292 MUSCULAR TISSUE. 



them, and they can then be studied independently of that substance. And in the 

 first place it may be mentioned that they can, under these circumstances, be seen 

 to contract, whereas the sarcoplasm gives no sign of contractility : they therefore 



Fig. 334. TRANSVERSE SECTION OP PART OF A WING-FIBRK OP AN 



INSECT SHOWING THE SARCOSTYLES SURROUNDED BY SARCOPLASM. 

 (E. A. S.) ^ 



The muscle was treated with chloride of gold and acid, so that 

 the sarcoplasm has become stained, the sarcostyles being left 

 colourless. 



form the active portion of the fibre. The intimate 

 structure of the sarcostyles can be advantageously 

 investigated in such isolated elements, and this both 

 in the living condition and under the influence of re- 

 agents. In the living condition they show, as in the 

 ordinary muscles, alternations of bright and dim striae. 

 Each bright stria is bisected by a line which is the optical section of a transverse 

 membrane (membrane of Krause). These membranes thus divide the fibre into a 

 series of segments, which may be termed sarcomeres. In alcohol-hardened muscle each 

 sarcomere can be seen to contain (1) in the middle a strongly refracting disk-like 

 sarcous element ; (2) at either end (next the membrane of Krause) a clear interval 

 occupied by hyaline substance. With high powers the sarcous element may be 

 made out to be composed of a sarcous substance, which stains with hsematoxylin, 

 and is pierced by short tubular canals which extend from the clear interval as far as 

 the middle of the disk ; these canals give it a longitudinally striated appearance. 

 Fine longitudinal strias which appear to be due to delicate extensions of the sarcous 



Fig. 335. DISK-LIKE SARCOUS ELEMENT OP WING-MUSCLE SHOWING ITS TUBULAR- 

 STRUCTURE. HIGHLY MAGNIFIED. (E. A. S.) From a photograph. -* 



A, Profile view. B, Viewed in optical transverse section. 



substance (perhaps delicate septa), may also, under favourable 

 circumstances be seen traversing the clear intervals. If the 

 sarcostyle is extended, the sarcous elements tend to separate into two parts, with 

 an interval between them (fig. 333, B) ; this median clear interval corresponds 

 with the line of Hensen (p. 288). 1 Conversely, if the muscle is retracted (or 

 contracted) the sarcous elements tend to encroach on the clear intervals and 

 approach the membranes of Krause ; and at the same time they become swollen, 

 so that the sarcomeres are bulged out at their middle and contracted at their 

 ends. The sarcostyles thus become moniliform, and in fresh and unstained fibres 

 the effect of this form upon the light transmitted through the muscle is such that 

 the swollen part looks comparatively clear, while the constricted part has a dark 

 appearance ; and since this constricted part corresponds with the bright stria of the 

 extended muscle, the striae appear to have become reversed during contraction. In 

 a stained fibre, however, it is easy to see that no such reversal takes place in 

 contraction (fig. 333, A, A'). 



Comparison of the structure of muscle -with that of amoeboid protoplasm. If we 

 compare the structure of the muscle-columns as shown in the wing-muscles with that of 

 amoeboid protoplasm, we find many points of coincidence. Both are composed of two kinds of 

 substance, viz., a porous substance or spongioplasm which stains with hasmatoxylin and similar 

 reagents, and a clear matter or hyaloplasm which remains unstained. In both cases the 

 process of contraction is accompanied by a flowing of the hyaloplasm into the pores or meshes 



1 With still further extension, each sarcous element may separate into four parts, in which case the 

 two parts nearest the transverse membrane have been termed the accessory disks. 



