Volume 1

A textbook of pharmacology, therapeutics and materia medica.

  • Brunton, T. Lauder (Thomas Lauder), 1844-1916.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: A textbook of pharmacology, therapeutics and materia medica. 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.

    196/816 (page 140)
    more slowly in involuntary than in voluntary muscle; and its rate in the involuntary muscle of the heart, though slower than in ordinary striated muscle, is quicker than in unstriated muscle, so that in this respect the heart is intermediary between the two.1 The passage of contraction waves in involuntary muscular fibre is affected by the same conditions as voluntary muscle, the conduction of the contractile wave being rendered slower by fatigue and cold, while it is quickened by heat. Cold and fatigue also render the rhythmical pulsations smaller and longer, while heat has an opposite effect. The passage of the contraction wave may also be diminished or arrested by section or pressure, just as in the contractile tissue of medusae,2 so that instead of each contraction wave passing the block pro- duced by the sections or compression, only one out of several, or none at all, may pass. The proportion passing the block depends upon its completeness. If the tissue forming the bridge be dry as well as narrow, the block becomes more com- plete, and may be again diminished by moistening. Variations in the strength of the stimulus do not affect the passage of the contraction wave over the block, so that it would appear that the injury caused by the section, along with the narrowing of the conduction path, retards the re-establishment of the conductive power. In experiments made upon the heart of a tortoise cut into a strip, it has been found by Gaskell that stimulation of the vagus removes the block, quickens the recovery of the tissue, and causes every contraction wave to pass. The effect upon the muscle therefore seems to be trophic. A weak interrupted current applied to the muscle directly has the same action as stimulation of the vagus, i.e. it increases the conducting power of the muscle. Sometimes, however, both the vagus and a weak interrupted current have an opposite effect, and diminish instead of increasing the conducting power. An artificial rhythm may be induced in a strip of involuntary muscular fibre cut from the heart of the tortoise by passing a weak interrupted current through it and then stimulating it at one end by induction shocks, at intervals of about five seconds. After a while, if the induction shocks are discontinued, the muscle still continues to contract rhythmically at the same rate. These con- tractions, at first weak, afterwards become strong, and may last for many hours. Both the conducting and the contractile power of the muscle are diminished by muscarine. When a strip of it is stimulated by induction-shocks applied to one end, the con- traction wave passes quickly along; but muscarine appears to 1 Hermann's Handbuch d. Physiologic, Bd. 1, p. 56. 2 Engelmann, Pflilgcr's Archw, 1875, Bd. il, p. 465; Gaskell, Journal of Physiology, vol. iii. p. 367.