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i8 art) until it nearly covers the anterior part of the inci fores, canini and fmall molares ofthe maxillary fuperior. The collection of this fubftance upon the large molares is partial in proportion to what is frequently found upon the teeth before mentioned. However, cafes have occurred, where I have fouud the bodies of all the teeth entirely covered with it, (except on the cut ting or grinding furfaces) which gave them a colour as black as foot. This fpecies of the tartar feldom affects the gums ;.but it is more rapidly deftruclive to the enamel of the teeth than the former. The cor- rofive qualities of this pernicious fubftance, cannot (it is prefumed) be more fully and fatisfaclorily explained, than by the following extract of a letter written by the celebrated Dr. Samuel L. Mitchel, Profeffor of Che- miftry, Natural Hiftory and Agriculture, in the Col lege of Columbia, to the Author, on that fubject : — " From a variety of confiderations, I have been led to believe, that acids are the great enemies of the human teeth ; and that of thefe, the feptic acid, or that acid which peculiarly characterizes the decay of the or ganic forms of plants and animals, or their parts, is the mod common and mod pernicious. It feems to be manufactured about the teeth and gums of fuch per- fons as fuffer the remains of food to collect and cor rupt thereabout, and to conditute the green tartar you mention, deftroying the calcarious enamel at a rapid rate. Without due attention to their mouths by people themfelves, or aid feafonably fought from a fkilful Dentift, (you know) the teeth and gums of human creatures become as nafty and abominable receptacles, as almoft any thing vile you can name. The remains of bread and meat putrefy there, after the fame manner that they would in any other place where there was free accefs of air, heat and moiflure. This putrefactive procef's among the inanimate remains of what has been chewed, and is left to the adhering teeth, produces the fame acids that reiult from putrefac-