MUSCULAR MOTION. 



523 



ing of tlie material composing the fibre, as is 

 shown by the general outline of the part, but 

 especially by the appearances visible in its 

 interior. The transverse stripes, both light and 

 dark, become longer and thinner; in other 

 words, the discs expand in circumference, 

 flatten and approximate to one another; or to 

 use another form of expression, the fibrillae 

 become shorter and thicker, both in the par- 

 ticles composing them and the material con- 

 necting those particles (Jig. 301). 



Fig. 301. 



Fragment of an elementary fibre (from the eel) partially 



contracted in water. Magnified 300 dittiii, 



a, uncoutractcd part. 



b, contracted part, along the border of which, at 



c, c t the sarcolemma is raised from the surface 

 by the water that has been absorbed, that has 

 thereby caused the contraction, and by it has been 

 expelled from the contractile mass. 



These changes are always local, or partial, 

 and it is most evident from the characters they 

 constantly present, that they are not limited to 

 any determinate regions, points, or segments, 

 but occur indifferently wherever the exciting 

 cause may chance to be exerted. Neither discs 

 nor fibrillae appear to have the smallest share, 

 as aggregatiotis of particles bearing those par- 

 ticular forms, in producing the phenomena of 

 contraction. A contraction is never bounded 

 to a particular number of discs or fibrillas, and 

 is never accurately limited by the interval 

 between two discs. It constantly happens that 

 at the edge of the contracted part several discs 

 are only partially engaged in it. A contraction 

 generally, when commencing at the broken 

 end of a fibre, occupies its whole width there; 

 but when it commences at the border of the 

 fibre it may be confined to a portion of many 

 discs. And, further, a contraction never occu- 

 pies the whole length of a fibre or fibrilla at 

 once. A contraction excited in an elementary 

 fibre by the contact of a hair extends into the 

 mass equally in all directions, as we might 

 suppose it would do, if the mass were homo- 

 geneous. 



In a word, an attentive study of these inte- 

 resting phenomena has convinced me that in 

 the bare fact of contraction the build of the 

 fibre is an item of no importance whatever : the 

 exquisite symmetry displayed in the apposition 

 of its component particles is, as it were, dis- 

 regarded and overlooked, while the whole pro- 

 cess is to be referred to the material itself, the 

 ultimate tissue, whose property is contractility. 

 This property appears to reside both in the par- 

 ticles and the substance connecting them. 



The ultimate movements, therefore, on which 

 contraction depends, whatever they may con- 

 sist in, are molecular, and far beyond the reach 

 of sense. 



It will be perceived that this view of the 

 subject is the only one which can harmonize 

 the fact of contraction in voluntary muscle 

 with the same phenomenon in structures which 

 have no complicated internal arrangement of 

 particles. In regarding contractility, therefore, 

 as a property of the living muscular fibre in 

 general, it is meant that it resides in it as a 

 property without which it would not be muscle, 

 and in such a manner that no particle, how- 

 ever microscopic, can be detached from muscle 

 which does not of itself, and independently of 

 the rest, possess this property, as long as it 

 possesses vitality. 



It follows from what has been advanced that 

 those hypotheses which refer contraction to a 

 force exerted between determinate but distant 

 points of the fibre, as where the nervous fibrillae 

 cross it, or at intervals such as Muller* has 

 sometimes seen in insects, must fall to the 

 ground. They are so entirely incompatible 

 with the facts above stated that it can scarcely 

 be necessary to dwell at length on the other 

 reasons for rejecting them, or on the explana- 

 tion of the phenomena adduced in their support. 

 The main fact on which they have been built 

 is that long ago mentioned by Hales, and more 

 recently studied with minute care by Prevost 

 and Dumas, viz. that in the abdominal muscles 

 of the frog detached and excited by galvanism, 

 the elementary fibres are seen to be thrown 

 more or less into a zig-zag form. It is evident 

 that in interpreting what they saw these eminent 

 physiologists mistook the relaxed fibres for 

 contracted ones. In conducting such experi- 

 ments many precautions are required, and at 

 the best, nothing of the real process of contrac- 

 tion can be witnessed. As Muller correctly 

 remarks, the muscle is too thick to be seen 

 under a high power. Besides, the shock of 

 galvanism causes only an instantaneous con- 

 traction, during which the muscle is so agitated 

 that it is in vain to attempt to examine its con- 

 dition. It gets out of the focus of the instru- 

 ment. What is seen afterwards is not the 

 contraction but its result, viz. an approximation 

 of the extremities of the fibres. If the galvanic 

 shock has acted uniformly on all the fibres 

 (which is rare), they all remain straight; but if 

 on a part only, those which have escaped con- 

 traction are thrown into zig-zags by having their 

 ends brought nearer through their cellular con- 

 nexion with neighbouring contracted fibres. It 

 is most natural that the precise point of such 

 flexures should often be determined by the 

 passage of nerves or vessels across the fibres. 

 This is corroborated by the circumstance that 

 relaxed fibres fall at once into zig-zags when 

 their ends are made to approach by mechanical 

 means. 



MM. Prevost and Dumas have themselves 

 drawn attention to an example of shortening 

 without zig-zags in the case of the distended 

 abdominal muscles of the female frog before 

 spawning. They found that the fibres of those 

 muscles when cut across remained straight, 

 after shortening from 145 to 107 millimetres. 



* Physiology by Baly, p. 889. 



