M. Volta’s discovery of the sensation produced upon the end of the tongue, by coating its upper and under surfaces with different metals, led me to compare this sensation with that produced by electricity. I found a very considerable difference between them. Both, indeed, are subacid, but as unlike to each other, as the taste of vinegar is to that of diluted vitriolic acid. That occasioned by the metals is accompanied with what is familiarly called the metallic taste; and differs according to the metals employed. With the greater number of metals it is scarcely perceptible. With zinc and gold, I think, it is strongest; next so with zinc and silver, or molybdena, and insufferably disagreeable with any of them. The sensation is most distinct when the tongue is of its ordinary temperature, and when the metals are of the same temperature with the tongue. When either the tongue, or the metals, or both, are heated or cooled, as far as can be borne without inconvenience, scarcely any sensation is produced. That this difference in the effect is owing to the alteration which has been produced in the state of the tongue, and not to that in the temperature of the metals, is evident from experiments which I have already related; from which it appears that neither the conducting, nor the exciting powers of metals are affected by differences of their temperature. But I have found it the uniform result of many experiments, that both the life and irritability of the most vigorous frogs is completely destroyed in a few minutes, by placing them in water heated to 106 degrees of Fahrenheit’s scale. Cold, however, though it appears to affect the sensibility of the tongue nearly as much as heat, did not, in one or two instances in which I tried it, affect the irritability of the muscles of a frog. Some separated legs contracted equally well after they had lain upon a piece of ice for some hours, as they did before they had been in that situation. Whatever has a tendency to blunt the sensibility of the tongue, as laudanum, a strong solution of opium in water, distilled spirits, acids, &c. diminishes the effect of the metals. Acids, I think, diminish it least.