Dr. S. Baker, of Portsmouth, N. H., has sent us three human teeth, one of which is perfect, another has been steeped in a solution of cream of tartar and it is slightly corroded, while the third, that has been immersed in saleratus, is completely caten into holes. We do not, however, think this is a fair test, as we perfectly well know that in baking, it would be decomposed, and the alkali which it contains would form some less virulent compound with one of the constituents of the bread, most likely an acetate of potash, in which case the teeth wonld not be much injured. Carbonate of potash or saleratus cannot be in itself so very iniurlOus; for in Britain, where teeth are proverbially good, there is a great . quantity of baking powder used, one of whose j chief constituents is this same salt. k The dentists are evidently on the wrong S track in trying to discover the cause of decay in American teeth, and we have an idea that were they to turn their attention to the climate and general habits of life among m, they would be nearer the mark. Let them try.