General Anatomy, Applied to Physiology and Medicine, Vol. 2 (of 3)

by Xavier Bichat

Without refuting any one in particular, I would remark that they have one fundamental error, viz. that of considering osseous nutrition in an insulated manner, of not presenting it as a division of general nutrition, of admitting for its explanation reasonings only applicable to the bones, and which are not derived as consequences from those which serve to establish the nutrition of all the organs. Let us never lose sight of this essential principle, upon which rest all the phenomena of the economy, viz. that over a multitude of effects, a very small number of causes only presides. Let us mistrust every explanation which is partial and mutilated, which circumscribes the resources of nature according to the limits of our weak understandings.

IV. Peculiar Phenomena of the Development of the Teeth.

The teeth, differing in part by their texture, from the other bones, have also a peculiar mode of nutrition which we shall now examine. But as the knowledge of this supposes that of the general structure of the teeth, it is proper to explain here that structure, referring their description to the examination of the bones of the face.

Organization of the Teeth.

The teeth are formed by two substances, one external, of a peculiar nature, called enamel, the other internal, which is the common base of it, and the texture of which is the same as that of the other bones. They have besides a cavity which contains a spongy substance, as yet but little known.

Hard Portion of the Teeth.

The enamel of the tooth is only seen around the crown; some anatomists have thought that it extended a little upon the root, an opinion founded no doubt upon the extreme whiteness that the root often has in detached teeth, and which makes it impossible to distinguish the line of demarcation. But a very simple experiment proves this demarcation; it consists in macerating the tooth in diluted nitric acid. The acid immediately attacks both the root and the crown which it softens; but the first becomes yellow like almost all animal substances exposed to its action, whilst the other preserves its colour, and even becomes whiter. This experiment also proves that their respective natures are essentially different.

The enamel, thick on the top of the crown, grows thinner towards the root, an arrangement required by its use, which is to defend the tooth, to support principally the efforts of mastication, which are made especially upon the top of the crown.

This substance hard, compact, particularly when it has remained a long time in the air, acted upon with difficulty by the file, is composed of very close fibres, the direction of which cannot be traced. The medullary oil does not appear to penetrate it; it does not burn, but breaks by the action of fire, and is thus separated from the other substance, which, exposed to heat, at first becomes black, then burns like the other bones and gives out the same odour.

Is the enamel organized, or is it only a fluid which, oozing at first from the external surface of the tooth, afterwards becomes there hardened and concrete? This question is not I think easy to be resolved. The enamel has in fact attributes which seem equally favourable to both these opinions. On the one hand it is sensible, like every thing that is organized; it gives us, much more evidently than the hair or the nails, the sensation of bodies which strike it. The diluted acids, the vegetable especially, raise its sensibility so much, that the least touch becomes very painful a long time after their use. The teeth are then, as we call it, on edge. On the other hand the enamel has many characters that seem to denote a want of organization. 1st. It never inflames, or becomes the seat of any tumour, or any alteration which softens its texture; it never experiences any alteration, which by raising its life, renders it more sensible than in a natural state, as happens to the hair, for example, which ordinarily insensible, has a very great vital activity in the plica polonica. In fact we often judge of the vitality of organs more by their morbid alterations, than by their natural state. 2d. It appears that there does not take place in the enamel alternate exhalation and absorption of nutritive matters, or at least if it does, it is not sensible. Rubbing wears away this substance, which is never replaced; this is remarkable in old people, and in those who are in the habit of often striking their teeth together. We know that we file the enamel like an inorganic body, and that it is not reproduced, whilst the hair and the nails evidently grow after being cut. File the extremity of a long bone after amputation; fleshy granulations will soon grow upon the filed surface; the action of the instrument will be a stimulus which will develop the vital phenomena.