1881.] the Striation of Voluntary Muscular Tissue, 



375 



tested all these points by a careful examination of insects' fibres 

 with thin plates of selenite and mica. This method is not so satis- 

 factory, nor do the differences of colour seen give such trustworthy 

 evidence as may be obtained by the crossed Nicols alone. 



The . Fibre during Contraction. — Living insects' muscle may be 

 examined and the changes observed when the waves of contraction 

 pass along the fibre, or perhaps better still, they may be fixed with, 

 osmic acid. The muscles from the leg of an insect are rapidly 

 separated out on a slide, and a drop of weak osmic acid added which 

 kills the fibres instantaneously, fixing them in the position that they 

 happen to be in. On examination one generally finds fibres which, in 

 part of their course are contracted, and in other parts relaxed, when 

 the differences in appearance may readily be studied. It may here 

 be observed that the fibres bulge at the contracted part, so that if the 

 surfaces be examined the focus of the microscope must be ac- 

 commodated. 



The cross stripes are nearer one to another and correspond, as 

 before, with the ridges, and valleys seen at the margin, which are 

 much more prominent and bolder in outline. 



In the Contracted Fibre the Striping is practically the same as in the 

 Stretched Condition. — The contracted fibre exhibits jnst the same 

 reversing of stripes on alteration of focus, and Dobie's line and 

 Hensen's stripe can both be seen in the same positions ' as in the un- 

 contracted muscle, provided the fibre is suitably placed for examina- 

 tion and not sheared in its length. We must entirely deny the common 

 statement, first introduced, we believe, by Merkel and Engelmann, that 

 in the contracted state the bright band becomes the darker. If good 

 specimens of insects' muscle be examined, which have been treated 

 with osmic acid, and if the fibre be not sheared, the valley is always 

 bright in the ordinary or deeper focus. I have verified this point in 

 very many cases. Passing along a fibre from the relaxed end to a 

 part where the contraction is fullest, the appearances vary in degree, 

 but not in kind. The main features are in both cases the same, but 

 the stripes are now narrower, and often it is not so easy to see Dobie's 

 and Hensen's stripes. This follows from the statement of Engelmann, 

 viz., that "the bright stripes become darker than the dim;" for he 

 himself notices that at one point, or phase, in the contraction, no 

 striping is to be made out. We agree with Ranvier that this is not 

 true, indeed it would be impossible for a muscular fibre with its con- 

 figuration not to be marked across its length. 



This subject will call up to the mind of every working histologist, 

 appearances which he must have met with in other fields of research. 

 Many tissues naturally, or after clumsy manipulation, present am- 

 pullations which always co-exist with cross striae. The fibres of the 

 crystalline lens are wavy in outline, and when many of them are 



vol. xxxi. 2 E 



