A text-book of physiology for students and physicians / by William H. Howell.

  • Howell, William H. (William Henry), 1860-1945
Date:
1910
Catalogue details

Licence: In copyright

Credit: A text-book of physiology for students and physicians / by William H. Howell. Source: Wellcome Collection.

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    of the dim bands increases at the expense of the material in the light bands.* As shown in the schema given in Fig. 3, the band exhibiting the property of double refraction seems, during the phase of contraction, to absorb or imbibe material from the isotropic substance constituting the so-called light band. This observation, if beyond doubt, would have the greatest signifi- cance in revealing the location and mode of action of the real contractile material of the fibers. It has, however, been called into question by recent work (see p. 75). The Extensibility and Elasticity of Muscular Tissue.—Muscular tissue, when acted upon by a weight, extends quite readily, and when the weight is removed it regains its original form by virtue a b Fig. 4.—a, Curve of extension of a rubber band, to show the equal extensions for equal increments of weight. The band had an initial load of 17 gms., and this was increased by increments of 3 gms. in each of the nine extensions, the final load being 44 gms. The line joining the ends of the ordinates is a straight line. 6, Curve of extension of a frog’s muscle (gastrocnemius). The initial load and the increment of weight were the same as with the rubber. The curve shows a decreasing extension for equal increments. The line join- ing the ends of the ordinates is curved. of its elasticity. In our bodies the muscles stretched from bone to bone are, in fact, in a state of elastic tension. If a muscle is severed by an incision across its belly the ends retract. The extensibility and elasticity of the muscles add to the effective- ness of the muscular-skeletal machinery. A muscle that is in a state of elastic tension contracts more promptly and more effec- tively for a given stimulus than one which is entirely relaxed. Moreover, in our joints the arrangement of antagonists—flexors and extensors—is such that the contraction of one moves the bone against the pull of the extensible and elastic antagonist. It would seem that the movements of the skeleton must gain * Biedermann, “Electro-physiology,” vol. i, translated by Welby, and Engelmann, “Arcliiv fur die gesammte Physiologie, ” 18, 1.