A textbook of experimental physiology for students of medicine / by N.H. Alcock and F.O'B. Ellison ; with a preface by E.H. Starling.

  • Nathaniel Henry Alcock
Date:
1909
Catalogue details

Licence: In copyright

Credit: A textbook of experimental physiology for students of medicine / by N.H. Alcock and F.O'B. Ellison ; with a preface by E.H. Starling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    INJUEY - AND ACTION CUEEENTS essential that the contacts with the tissue shall give no current themselves. Hence non-polarisable electrodes are invariably used. These consist of a terminal of amalgamated zinc, dipping into a saturated solution of zinc sulphate contained in a small glass tube; the end of the tube applied to the tissue is closed by a plug of kaolin moistened with salt solution. Demonstrations.—Set up the circuit as in Fig. 13. Dissect out a gastrocnemius-sciatic preparation with as little injury to the muscle as possible. Place one electrode on the belly of the muscle, the other on the tendon, contact being made through linen threads moistened with salt solution. The s Fig. 13.—Injury current and negative variation of muscle, s, switch-board; p, preparation circuit; m, the muscle; t, its injured end ; n, its nerve; the arrow shows the direction of the injury current in the muscle; g, galvano- meter circuit; g„ the galvanometer ; s„ the shunt; c, compensation circuit; r and r, resistances ; Exc, exciting circuit. more carefully the preparation is made the less will be the current, and the inference is that resting uninjured tissue is iso-electric. The tendon end of the muscle is then touched with a hot wire, and the electrode reapplied. There is now a very marked- difference of potential, the 'current of injury.' The direction of this current is, in the tissue from the injured to the uninjured part, through the galvanometer from the uninjured to the injured part. Hence the injured part is said to be galvano- metrically negative to the uninjured, or electro-positive. As the injured part behaves as regards its differences of potential like
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