CHANGE IN SHAPE DURING MUSCULAR CONTRACTION 51$ 



tion. These are, of course, wholly passive and would occur equally well if 

 we should lift the weight to the height of the contraction, then simply let it 

 fall while taking a record. 



Change in Shape during Muscular Contraction. There is a consider- 

 able difference of opinion as to the mode in which the transversely striated 

 muscular fibers contract. The most probable account is that the contraction 

 is effected by an approximation of the constituent parts of the fibrils, which, 

 at the instant of contraction, without any alteration in their general direction, 

 become closer, flatter, and wider, a condition which is rendered evident by 

 the approximation of the transverse striae seen on the surface of the fasciculus, 

 and by its increased breadth and thickness. The appearance of the zigzag 

 lines into which it was supposed the fibers are thrown in contraction is due 

 to the relaxation of a fiber which has been recently contracted and is not 



FIG. 323.' The Microscopic Appearances During a Muscular Contraction in the 

 Individual Fibrillae, after Engelmann. i. A passive muscle fiber; c to d = doubly refractive 

 discs, with median disc a & in it; h and g are lateral discs;/ and e are secondary discs, only 

 slightly doubly refractive; figure on right same fiber in polarized light. The bright part 

 is doubly refracted, black ends not so. 2. Transition stage. 3. Stage of entire contrac- 

 tion. In each case the right-hand figure represents the effect of polarized light. (Landois, 

 after Engelmann.) 



at once stretched again by some antagonist fiber or whose extremities are 

 kept close together by the contractions of other fibers. The contraction is 

 therefore a simple and, according to Edward Weber, a uniform, simultaneous, 

 and steady shortening of each fiber and its contents. What each fibril or 

 fiber loses in length, it gains in thickness. The contraction is a change of 

 form, not of size; it is, therefore, not attended with any diminution in bulk 

 from condensation of the tissue. This has been proved for entire muscles 

 by making a mass of muscles, or many fibers together, contract in a vessel 

 full of water, with which -a fine, perpendicular, graduated tube communi- 

 cates. Any diminution of the bulk of the contracting muscle would be 

 attended by a fall of fluid in the tube, but when the experiment is carefully 

 performed, the level of the water in the tube remains the same, whether the 

 muscle be contracted or not. 



In thus shortening, muscles appear to swell up, becoming rounder, more 

 prominent, harder, and apparently tougher. But this hardness of muscle in 

 the state of contraction is not due to increased firmness or condensation of the 

 muscular tissue, but to the increased tension to which the fibers, as well as 



