A text book of physiology / by William Rutherford.

Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: A text book of physiology / by William Rutherford. Source: Wellcome Collection.

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

    156/180 (page 144)
    ■when it enters and when it leaves the nerve, but not during the period of its flow unless it undergo variations of intensity (Du Bois Eeymond). It will be afterwards shown, however, that the vital properties of the nerve are affected during the entire period of flow. But when the peripheral terminations of sensory nerves—e.g. those of the skin or tongue—are traversed by the stream, they are stimulated during the entire period of flow as well as at the moments of entrance and departure. The result is a constant pricking and burning sensation in the case of the skin, and a metallic taste, with a burning and pricking sensation, in that of the tongue. Muscular fibres are aflected in the same sense as the peripheral sensory nerve terminations. Thus, on stimulating a muscle directly with a galvanic stream just strong enough to give a re- action, contraction occurs at the closure and opening of the circuit; but on increasing the strength of the current, a state of constant contraction (tetanus) ensues. The reaction of the muscle is therefore for the most part similar to that of peripheral sensory nerve terminations, and the question arises. Is the muscular reaction due to a dii-ect eff'ect on the muscular fibres, or on the terminations of the motor nerves, or on both ] The question can be partially answered by physiologically eliminating the nerve terminations tlirough the paralysing influence of curara. Tliat this poison really does paralyse the nerve-ends must be assumed until the proof is furnished and explained (p. 151). The curarised muscle requires a somewhat stronger current, but the reactions given both by the weak and stronger currents are similar to those of the non-curarised muscle. Therefore the eff'ect of a galvanic current on muscular fibres differs from its effect on nerve fibres, and resembles that on peripheral sensory nerve terminations. Whether or not the motor nerve terminations are affected in a manner similar to the sensory nerve terminations is as yet unknoM'n. In both nerve (Pfliiger, Op. 81, p. 453) and muscle (Von Bezold, Op. 82, p. 266) stimulation occurs only at the — pole (cathode^) when the circuit is closed, and only at the + pole (anode) when it is opened. This may be readily shown by laying a curarised frog's sartorius upon a pair of non-polarisable electrodes, with a considerable length of fibres between them. In a curarised muscle the transmission of excitement is delayed because of tlie nervous paralysis, and it may be observed, especially when the muscle is fatigued, that, on closing the circuit, a contraction wave appears at the cathode and rapidly travels along the muscle, while at opening the wave begins at the anode. The use of a magnifying glass is of service in this experiment. If the muscle be partially cut across between the electrodes, the cut may be seen to gape towards the — pole at closing, and towards the -|- pole at opening the circuit (Engelmann, Op. 83, p. 340 ; Romanes, Op. 1, x. 730). The effect of an electrical current on muscle is most powerful when it is sent along the fibres. b. Stimulation by Faradic Electricity is the most common method of excitement in physiological experiments, because of the readiness ^ Cathode, from Kara and 6S6s, a downward way. Anode, from dvd and 656s, an upward way. These terms, commonly applied respectively to the - and + poles of the electrical circuit, indicate the direction of the + stream to and from the battery.