A text-book of physiology, for medical students and physicians . c) bands at restand in contraction, as seenby ordinary and by polar-ized light. The figure rep-resents a muscle fibril(beetle) in which the lowerportion has been fixed in acondition of contraction.—{Engelmann.) 20 THE PHYSIOLOGY OF MUSCLE AND NERVE. of the dim bands increases at the expense of the material in thelight bands.* As shown in the schema given in Fig. 3, the bandexhibiting the property of double refraction seems, during thephase of contraction, to absorb or imbibe material from theisotropic substance constituting the s
A text-book of physiology, for medical students and physicians . c) bands at restand in contraction, as seenby ordinary and by polar-ized light. The figure rep-resents a muscle fibril(beetle) in which the lowerportion has been fixed in acondition of contraction.—{Engelmann.) 20 THE PHYSIOLOGY OF MUSCLE AND NERVE. of the dim bands increases at the expense of the material in thelight bands.* As shown in the schema given in Fig. 3, the bandexhibiting the property of double refraction seems, during thephase of contraction, to absorb or imbibe material from theisotropic substance constituting the so-called light band. Thisobservation, if beyond doubt, would have the greatest signifi-cance in revealing the location and mode of action of the realcontractile material of the fibers. It has, however, been calledinto question by recent work (see p. 75). The Extensibility and Elasticity of Muscular Tissue.—Musculartissue, when acted upon by a weight, extends quite readily, andwhen the weight is removed it regains its original form by virtue am ——? Hi. Ffa. 4.—a, Curve of extension of a rubber band, to show the equal extensions for equalincrements of weight. The band had an initial load of 17 cms., and this was increasedby increments of :} urns, in each of the nine extensions, the final load being 44 gms. TheIn;, joining the ends of the ordinates is a straight line, b, Curve of extension of a frogstun cle gasf rocnemius). The initial load and the increment of weight were the same as withthe rubber. The curve shows a decreasing extension for equal increments. The line join-ing the <*ri< I -^ of the ordinates is curved. of its elasticity. In our bodies the muscles stretched from boneto bone are, in fact, in a state of elastic tension, [f a muscle issevered by an incision across its belly the ends retract. Theextensibility and elasticity of the muscles add to the effective-of the muscular-skeletal machinery. A muscle that is in astate of elastic tension contracts mo
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