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.
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![I'ig. 113. Elastic after-action of frog's muscle (see text). der. The abscissal line previous to stretching (a) has been prolonged as a dotted line to indicate its relation to the elastic curve. A vv^eight of 100 grammes was ap- plied to the muscle at h, and removed at d after the lapse of a minute. At h there is a sudden extension, followed by a slow after-extension (c). At d there is a sudden shortening, followed by a slow after-shortening (e), which does not, however, raise the abscissal line (/) to the level of the first abscissa (a), because the muscle had been over-stretched; c and e are the two phases of the elastic after^action. Muscular Tonicity.—Even in their relaxed condition the muscles are in a state of slight tension, termed their tonicity, in consequence of which they feel firm and not flabby. In virtue of this condition, a muscle retracts when it or its tendon is divided, and the wound gapes, although the muscle is in a state of relaxation. This muscular tone has been ascribed to a slight contraction of the muscle, but there is no evidence that it is due to anything more than its elasticity. Were it due to con- traction it ought to disappear when the nerve of the muscle is divided; but section of the nerve is not immediately followed by the slightest elongation of the muscle (Heidenhain, Op. 49, 1856), although in course of time, apparently owing to impaired nutrition, the tonicity does dis- appear. The so-called tone of the sphincters of the anus and bladder is not an elastic effect, but a real contraction kept up by nervous impulses passing from the spinal cord. Observations by Bonders and Mansvelt [Op. 78) on the human biceps, and by Koy {Op. 2, i. 472) on the frog's heart, show that the elasticity of muscle is diminished by fatigue. Eoy's experiments also prove that it is diminished by defective nutrition. Continued diminution of the elasticity of the cardiac fibres ends in their permanent exten- sion, and the serious pathological condition of cardiac dilatation is the result. The elasticity of muscle is also diminished in weak and relaxed conditions of the system. A flabby state of the tongue is a sign of it. At death the elasticity increases in amount, but becomes less per- fect; the muscles are therefore less extensible, and, when stretched, recoil less perfectly. E. Weber {Op. 75) found that if the same weight be applied to a muscle during its states of relaxation and contraction, it produces a relatively greater extension in the contracted muscle ; from which he inferred that during contraction elasticity is dimin- ished. He further stated that, if a muscle be stretched by a weight so heavy that it cannot contract, a slight elongation occurs when the muscle is stimulated ; from which he inferred that the altered elasticity is due to a molecular change induced by stimula- tion. Weber's method of experimenting was rough, and probably for that reason the latter observation has been found by Wundt {Op. 77, p. 574) to be incorrect. There is therefore no evidence of any change in the elasticity during the active condition of muscle.- This conclusion is au]>ported by Kronecker and by Bonders. The greater extension produced by a weight in a contracted as compared with a relaxed muscle, appears to be owing to a diminished shortening of the muscle during contraction, because of the re.sistance offered by the weight.](https://iiif.wellcomecollection.org/image/b21981747_0153.jp2/full/800%2C/0/default.jpg)
