VOLUNTARY MUSCULAR FIBRE. 137 



tion as that of the fibre. A small amount of granular matter 

 may be seen at their extremities. Cross cuts of fibres show 

 that, with possibly some exceptions, they lie directly beneath 

 the sarcolemma. In the frog, and in many invertebrates, as the 

 beetles, they lie in the substance of the fibre, and, especially 

 in the latter class of animals, are surrounded by a mass of 

 granular protoplasm. Weber denies that in the adult frog 

 they are surrounded by this mass. 



Conclusions. From what precedes, it seems demonstrated 

 that striped muscular fibre consists of a transparent, semifluid 

 ground-substance, which is the contractile element. At certain 

 intervals a double layer of minute granules or spherules is 

 placed, which practically forms a transverse disk. The refrac- 

 tion of the light causes the substance bordering this disk to 

 appear brighter than the intermediate portion, which is only 

 occasionally seen in mammalian muscle as an indistinct and 

 usually a broken line, because the black stripes are so near to- 

 gether that the bright borders of two neighboring ones coalesce. 

 In invertebrates, as beetles, for instance, they are so far apart 

 that the dim stripe is proportionally broad, but it necessarily 

 disappears when by contraction the black stripes are brought 

 nearer together. Variations in the direction of the light, or 

 any obliquity of the disks, will cause peculiar effects, well- 

 nigh defying analysis. The writer's views coincide, in the main, 

 with Schafer's, except that he cannot accept the "handles" of 

 the latter's dumb-bell-shaped structures. As the writer has 

 stated in another paper, muscles in the leg of the Gyrinus 

 which have been exhausted by electricity show the stripes very 

 indistinctly, and contain a number of stray granules. Klein 

 has pointed out that if fresh muscular fibre of the frog is 

 teased out in salt solution, when a break of the substance oc- 

 curs inside the sarcolemma, " inside this tube a greater or less 

 number of granules are observed in active molecular move- 

 ment." These observations appear to confirm the views given 

 above. 



A good deal has been written about the effect of polarized 

 light on muscular fibre, and very different results have been 

 reached. Ranvier thinks it of no value in the discussion, be- 

 ' cause the same substance may be either doubly or singly re- 

 fracting, according to the pressure to which it is subjected. 

 This is certainly a strong argument against its value, espe- 



