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In man, the several classes of the teeth are so similarly developed, so per- fectly equalized, and so identically constructed, that they may be considered as the true type from which all the other forms are deviations.

For the accomplishment of their office, the teeth must be endowed with pro- digious strength : for the fulfilment of purposes immediately connected with the apparatus of digestion, it is necessary that they should be placed in the neighbourhood of exceedingly soft, delicate, irritable, and sentient organs. That they may possess the requisite degree of strength, they are constructed chiefly of bone—the hardest organized substance. Bone, though not as sensible as some other parts of the body, is nevertheless sentient. The employment of a sensitive body in the office of breaking down the hard substances used as food, would be to change the act of eating from a pleasurable into a painful opera. tion. It has been shown that provision is made for supplying to the animals never-failing source of enjoyment in the annexation of pleasurable sensations with the act of eating ; and that, taking the whole of life into account, the sum of enjoyment secured by this provision is incalculable. But all this enjoy- ment might have been lost—might even have been changed into positive plia- ntly, must have been changed into pain, but for adjustments numerous, minute, delicate, and, at first view, incompatible.

Had a highly-organized and sensitive body been made the instrumento cutting, tearing, and breaking down the food, every tooth, every time it comes in contact with the food, would produce the exquisite pain now occasionally ao perienced when a tooth is inflamed. Yet a body wholly inorganic, and there- fore insensible, could not perform the office of the instrument ; first, becauset dead body cannot be placed in contact with living parts without producing irri- tation, disease, and consequently pain ; and, secondly, because such a body, being incapable of any process of nutrition, must speedily be worn away by friction, and there could be no possibility of repairing or of replacing it. The instrument in question, then, must possess hardness, durability, and, to a cer- tain extent, insensibility ; yet it must be capable of forming an intimate union with sentient and vital organs, must be capable of becoming a constituent pot of the living system. To communicate to it the requisite degree of hardness, the hard substance forming its basis is rendered so much harder than common bone, that Bonn Or siologists have even doubted whether it be bone—whether it really possess.' true organic structure. That there is no ground for such doubt, the evidence is complete. For, I. The tooth, like bone in general, is composed partly of an earthy and partly of an animal substance; the earthy part being completely removable by mace- ration in an acid, said the animal portion by incineration, the tooth under each process retaining exactly its original form.

2. The root of the tooth is covered externally by periosteum ; its internal cavity is lined by a vascular and nervous membrane ; and both structures are intimately connected with. the substance of the tooth. If these membranes THE preceding volume of this admirable work was chiefly occu- pied with two subjects. The first embraced a general view of organic life, and the analogous processes by which it is supported, from the lowest plant up to the "paragon of animals," man him- self. The second contained an anatomical description of man's structure and organs. The present volume is confined to an ela- borate, but popular, condensed, and deeply interesting account of the functions some of these organs perform for the support of life. The processes of respiration, digestion, secretion, absorption, excretion, and the probable generation of animal heat, together with nutrition—the end for which the lungs, the stomach, the liver, the absorbents, and the other machines of the body are set in motion—are all minutely yet comprehensively described, and the secret operations of nature laid open. This is done, too, with a mastery equalling, if not surpassing, the introductory essay on Life in the first volume. The expositions have the clearness and conviction of a mathematical demonstration; the style derives from the fulness of its matter a weight and terseness that mere eloquence, in the common meaning of the word, could never attain to; and if the facts themselves cannot be new, they are collected with so much knowledge, arranged with so much ability, and are illustrated with such distinctness, that they form as it were an original whole, from which even the medical man will gain a more enlarged view of our animal economy than the schools or the dis- secting-room have given him. Whilst, as in the first volume, the general reader at every step will have his knowledge extended, his mind expanded, and his astonishment excited at his own construction. "We are fearfully and wonderfully made."

The only manner of conveying an idea of the book will be to make an extract; and we will take the subject of Teeth, as one of general interest. Let the reader consider that there are eight processes of digestion, of which the following quotation only re- lates to a part of one of them—mastication. Let him next con- sider that seven subjects as extensive as digestion are treated of. and then, by imagining a manner of treatment as various as the nature described, a general conception may be formed of the second volume of the Philosophy of Health. reallv disttibute their blood vessels and nerves to the substance of the tooth, (which there is no reason to doubt') the analogy is ideutical between the strue. paint a picture of the little children brought to (Arial, for a church at

tare oi the teeth and that of bone Liverpool attached to the Asylum for the Blind. 3. Thorigh the blood-vessels Of the teeth are so minute that they do not, oder ordinary circumstances, admit the red particles of the blood, and though no colouring matter hitherto employed in artificial injections has been able, on THE PICTURE-BOOKS OF THE SEASON.

aecouut of its grossness, to penetrate the dental vessels, yet disease sometimes THE " Annuals"—like other superfluities designed for ornament and accomplishes what art is incapable of effecting. In jaundice, the bony sub.

stance of the teeth is occasionally tinged with a bright yellow colour ; and in

persists m who have perished by a violent death, in who the circulation has been gradually exchanging intrinsic excellence fo outward show. At first suddenly atrested, st is of a deep red colour. Moreover, when the dentist files every Annual was a little casket of gems of art: each vied with the other, not only in outward elegance, but in the rarity and brilliancy of a tooth, no pain is produced until the file reaches the bony substance ; hut the

iustant it begins to act upon this part of the tooth, the sensation becomes suffi- its contents. The best pictures of the Spring exhibitions used to be

ciently acute. engraved in tbeChristmas Picture-books. But most of those containing These facts demonstrate that the bony matter of the tooth, though modified the choicest specimens of graphic skill have become extinct. The An. to fit the instrument fur its office, is still a true and proper organized sub- niversary did not realize its title ; Turner's Annual Tour was only re.. stance. peated once ; and now the Amulet charms no more ; and the Literary Each tooth is divided into body, neck, and root. The body is that part of Souvenir is no longer a token of remembrance. The Souvenir, in its the tooth which is above the gum, the root that part which is below the gum, enlarged size and under its second title of Cabinet of Modern Art, was abet the neck that pat t where the body arid the root unite. The body, the es.

sential part, is the tooth properly so called—the part which performs the whole ;Yolk for which the instrument is constructed, to the production and support of whielt all the other ittstruments are subservient.

of considerable heir character; but the others have rather deteriorated than improved. ble size, termed the dental cavity, which, large in the body This pulp, highly vascular and exquisitely sensible, is composed almost entirely

support of its vitality, and for its connexion with the living system, over all

that portion of it which is above the gum, and which constitutes the essential part of the instrument, there is poured a dense, hard, inorganic, insensible, all I) ut italestt uctible ubsta snce, termed enamel ; a substance Inorganic, composed nw 2. The roots of the tooth, when there are more than one, deviate from a straight line ; and this deviation from parallelism, on an obvious mechanical the medallists. prineiple, adds to the firnmess of the connexion.

far as the neck, where it terminates, and where the enamel begins : this mem- 5. Lastly, the vessels and nerves, which enter at the extremity of the root, some badge, is very elegant.

face and skull to the brain, would severely injure that tender organ, and effec- gation. is becoming a festive occasion.

4. By the gum. the painted flies they enclose. These membranous substances, even more than the cancellated structure of