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76 to relax, at first slowly, then rapidly, and again more slowly, and the time, shorter than the time of contraction, is less than three-hundredths of a second. Lastly, as a rule, we find a few smaller waves, as if, in recovering itself, the muscle had been thrown into a kind of vibration. Sometimes the muscle, unless it be drawn out by a weight attached to it, does not return at once to its original length, but remains somewhat shortened. This occurs readily in muscles that are fatigued.

The question at once suggests itself as to whether the contractions of the muscles in our bodies are of the nature of twitches, that is, single contractions, or of tetanus. We can apparently flex and extend the arm with great rapidity, and one would naturally suppose that such contractions of the biceps muscle in front, and of the triceps muscle behind, were simple contractions. There are strong grounds for holding, however, that they are not so, but that the movement is really a short tetanic contraction. There can be no doubt that when we firmly contract a muscle and maintain the contraction, the muscle is in a state of tetanus, in which the quivers of the partial contractions