. Elements of human physiology. Physiology. 122 PHYSIOLOGY nerve prei^aration, to a galvanometer. We shall then obtain a deflection of the mirror of the magnet, due to the current of rest or demarcation current. If now the nerve be stimulated with an interrupted current so as to throw the muscle into a tetanus, the ray of light from the galvanometer mirror is observed to swing back towards the zero of the scale, showing that the current which was present before is diminished. When the excitation of the nerve is discontinued, the galvano- meter indicates once more the original current of rest.
. Elements of human physiology. Physiology. 122 PHYSIOLOGY nerve prei^aration, to a galvanometer. We shall then obtain a deflection of the mirror of the magnet, due to the current of rest or demarcation current. If now the nerve be stimulated with an interrupted current so as to throw the muscle into a tetanus, the ray of light from the galvanometer mirror is observed to swing back towards the zero of the scale, showing that the current which was present before is diminished. When the excitation of the nerve is discontinued, the galvano- meter indicates once more the original current of rest. Thifi diminution of the current of rest during activity of a muscle is spoken of as the * negative variation.'' In carrying out this experiment it is usual to compensate the demarcation current by sending in a small fraction of the current from a constant cell. The arrangement of the apparatus is represented in the accompanying dia- gram. Two non-polarisable electrodes (np) are applied to the surface and Fig. cross-section of a muscle (m). These are connected with the shunt of the galvanometer, one of the wires however being connected with a Pohl's re- verser (p), and this in its turn with the shunt (s). The two end terminals of the reverser are connected with a rheochord, through the wire of which (a, b) a constant current is passing from the Daniell cell (d). By means of the rider (c) the fraction of current passing through the reverser can be modified to any extent. The key (k) being open, the muscle is connected with the shunt and galvanometer, and the direction and extent of the swing noticed. The key (k) is then closed, and by means of the reverser the current is sent through the galvanometer in the opposite direction to the demarcation current, and the rider (c) shifted until the two currents exactly balance each other, and the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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