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Mr. J. B. Haycraft. Upon the Cause of [Feb. 3, 



strate its existence, and giving figures of it, which have been 

 copied into most modern histological works. The nuclei of the sarco- 

 lemma he also figured, but what most concerns us is his description 

 of the cross striation. Bowman, I believe, first pointed out that not 

 only can a fibre be split up longitudinally into fibrillae along certain 

 dark lines which may generally be seen, even in fresh preparations, 

 but that it splits up transversely along the dark stripes. Each 

 fibrilla may, therefore, be split up into tiny segments across the dark 

 striae. " On the whole, little doubt remains in my mind that the 

 fibrillae consist of a succession of solid segments or beads connected by 

 intervals generally narrower, and I believe the beads to be light, and 

 the intervals the dark spaces when the fibrilla is in exact focus." 

 His idea of a fibre naturally follows from that just given of a fibrilla, 

 and, quoting again from him, we find " a fibre consists of sarcous 

 elements (so he termed the little segments or beads) arranged and 

 united together endways and sideways, so as to constitute in these 

 directions respectively fibrillae and discs, either of which may in 

 certain cases be detached as such," and " the dark longitudinal striae 

 are shadows between fibrillae, the dark transverse striae shadows 

 between discs." 



It will be seen that in one particular Bowman disagreed with 

 Schwann and the older writers, and at the same time with those of 

 more recent date. According to him, the bead was light and the 

 constriction dark, when the muscle was in exact focus, a description at 

 variance with everyone. In the same paper he mentions this 

 remarkable fact, that on altering the focus the stripes were reversed ; 

 he must have examined it — this bears in a most important way on 

 our investigations, to be afterwards described — in the reverse focus of 

 what it is ordinarily figured in. His view of the form, and the split- 

 ting of the fibre, was probably correct, for he described the cleavage 

 as occurring in the narrow part, which appeared to him, focussing as 

 he did, to be dark, and indeed it is often difficult to say which it is, 

 whether dark or light, for, as I shall more particularly mention 

 afterwards, the slightest alteration of the focus is sufficient to reverse 

 the appearance of the fibre. Bowman, moreover, accounted for these 

 light and dark parts of the fibrillae, comparing a muscular filament 

 to a glass rod with alternate swellings and depressions, which, when 

 viewed with transmitted light, gives just the same appearance, 

 and from a study of his paper, although it is here somewhat indefi- 

 nite, I judge that he concluded the moniliform shape to be a cause of 

 the striping.* 



* Bowman, nevertheless, seems to consider the dark stripe of a different structure 

 from the light, not so much from the shading, but from the transverse cleavage. 

 He is not quite definite here, but this is the impression I have gained from a careful 

 perusal of his paper. 



