OPTICAL PHENOMENA OF MUSCULAR CONTRACTION 743 



can actually be split up into discs by certain reagents. It also shows 

 a longitudinal striation, and can be separated into fibrils. Some have 

 supposed that the discs are the real structural units which, piled end 

 to end, make up the fibre. The fibrils they consider artificial. This 

 view is erroneous. It seems certain that the fibres are built up from 

 fibrils ranged side by side, and that the discs are artificial. The con- 

 tents of the muscle-fibre appear to consist of two functionally different 

 substances, a contractile substance, and an interstitial, perhaps nutri- 

 tive, non-contractile material of more fluid nature. The contractile 

 substance is arranged as longitudinal fibrils embedded in interfibrillar 

 matter (sarcoplasm). In a muscle impregnated with chloride of gold 

 the interfibrillar matter appears as a network. 



Schafer has described the contractile elements of the muscle-fibre 

 (Figs. 248, 249) as fine columns (sarcostyles), divided into segments 



(sarcomeres) by thin transverse 

 discs (Krause's membranes), occu- 

 pying the position of the middle of 

 each light stripe. Each sarcomere 

 contains a sarcous element la. por- , 

 tion of the dark stripe) with a clear 

 substance at its ends, filling up the 



Fig. 248. Living Muscle of Water- 

 Beetle (highly magnified) (Schafer). 

 s, sarcolemma ; a, dim stripe ; 

 b, bright stripe; c, row of dots in 

 bright stripe, which appear to be 

 the enlarged ends of rod-shaped 

 particles, d, but in reality represent 

 expansions of the interstitial sub- 

 stance (sarcoplasm). 



Fig. 249. Portion of Leg 

 Muscle of Insect, treated 

 with Dilute Acetic Acid 

 (Schafer). S, sarco- 

 lemma; D, dot -like en- 

 largement of sarcoplasm; 

 K, Krause's membrane. 

 The sarcous elements 

 have been swollen and 

 dissolved by the acid. 



space between the sarcous element and Krause's membrane, and con- 

 stituting a portion of the light stripe. The sarcous element is itself 

 double, and if the fibre be stretched, the two portions separate at a 

 line which runs transversely across the middle of the dim stripe (Hensen's 

 line). Schafer considers that the appearance of longitudinal fibrillation 

 in the sarcous elements is due to the presence in them of fine longi- 

 tudinal canals or pores. 



The Krause's membrane of the individual fibrils is scarcely ever 

 visible in an intact mammalian fibre, and the apparent line in the clear 

 stripe of an intact fibre is an optical appearance due to interference of 

 light. Kuhne, who was fortunate enough to find one day a small 

 nematode worm moving in the interior of a fibre, saw it pass along 

 the fibre with perfect freedom, ignoring Krause's membrane. Possibly, 

 however, it was moving in the sarcoplasm, the fibrils being simply 

 pushed aside. 



