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6 crown ; this fubftance from its extreme hardnefs, is peculiarly calculated to preferve the internal parts, and to refill the imprefllon of hard fubftances, and are in a found ftate of health, while the gums covers the whole of that part of the teeth that appears out of them. — care Ihould be taken to preferve Very great this outer coat or enamel ; for when once deftroyed, the tooth is expofed to the impreffions of heat and cold, and will be acted upon by acidities, which are peculi arly iujurious, as they never fail to complete the work of deftruclion in a very lhort time. The fecond fub- fiance is near the texture and colour of all human bones,. it is formed immediately under the enamel in the body of the tooth, and includes the neck and root. The third confifls of the internal part commonly called the bulb, or pulp, which is much fofter than either of the other fubftances, and is extremely fufceptible, for when touched by an inftrument, or affected by acids communicates a thrilling painful fenfation to the nerve or chord of the tooth, which, if expofed by a caries of the enamel and bony part, foon produces excruciating pain. — The necks of the teeth are covered by the gums adhering or growing to them, which effeclually pre vents faline particles and other injurious fubftances from entering the alveoli or fockets. — The root is a continuation of the fame fubftance and colour as the neck, at the extremity of which, is formed a fmall hole, enlarging as it proceeds towards the crown or body of the tooth, and filled with an artery, a vein, and ner vous filament, which communicates to the bulb ; the root and focket is both covered with a periofteum or membrane that is vafcular, and is attached to the where it covers the alveoli. gum, The human teeth are diftinguifhed by the following names, viz. the incifores, canini, molares, and fapi- entaE. The incifores (derived from incifor, to cut) confift of the four front teeth in each maxillary or jaw, and have but one root. — The canini confift of four in