Page:Life in Motion.djvu/151

 LECTURE V Source of muscular energy— Food stuffs— Milk— Muscle as an engine— Repair of muscle— Ratio of mechanical energy and heat— Fatigue of muscle— Athletics.

beginning this lecture, I will show you an experiment which Professor du Bois Reymond calls the muscle dance. You see the muscle connected with the interrupter (see Fig. 11, p. 30), so that when it contracts it breaks the primary circuit of the induction coil and also rings the electric bell. On the scale-pan below the interrupter, I have placed a heavy weight, which at once stretches the muscle when it begins to relax. The relaxation of the muscle, however, again closes the primary circuit, and the muscle receives a shock from the secondary coil. This again causes it to contract and to ring the bell. Again it relaxes and gets another shock. Thus the muscle breaks the circuit by its contraction,