Page:Life in Motion.djvu/53

 LECTURE II Myograph— Electricity as stimulus— Action of nerve— Continuous current— Interrupted current— Induction coil— Graphic method— Time in physiological phenomena— Chronographs— Study of contraction— Latent period.

last lecture we saw that when the nerve connected with a muscle is irritated, the muscle changes its form, that is to say, it becomes shorter and thicker. It is this shortening or, as it is termed, contraction, that causes the movement of one part of the skeleton upon another. Let us repeat the experiment and study it more closely. This time we shall make use of an apparatus called a myograph or muscle-writer, and by means of it the muscle will write down its movement on a smoked-glass plate. The instrument is shown in this diagram. The upper end of the femur is fixed by the clamp C, sliding on the pillar B, and the tendo Achilles is attached by a hook to the horizontal bar EE, which carries a 3