1881.] the Slriation of Voluntary Muscular Tissue. 



363 



Now, this last-named and important discovery of Bowman's has, 

 I believe, completely been lost sight of, for no mention of it can be 

 found in any modern monograph nor in any systematic text-book that 

 I have examined. The striking points in the paper and in the figures 

 he gives, is the splitting up of the fibre into transverse discs and the 

 demonstration of the sarcous elements as before quoted. This, 

 together with the sarcolemma, everyone connects with the name of 

 Bowman. Modern investigators have worked mostly at the cross 

 striping of muscle, and have found it more complicated than Bowman 

 described, owing, no doubt, to the use of better glasses ; while he 

 explained the phenomenon as due simply to the shape of the fibres — 

 believing, however, probably that it was due also to structural 

 differences — modern investigators have introduced hypotheses to 

 account for it, which imply differences of structure along the filament. 

 The reason of this is, if I may express an opinion, that his theory has 

 been completely lost sight of, and that it was followed by the discovery 

 of startling facts, which at first sight seemed to set it on one side. 



In discussing the views of modern inquirers, I shall not, in all 

 cases, consider them in the order of their priority, and allusion will 

 not be made to much that has been written upon this subject, which, 

 indeed, may safely be put on one side. 



The light stripe — dark stripe of Bowman — has been shown by 

 Dobie, Busk, and Huxley to be traversed by a very fine dark band, or 

 rather line, " Querlinie," dividing it into two equal parts. We shall 

 speak of this as Dobie's line, or the dark stripe in the centre of the 

 light. (Fig 1, D, Plate 5.) Then, again, the dark stripe is traversed 

 in its centre by a lighter band called Hensen's stripe.* (Fig. 1, H, 

 Plate 5.) Other bands border this stripe, but as they are certainly 

 not to be seen in all specimens however well prepared, and as we shall 

 presently account for them, they need not trouble us here. 



As early as the year 1839, Boeck showed that muscle refracts light 

 doubly, which statement was, however, modified in 1857 by Briicke. 

 The latter examined muscles prepared in alcohol by polarised light, 

 and found that the dark stripe (dark in ordinarily non-polarised 

 light) appeared luminous in the dark field of the microscope, and 

 that the light stripes were dark when the Nicols were crossed. The 

 dark stripes, therefore, appeared to be doubly refracting (aniso- 

 tropous), and the light stripe singly refracting (isotropous), the fibre 

 consisting of singly and doubly refracting discs alternating one with 

 another. These observations he verified by an examination of the 

 fibre with thin plates of selenite and mica. The views of Briicke 

 have, in their turn, received considerable modifications which will be 

 understood by reference to a diagram. Fig. 2, Plate 5, expresses 



* This stripe was also described by Dobie in the "Annals of Natural History" 

 for 1849, and it may be called " Dobie's light stripe." 



