1881.] the Striation of Voluntary Muscular Tissue. 367 



the fibre. This is, however, purely an assumption which in no way 

 follows. 



We can also account for all these cross markings in a way which 

 involves no theory, and requires for its appreciation but a knowledge 

 of most elementary geometrical optics. 



If a small fragment of muscle be teazed out in water, salt solution, 

 or almost any other fluid, and examined in the ordinary way, with a 

 power of 300 diameters or more, the important fact may be made out 

 (which is the basis of all my future observations), that the borders of 

 the fibres are not smooth, but undulate, presenting wavy margins. 

 (Kg. 1.) 



In the fresh unstained preparation there is a halo around the edge 

 of the fibre which masks the crenulated border, yet by carefully adjust- 

 ing the mirror so as to obtain oblique light, or by searching for a fibre 

 partly in the shade of another, this may always be made out ; in the 

 case of insects' muscle, this is, however, always easy to demonstrate, 

 for the fibres are much coarser, indeed, the appearance has been often 

 figured in the works even of recent histologists. If the preparation 

 be stained by any of the ordinary dyes, perhaps most readily by picro- 

 carmine, the border is in all cases very distinct, and the regularly 

 sinuous margin is unmistakeable. Now, what is the significance of 

 the wavy outline ? It is, as will readily be understood, that the fibre 

 is ampullated, the wavy outline being but the optical expression of 

 such a figure. A muscular fibre is then not a smooth cylinder, but is 

 like the turned leg of a chair, or like the transversely ribbed neck of a 

 common water-bottle in shape. If the fibre be broken up into 

 fibrillae, which is very easy, after maceration in alcohol, these are seen 

 to have just the same characters, indeed, a small bundle of fibrils is 

 most convenient for study. It may be well to remark, that the ulti- 

 mate fibrillee often show but little cross marking, and appear almost 

 smooth ; that is, however, only due to their small size ; a good lens 

 will bring out both points. 



The above-described appearances may be observed in all the varieties 

 of muscle that I have as yet examined, e.g., those obtained from man, 

 the dog, cat, rabbit, guinea-pig, mouse, frog, mussel, crab, bee, wasp, 

 Dytiscus, Hydrophilus, common house fly, &c, &c. 



The transverse stripings of the fibre are related to and correspond 

 with the inequalities of the surface. (Fig. 1.) The little elevations at 

 the borders correspond, of course, to the little ridges which run round 

 the fibre, while the dips at the borders are the optical expressions of 

 little valleys running between them. In the ordinary position, the dark 

 stripe marks the position of the ridge, and the light stripe lies in the 

 little valleys, as will be seen on reference to fig. 1, Plate 5. 



Then, again, Dobie's line (Krause's membrane), which is a faint 

 dark band in the very centre of the bright stripe, runs along the 



