of the dental bone are found 

 strewn over it, especially in human teeth. The cellular conformation of 

 these fragments is always evident, and in size and appearance they are per- 

 fectly in accordance with the cells of the pulp. He concluded therefore, that 

 the ivory is neither more nor less than the ossified pulp, and that it can in no 

 wise be regarded as an unorganized body. That the ossification is effected 

 by means of a peculiar arrangement of minute cellules, seems to be evident 

 from the constant presence of granules in the body of the pulp, and on its 

 surface ; and from the subdivided appearance of the cells, when in a state of 

 transition into perfect ivory. As almost all preceding writers had, he be- 

 lieved, uniformly described the ivory as a secretion from the pulp, he wished 

 particularly to insist upon its being an organic deposition of ossific matter in 



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