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70 battery. Let us follow the wire leading the current from the positive pole of the battery to the primary coil. Then the current passes through the coil and out by this wire to a little cup containing mercury. When the needle on the under surface of the end of the spring dips into the mercury, the current will pass through the mercury, along the spring, and then, by this other wire, back to the battery, entering it at the negative pole. I have also interpolated an electro-magnetic signal in the circuit, so that each vibration of the spring is also registered on the plate of the railway myograph.

Let us begin by sending a very few shocks per second to the nerve. This we can do by using the spring at its full length, thus causing it to vibrate slowly. You see the muscle twitching each time the spring dips into the mercury and comes out again, and we get a curve in which the separate contractions can be seen (see Fig. 33, b, c, d, e). But already, you will observe, the contractions are, as it were, piled upon each other, f. Thus the muscle contracts with the first shock; then it begins to relax; but before it has had time to relax it again