3d. Contractions are excited when one of the armatures and the arc consist of mercury, by making the mercury to run down on the muscles placed below it. There is no reason here to suspect that the stimulus produced by the impulse of the mercury has any share in the phænomenon, as it is sufficiently proved by experiments that this is not the case. 4th. That when there is no reason to suppose a want of equilibrium in the electricity of the armatures and of the arc, animal electricity is excited, and produces contractions. 5th. That when the armatures and arc are formed of charcoal, the same results will be obtained; which evidently proves that the animal electricity is not produced by the metals. [3] The title of the work from which this and the following dissertation are translated is, _Joannis Aldini de Animali Electricitate Dissertationes duæ_. Bononiæ 1794. [4] There seems here to be some mistake, as the author says, towards the end of this Dissertation, that he produced contractions in a frog by employing coals, both as an arc and as armature. T. [5] The celebrated Volta, in a letter which I received from him, announcing that he had observed the same phænomena as those described in my Dissertation, published the preceding year, § xxii. p. 19. added the following remarks: “The best and easiest method of performing this experiment, is to immerse in a large earthen or glass vessel, filled with water, a silver dish, in such a manner that a part of it remains above the surface of the water; to apply to the tip of the tongue a small bit of tin foil, so that part of it shall hang out of the mouth; to bring this tin foil into contact with the silver vessel, either immediately or by means of a third piece of metal; lastly, to immerse the hand in the same water gradually, if you are desirous of perceiving gradually on the tongue the acid taste; or suddenly, and at once, if you are desirous of perceiving it at once and in the highest degree. A silver spoon half immersed in the water, or instead of the dish, if not too small, will produce nearly the same effect as I have already mentioned. The case is not the same with a slender silver rod or wire, which if gradually immersed will scarcely produce any taste at all. If the vessel which contains the water be itself of silver, a dish or spoon will then be unnecessary. This vessel forms the best armature for the water; and to perceive the taste very strongly, it will be sufficient to immerse the hand in the water, or to bring the tin foil which hangs from the mouth into contact with the vessel.