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 frame, by which the instrument may be screwed to the table. On the top is a square block of vulcanite, a, bearing two rectangular bars of brass, b and c, which may be joined by the handle, d, carrying a horizontal piece of brass. Suppose wires from the battery are connected with c and b. The key is closed when the arm is horizontal, and the current runs along the horizontal piece of brass. On moving the handle, d, backwards and to the right, the brass arm is raised and the contact between b and c is broken. The key is then said to have been opened and the flow of the current is interrupted.

Well, you observe that when I close the key, and the current is sent through the nerve, the muscle gives a contraction, but it quickly relaxes, and no change, so far as the muscle is concerned, is visible while the current flows through the nerve. Now I open the key so as to stop the flow of the current through the nerve, and again there is a sudden twitch. If I open and shut the key quickly there is a twitch with each movement of opening and of shutting, and you see the muscle passing into the more permanent state of contraction