Page:Life in Motion.djvu/190

170 that a current is now flowing in the opposite direction. This swing backwards will carry the galvanometer needle to the point from which it started, or even to the opposite side. It is known technically as the negative variation of the uscle current; and careful experiment has shown that it is not due to a mere diminution of the current from the muscle while the muscle is at rest, but that it is really a current in the opposite direction; that is to say, when a muscle having a cross section contracts, the surface of the cross section becomes positive instead of negative, and the longitudinal surface becomes negative instead of positive. As a current always travels from positive to negative, it follows that the current in a contracting muscle travels in the opposite direction from its course in a resting muscle.

Other tissues than muscle show so-called resting currents, and when the tissue acts or responds to a stimulus, there are strong indications that a negative variation current is produced. Thus a nerve shows the same phenomena as a muscle. Currents have also been observed in glands.