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156 at the foot. Fatigue, so far as amplitude of contraction is concerned, has scarcely begun. By and by, however, as the muscle becomes fatigued, the amount of contraction diminishes, until the muscle does not contract at all, but the duration of the contraction increases throughout the whole contraction. The muscle is gradually losing time in doing its work. When does it lose time? In contracting or in relaxing? You observe the slope of the successive curves; the way in which they open out, as seen if you study each from the bottom to the top of the diagram, shows that it loses time during relaxation. During fatigue a muscle after contracting returns more slowly to its original length.

These results are consistent with our experience. After a thirty mile walk, we feel unwilling to take each step; it is only by a strong effort of the will that we force the muscles to contract. Like jaded horses, they require the whip and spur. The muscular contractions required for each step, however,