TRANSACTIONS OP THE SECTIONS. 21 



ter of the tooth, the appearance of fibres as described by these writers was, 

 Mr. Nasmyth allowed, distinctly evident. If, however, a different section be 

 made, for instance, one near the surface, parallel to the long axis or vertical 

 direction of the tooth, an appearance presents itself which had induced him 

 to take a difierent view of the structure of this substance. This was an ap- 

 pearance of compartments or divisions of a semicircular form ; the convexity 

 of the semicircle or arch generally looking upwards towards the free external 

 portion of the tooth. Several diagrams illustrating this conformation were 

 here exhibited. In sections, both of enamel and ivory, there will always be 

 observed, said Mr. Nasmyth, isolated cells near the margin, which admit of 

 their form and structure being carefully studied. 



All the analyses hitherto published of the chemical composition of the 

 enamel had favoured the conclusion, that it contains only a very small portion 

 of animal matter ; but when he had detected the cells or compartments just 

 mentioned, he could Tiot but infer that each of these had for its basis and 

 support a framework of animal tissue. He had accordingly immediately re- 

 quested his friend Dr. Thomson, of Glasgow, to favour him with a complete 

 analysis of the chemical composition of the different structures of the teeth in 

 their various states of health and disease. The results of this analysis, so far 

 as it had been proceeded with, were highly interesting. He laid them before 

 the Members of the Association in a tabular form, observing, that with respect 

 to the enamel. Dr. Thomson's experiments quite favoured the conclusion tJiat 

 it was provided xvith an animal basis, a result which, as he had just observed, 

 he had previously arrived at by means of microscopic researches. 



9. In a separate paper read before the Medical Section of the Association, 

 Mr. Nasmyth detailed his investigations into the structure of the Epithelium, 

 which he stated to be also composed of cells. Leeuwenhoek, he said, had 

 been the first to give an accurate account of the structure of this tissue*. 

 Leeuwenhoek stated the human epithelium and epidermis to be composed of 

 scales, of which he has left very accurate descriptions and delineations. He 

 alluded to the scales or cells on the mucous membrane of the mouth, which 

 have since been proved to exist in various forms, on the surface of all mucous 

 and serous membranes, on the inner membrane of the vascular system, &c. 

 The Epitlielium Mr, Nasmyth defined to be a layer of non-vascular but not 

 therefore inorganic substance covering the vascidar surface of mucous mem- 

 branes. If, said he, a mucous membrane, for instance the conjunctiva, or the 

 buccal, be slightly rubbed, the microscope will show that numerous small 

 particles have been detached from it. At first, being flat bodies with a cen- 

 tral nucleus (sometimes absent), and a very thin margin (sometimes curved), 

 they present the appearance of scales, as they were denominated by Leeuwen- 

 hoek. Their surface often presents numerous transparent points with veiy 

 fine lines. The nucleus generally contains a small body, the nucleus-corpuscle. 

 These so-called scales, when removed from an irritated mucous membrane, 

 are found to be smaller and more globular; they have then the usual nucleus 

 and nucleus-corpuscle, but the surrounding structure is smaller, and in the 

 form of a cell. Here and there, too, the nucleus and its corpuscle are seen 

 to be isolated. In a section of the epithelium and mucous membrane nume- 

 rous nuclei are found in apposition to the latter, which, more externally, are 

 surrounded by a cell, whilst at the surface, this cell, compressed, assumes the 

 appearance of a scale. In the layer of epithelium, from the under surface of 

 the tongue of the calf, these bodies in their various stages of granules, cells 

 and scales, may be well seen, according ds the object is removed from or ap- 



• See his Letters to the Royal Society, which may be found in the 3rd and 4th volumes of 

 his collected works. 



