Page:Life in Motion.djvu/55

Rh horizontally moved, sliding in grooves. The nerve is stretched over wires coming from a battery or induction coil, so that it may be irritated by an electric current. When the nerve is irritated, you observe the muscle contracts, lifts up the lever E E, and the

marker J draws a vertical line on the plate G. We then push the plate a little farther on, and again stimulate the nerve by a shock. Another vertical line is drawn on the smoked plate; and, by repeating the experiment, a number of vertical lines can thus be drawn. Suppose we put a weight in the scale-pan F below the frame, the height of the line drawn on the smoked plate, making allowance for the increased amplitude of the movement obtained by the lever, will indicate the work done by the muscle in lifting the weight. We will see by and by that a muscle not only may do