1881.] 



the Striation of Voluntary Muscular Tissue. 



371 



parallel, rays of light are passing through the fibre, by using con- 

 verging or diverging rays the appearance will be altered, and it will 

 be possible by careful adjustment of a lens to cause a total reversal of 

 the striping. If a fibre be carefully focussed and a strong biconcave 

 diverging lens be placed between the stage of the microscope and the 

 mirror, and carefully moved about with the fingers, it will be possible 

 entirely to alter the fibre, causing a total reversal of the cross bands. 

 On withdrawing the lens, of course the fibre resumes its normal ap- 

 pearance. I may mention that several lenses were tried before one 

 was found which would in at all a satisfactory manner show this phe- 

 nomenon ; when successful the experiment is very striking. 



In opposition to my view is the one generally accepted, namely, 

 that the cross stripings are produced by differences along the fibre of 

 chemical composition, and refrangibility. 



Now, suppose that there were along the fibre two alternating struc- 

 tures, A and B. Let A represent the bright stripe and B the dark 

 stripe. If A has a higher or lower refractive index than B, it is 

 evident that although they were immersed in any number of fluids of 

 refrangibility varying from the lowest to the highest, yet A would 

 always be distinguishable from B, and the striping would always be 

 apparent. Then, again, by placing the fibres in fluids of indices near 

 to that either of A or B, the more striking would be the contrast. If, 

 however, the fibre were homogeneous throughout, the striping being 

 nearly due to the form, then if the fluid and the fibre have the same 

 refractive index all striping will disappear. On Professor Tait's 

 suggestion, I tried a series of fluids formed by mixing, in various pro- 

 portions, alcohol, whose refractive index is low, with oil of cassia, which 

 is high. In this way I have prepared specimens showing almost no 

 cross striae, the fibre appearing uniform until after most careful 

 examination. 



Dr. Klein has since shown me some muscular fibres of an insect. 

 They were quite smooth and cylindrical, and were unstriated. In these 

 specimens there were, on very close examination, cross lines separated 

 by comparatively wide intervals. It is possible that they represented 

 Dobie's lines.* 



But it may well be asked, What about the action of staining agents, 

 such as logwood, which is stated to tint the dark stripe and Dobie's 

 line ? Does this not show a difference of structure along the fibres ? 



Once having the clue it will be understood that just as the unstained 



* More recently my friends Messrs. Greddes and Beddard have demonstrated a very 

 curious condition in the muscular fibres of the Echinus, which my views entirely 

 explain. They noticed that in the same fibre some parts were cross striped, while in 

 parts no striation was to be seen. Hearing of my explanation of the markings, they 

 re-examined their specimens (which I have also seen), and found that when the striae 

 were visible there, and only there, the fibre was ampullated. (See fig. 5.) 



