1. As the teeth are the only bones in the human frame which are exposed to the immediate action of foreign bodies,, they merit distinct and special consideration in this treatise on the General Physiology of man. The most remarkable fact in their history is, that unlike the other bones, the teeth which make their appearance in infancy, are removed at the age of seven or thereabouts, and another set come forward to supply their places.

2. The first set called temporary teeth, are just twenty in number, ten in each jaw. The two front teeth above and below, are known as central incisors, because they serve to cut the food. The teeth adjoining these are denominated lateral incisors, next to which come the canine or dog teeth, of which those in the upper jaw are called eye teeth. Back of these at either extremity of each dental arch are two larger teeth known as grinders from the fact that they operate like mill stones, in reducing the food to very minute particles in preparation for quick and easy digestion.

3. The second or permanent set has twelve additional teeth, six above and six below, making thirty two in all. The two next back of each eye tooth, are styled bicuspids, because they terminate in two points ; and the four extreme grinders are sometimes called wisdom teeth, because they do not generally appear until the individual arrives at mature age. Thus, there are twelve grinders or molar teeth in the second set instead of eight as in the first set; and there are eight bicuspids which are not found among the temporary teeth at all.

4. Each tooth consists of two distinct parts, called the crown and root; the former being that portion which projects from the gum into the cavity of the mouth, and the latter that which is buried in the socket. The incisors, eye teeth and bicuspids have one root each, the upper grinders three and the lower grinders two. The roots of the wisdom teeth are commonly compressed into one mass having little or no divergency, and in rare instances the bicuspids have two distinct fangs, while the upper molars have been known to have four or five distinct roots.

5. Every human tooth is composed of two distinctly organised substances, namely the enamel covering the crown, and the osseous or bony portion which constitutes the re remainder of the tooth. The osseous part is scarcely distinguishable from other bony structures excepting from its greater density. The enamel on the contrary, is remarkable for its extreme hardness resulting from its chrystaline structure. It consists of needle formed crystals, one extremity of which rests upon the bone beneath, while the other is presented to the food.

6. The teeth are found by chemical analysis to consist of nearly the same elementary substances as the other bones ; namely, phosphorus, lime, magnesia, soda, carbon, oxygen, chlorine, gelatine and water. As the teeth are a part of the living system, they are supplied with nerves, blood vessels and absorbents, not only by a central cavity extending from the point of each root to the middle of the crown, but by a membranous sheath enveloping the root called the periosteum, as is true of the other bones.

7. The teeth are firmly attached to the jaw or maxillary bone, by means of sockets called alveoli. In case of extraction the alveoli yield to moderate pressure and suffer the teeth to escape without any injury to the adjacent parts ; and as soon as the teeth are removed the investigating bone is sufficient to produce immediate absorbtion.

8. The first set of teeth begin to make their appearance through the gums, between the sixth and eighth month, and before the infant arrives at the thirtieth month all the teeth have assumed their natural position. The second dentition commences about the seventh year, and is commonly perfected before the fourteenth.

9. When the teeth are so much crowded as to disturb their regular arrangement; or when they press so hard upon each other as to destroy the enamel, one or more should be removed without delay. If this precaution should be neglected, an unsightly mal arrangement, or inevitable destruction of several of the teeth, will be the melancholy result. The removal of a sound tooth causes very little pain compared with the agony attending those which are suffered to become diseased.

10. It is impossible, under ordinary circumstances, to preserve the teeth for many years without keeping them very clean. Food lodges between them at every meal, and undergoes decomposition if not removed. A substance, called tartar, or salivary calculus, which is deposited from the saliva, adheres to the teeth, becomes very hard, and finally assumes a dark colour, if not constantly washed away with a brush and water. If food be suffered to putrefy in spaces between the teeth the process of mortification is extended to the teeth themselves; and if tartar collect in solid masses, the teeth become loose in their sockets and are thus utterly lost.

11. In order to keep the teeth and gums perfectly clean and healthy, it is necessary to wash them with a stiff brush and water several times in a day. No person of ordinary neatness would consent to eat with knives, forks and spoons, unless they were cleansed after every meal. The teeth are more liable to accumulate filth than any of these domestic utensils, and therefore need at least equally frequent washing. In the morning, after each meal, and before retiring to rest, are not too many times to purify the teeth with a brush and water, and once in each week with good tooth powder.

12. The Dentifrice or Tooth Powder, which I would re eommend in preference to all others which I have ever seen, is composed of the following ingredients, well pulverised in a mortar, and intimately mixed together:

Loaf sugar, half an ounce,

Cinnamon, half an ounce,

Gum Kino, quarter of an ounce,

Peruvian bark, three ounces,

Prepared chalk, six ounces,

Armenian Bole, five and a half ounces; making one pound avoirdupoise.

13. In addition to the above described dentifrice, every person should be provided with a good tooth brush, which should be laid aside as useless whenever it loses its stiffness and elasticity. A piece of gloss silk, well waxed, should be employed to cleanse the open spaces between the teeth, inasmuch as these are not easily cleansed with the brush alone. If tooth picks are used at all, they should be made of wood or quill, since those formed of any of the metals, particularly of steel or iron, are quite too hard, and therefore destructive to the teeth and gums.

14. If brushing the teeth and using the other methods of keeping them in order as above described, should fail of effecting the desired purpose, the assistance of the dentist should be put in requisition. With his scaling instruments, he can effectually remove every vestige of tartar, together with any other impurities lodged upon the teeth. Above all, abstain from the use of all kinds of powders and washes which render the teeth white by chemical action. These contain acid in one form or another, and are therefore de structive to the teeth.

15. Persons desirous of preserving their teeth in a sound and healthy state for many years, should consult their general health in all their habits of life, especially in relation to food and drinks. Neither solid nor fluid aliment should be taken into the mouth at either very high or very low tem perature, because sudden transitions from heat to cold, or from cold to heat, are liable to crack the enamel of the teeth by unequal expansion and contraction, as is readily ascertained by the assistance of the microscope. Teeth thus injured, almost always decay in consequence of the exposure of the bony substance of the tooth to the action of corrosive fluids.

16. There are three prevalent general causes of the destruction of human teeth, besides occasional accident: viz. accumulation of tartar, ulceration of the fangs, and dental gangrene. Ulcers of the fangs extend to the alveoli or sockets, which are also destroyed, together with the investing gum. The well informed dentist can best prescribe and apply the proper remedies for all these forms of dental disease.