Elements of human physiology (1907) Elements of human physiology elementsofhumanp05star Year: 1907 124 PHYSIOLOGY thus giving rise to a momentary current in the secondary coil, s, and ex- citing the muscle, m. In the same way the brushes, b, close the galvano- meter-electrode-uiuscle circuit, g, t, b, t', 1, ii, ([, each time they brush on the copper banks, t t'. By turning the disc, a, round, the interval at which the brushes, b, pass t t', after the brushes, a, pass r r', can be altered at will, and therefore the interval between stimulation and leading off the current to the galvanometer.
Elements of human physiology (1907) Elements of human physiology elementsofhumanp05star Year: 1907 124 PHYSIOLOGY thus giving rise to a momentary current in the secondary coil, s, and ex- citing the muscle, m. In the same way the brushes, b, close the galvano- meter-electrode-uiuscle circuit, g, t, b, t', 1, ii, ([, each time they brush on the copper banks, t t'. By turning the disc, a, round, the interval at which the brushes, b, pass t t', after the brushes, a, pass r r', can be altered at will, and therefore the interval between stimulation and leading off the current to the galvanometer. But there is no need for any demarcation current to be present in order to show an electrical change accompanying contraction. In fact we learn much more about the nature of the excitatory change if we study the electrical behaviour of a perfectly normal (and therefore currentless) muscle on stimulation. This can be easily done by means of the rheo- tome or capillary electrometer. If a perfectly miinjured regular muscle (such as the sartorius) be stimulated with a single induction shock at one end (x) (Fig. 56), and the relative electrical conditions of the Fig. 56. Diagram showing diphasic variation of uninjured muscle. points (a) and (b) investigated, it will be found that as soon as the excitatory process reaches (a), this point becomes negative to (b), and there is thus a current in the galvanometer from (b) to (a). A moment later the two points are equipotential, as shown by the fact that no current passes through the galvanometer. A thousandth of a second later this balance is upset, and now (b) is negative to (a), and the galvano- meter needle swings in the opposite direction. Thus every excitation of a normal muscle gives rise to a diphasic variation, of such a direction that the point stimulated first becomes negative ' to all other points of the ' The statement that the excited portion of the muscle becomes ' negative,' though sanctioned by long usage, is not very
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