Proceedings of the British Association. 1 29 



structure of the teeth, Mr. Nasmyth treated principally of the interfi- 

 brous substance, which he said was not "structureless," as has been er- 

 roneously stated, but decidedly cellular. The fibres themselves he 

 described as presenting an interrupted or baccated appearance, as if 

 made up of compartments, which differ in size and relative position in 

 various series of animals. He detailed their peculiarities in the human 

 subject, in some species of the monkey tribe, and in the oran-outan. 

 After the earthy matter of teeth has been removed by acid, the animal 

 residue, he stated, consists of solid fibres, and if the decomposition be 

 allowed to continue, these fibres present a peculiar baccated appearance. 

 The general appearance of the fibres treated by acid is similar to that 

 of the fibres of cellular tissue generally, and the diameter of each cor- 

 responds exactly to the calibre of the dental tube, as described by Ret- 

 zius, and which, according to that writer is pervious, although, at the 

 same time, he says, that it is always more or less filled with contents 

 of an earthy nature. With regard to the internal structure of the pulp, 

 Mr. Nasmyth stated that the number of minute cells presenting them- 

 selves in its interior, in a vosicular form, is very remarkable. They vary 

 in size from the ten-thousandth to one-eighth of an inch in diameter, and 

 are evidently disposed in layers. The parenchyma of macerated pulp 

 is found to be traversed by vessels, and to be interspersed with granu- 

 les. The arrangement of these cells or vessels, Mr. Nasmyth thinks, 

 may account for the shrinking or nearly total disappearance of the pulp 

 which he has frequently observed : their use in the economy of the part 

 he has not yet ascertained. They are evidently filled either with air or 

 fluid. He finds that they exist on the formative surface of the pulp. 

 Mr. Nasmyth next proceeded to the nature of the process by which the 

 ivory is developed. The formative surface of the pulp, which is in ap- 

 position to the ivory, and by which the latter is produced, he described 

 as presenting a general cellular arrangement, which he denominated re- 

 ticular, resembling a series of skeletons of a desiccated leaf. This reti- 

 cularity is found to have peculiar diversities in different classes of ani- 

 mals. Mr. Nasmyth has found that a similar appearance is presented 

 by the capsule and by the capsular investment of the enamel. The 

 leaves or compartments of the reticulation are surrounded by a well-de- 

 fined scolloped border, from which occasionally processes are observed to 

 arise at regular intervals. With respect to the formation of the ivory, 

 Mr. Nasmyth stated that he was not prepared with a satisfactory theory, 

 and would only submit a few observations based on his own researches. 

 On the surface of the pulp, he said, are found innumerable detached 

 cells with central points, which latter are at regular intervals corres- 

 ponding in extent to those existing between the fibres of the tooth. 

 The cellules of the fragments of the ivory which are found scattered on 

 the pulp, resemble exactly in size and appearance the cellules of the lat- 

 ter when in a state of transition. Mr. Nasmyth is of opinion that from 

 the spirally fibrous frame-work of the reticulations are evolved the spi- 



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