TRANSACTIONS OP THE SECTIONS. 15 



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-defined scolloped border, from which occasionally 

 processes are observed to arise at regular intervals. With respect to [the 

 actual process of]f the formation of the ivory, Mr. Nasmyth [candidly 

 avowed] f stated* that he was not prepared with a [perfectly] f satisfactory 

 theory, [but could] f 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 cor- 

 responding 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 latter when in a 

 state of transition. Mr. Nasmyth is of opinion, that from the spirally fibrous 

 frame work of the reticulations are evolved the spiral fibres of the tooth. 

 The diameters of the two sets of fibi-es exactly agree. The projections on the 

 formative surface of the pulp correspond to the centres of the cells, may be 

 traced to belong to their structure, and are evidently fibres passing upwards 

 from the pulp. Mr. Nasmyth has also ascertained that the fibres of perfect 

 ivory resolve themselves by decomposition into similar granules. He has not 

 discovered the manner in which the osseous matter is deposited in the cells 

 of the interfibrous substance, but he has observed that these cells are subdi- 

 vided into minute cellules, for they present the appearance of being filled with 

 smaller cells in certain progressive stages of development. But in whatever 

 aspect, said he, we view the formative organs of the tooth and the dental tis- 

 sues themselves, and whether we examine the latter during the process of 

 their developement or after their formation has been completed, we are every- 

 where met by appearances which denote a cellular or reticular arrangement. 

 Mr. Nasmyth concluded his paper by a notice of Schwann's [recent] f work 

 on the cellular character of primary tissues, dwelling [more particularly] f 

 on his views of the cellular organization of the pulp, from which [as he 

 showed] f his own were essentially different. 



Mr. Nasmyth read a paper " On the Structure of the Epithelium," which 

 he described as being composed of cells. He first alluded to the views of 

 Leeuwenhoek on the subject, contained in letters to the Royal Society, written 

 in 1674 and in 1684-5, and according to which this tissue is composed of 

 scales. The researches of subsequent inquirers tend to prove that scales or 

 cells of various forms exist on the surface of all mucous and serous membranes, 

 on the inner membrane of the vascular system, &c. Mr. Nasmyth described 

 the epithelium as a layer of substance destitute of vessels, covering the vas- 

 cular surface of mucous membranes. The scales, as they were first termed 

 by Leeuwenhoek, of which it is composed, are flat bodies, with a thick portion 

 or nucleus in their centre, and with very thin and transparent margins, which 

 are sometimes curved : their surface often presents numerous transparent 

 points, with very fine lines. The nucleus of the scale generally contains a 

 small body, which has been called the nucleus-corpuscle. If the secretion be 

 removed from an irritated mucous membrane, these bodies are found to as- 

 sume the appearance of cells ; but generally at the surface they resemble 

 scales, from having increased in size and undergone compression. In the 

 foetus the well-defined scales of the epidermis are not unfrequently seen ex- 

 ternally ; the rete Malpighii consists of newly-formed cells, and between the 

 two may be observed other cells in a state of progressive development. In the 



* The words in italics are in the Athenasum, but are not in the original manuscript, 

 f The words in brackets are in the original manuscript, but are not in the Athenaeum. 



