154 LOCOMOTION. [CHAP. vn. 



the fibre in syrup. But the point of greatest interest is as to the 

 nature of the markings on the individual fibrillse or discs. It is unsafe 

 to come to a conclusion on this question from any appearances seen 

 on the entire fibre ; for it is clear that the relative position of the 

 particles may be very easily deranged, and their regularity broken, 

 by the slightest injury to the mass. 



Two appearances commonly present themselves in examining the 

 striped fibres : in some parts the cross stripes are perfectly rectilinear, 

 or, if curvilinear, parallel in their course; in other parts, these stripes 

 do not extend across the fibre, but are more or less interrupted, 

 forming zigzags and enclosing spaces of a great variety of shape and 

 size, in concert with the longitudinal stripes. In such specimens we 

 see the semblance of spirals in almost infinite number and vafiety. 

 The former of these appearances is most seen in large fibres, and 

 where great care has been used not to drag the tissue ; the latter 

 under the reverse circumstances. The former seems on a prima 

 facie view un unmutilated, the latter a deranged condition ; and 

 they may be proved to be so by a further examination. 



For this purpose we should make choice of a fresh fibre which is 

 prone to separate into its individual fibrillse, and which exhibits 

 their outline in the greatest distinctness and beauty.* If fibrillse 

 entirely isolated be now inspected, they will be found to present 

 alternate light and dark points, when the part is a little out of 

 focus. The light parts are the centres of highly refracting par- 

 ticles, acting as lenses ; the dark points, the intervals between them 

 (fig. 3 7, c"). If now the focus be carefully adjusted, and the achro- 

 matic condenser be employed for the purpose of defining the outline 

 with the utmost precision, each dark interspace between the refract- 

 ing points will be found to be reduced to two very slender straight 

 lines, crossing the fibrilla in a perfectly transverse direction, and 

 giving the light spaces, as now seen, a rectangular figure (fig. 37, c'). 

 Now, it is absolutely certain that no spiral arrangement could 

 produce, or even co-exist with, these unequivocal appearances ; but 

 it is not difficult to comprehend how a derangement of the lateral 

 parallelism of these refracting particles should produce an appear- 

 ance of spirals in the fibre, or how two fibrillee running together, 

 but with their particles slightly deranged, should wear the same 

 very deceptive aspect. 



* The fibres of fishes will generally prove better than those of mammalia, 

 because they usually cleave into fibrillae having very sharp and clear outlines ; 

 and those of the salmon, for example, will seldom fail to do so. 



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