Substance of a lecture on the functions of the mouth, and the structure of recent and fossil teeth / [Alexander Nasmyth].

  • Alexander Nasmyth
Date:
[1840]
Catalogue details

Licence: Public Domain Mark

Credit: Substance of a lecture on the functions of the mouth, and the structure of recent and fossil teeth / [Alexander Nasmyth]. Source: Wellcome Collection.

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    that, according to liis researches, the fibres of the ivory were baccated, and presented the appearance ofrows of beads, as he shewed in various drawings. The in- terfibrous substance he had also disco¬ vered to be decidedly cellular. When the growth of the ivory is completed, the primary function of the pulp ceases; but its residue Mr. Nasmyth has often ob¬ served to ossify under the influence of dis¬ ease in the higher animals, and normally in the lower. Interesting examples of the normal occurrence of this irregular osseous formation are presented by the teeth of the sloth family ; and those of the fossil megatherium are very interesting examples of it. It occurs generally in the teeth of all fishes, in the walrus, and many others. Mr. Nasmyth has thought it worthy of being ranked as a distinct fourth tooth-bone substance. The enamel which surrounds the ivory he has discovered to be distinctly cellular, and characteristically so in different animals. He has also traced on the surface of this substance a capsule, which had escaped the notice of preceding writers. A coating has long been observed, and acknowledged as most obvious, on the grinder of the elephant, where it fills up the spaces, which would otherwise be un¬ occupied, between the layers of enamel, cementing the whole of this convoluted compound-tooth into one solid mass. It is to be observed in all teeth of this kind, which are required to perform the office of a grinding-stone in pulverizing the food; and this substance is provided in order to fill up the interstices, and that there may be produced a succession of surfaces efficient for that purpose. The surface presents three substances in succession, differing in texture, hardness, shape, and disposition. The enamel is, of course, the hardest, and presents a beautiful undulating edge. The process of trituration wears down the ivory on the one hand, and the cement on the other, these being of softer texture than the enamel, and thus an irregularity of surface is necessarily produced. The cement being again a little softer than the ivory, a most efficient grinding surface is kept in constant order by the very act and habitual exercise of the function of mastication. This beau¬ tiful adaptation of means to an end, is only a single instance of the design which is demonstrated in every part of the machi¬ nery of the mouth. Mr. Nasmyth stated, that, in pursuing this inquiry, he had found, that this capsule of crusta petrosa is pre¬ sent in an attenuated state, and can be de¬ monstrated in a great number of teeth, which have been hitherto considered de¬ void of any covering at all external to the enamel. The lecturer concluded his eloquent dis¬ course, by showing the importance of the study of the teeth in geology. From their being so characteristically organised in. different animals, he said, they became much more valuable guides than fossil bone. Certain fragments of fossil remains can be demonstrated to perfect conviction to be fragments of teeth; and, from exa¬ mining these by the microscope, they can be proved (so typical is their structure) to have belonged to animals of a certain order and conformation. Put in possession of this scrap of information, we can further proceed to delineate the animal in each particular case in all its details, with a de¬ gree of certainty nearly mathematical. From this knowledge follows necessarily an idea of the country or locality in which alone the animal, thus restored, could exist; and hence, from an examination of minute, insignificant, and, to common observers, utterly worthless fragments of tooth-bone— from slight particles of crumbling matter— we derive the means of contemplating whole regions of the face of the ancient globe, covered by its animal tenants. Mr. Nasmyth finally said, that he had been led to the study of the structure of the teeth, from his having considered it his duty to investigate the novel doctrines which had been lately propounded, in the hope of their throwing new light on mala¬ dies daily passing under his notice. And this duty, like all others which are exe¬ cuted with willingness and alacrity, had been to him a source of unmingled gratifi¬ cation ; for, in performing it, he had not only been rewarded by arriving at a com¬ prehension of many phenomena of disease which had been hitherto obscure, but had been so fortunate as to establish results which would, he hoped, constitute some advance in this department of anatomical science. Wilson & Ogilvy, 57, Skinner Street, Snowhill, London.
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