MUSCLE 



639 



containing a substance readily stained by various dyes ; (2) an 

 ' intermediate segment ' of cylindrical shape, the general substance 

 of which does not readily stain. The intermediate segment con- 

 tains in its centre a globule (Dobie's globule), which is easily stained.* 

 The fibrils are regularly arranged in bundles within the fibre. The 

 apposition of Bowman's elements gives rise to the dim stripe ; the 

 apposition of the intermediate segments to the clear stripe ; the appo- 

 sition of the Dobie's globules to a line in the middle of the clear stripe 

 (Dobie's line) . Dobie's line has by some been considered to represent 

 a membrane made up of the apposed Krause's membranes of all 

 the fibrils. But the Krause's membrane of the individual fibrils is 



scarcely ever visible in an intact 

 mammalian fibre (Schafer), 

 and the apparent line in the 

 clear stripe of an intact fibre 

 is an optical appearance due 

 to interference of the light. 

 Kiihne, who was fortunate 



FIG. 224. LIVING MUSCLE OF 

 WATER-BEETLE (HIGHLY MAGNI- 

 FIED) (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 substance 

 (sarcoplasm). 



FIG. 225. PORTION OF 

 LEG MUSCLE OF INSECT, 

 TREATED WITH DlLUTE 

 ACETIC ACID (SCHAFER). 



S, sarcolemma ; D, dot- 

 like enlargement of sarco- 

 plasm ; K, Krause's mem- 

 brane. The sarcous ele- 

 ments have been swollen 

 and dissolved by the acid. 



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. 



Changes during Contraction. When a muscle contracts, according 

 to Schafer, the clear substance between the Krause's membrane and 

 the sarcous element passes into the canals, which are open towards 

 Krause's membrane, but closed towards Hensen's line. The sarcous 

 element therefore swells up, and the sarcomere is shortened. In the 

 extended muscle the clear substance leaves the pores of the sarcous 

 element, and accumulates in the space between it and Krause's 



* In the muscles of certain invertebrate animals, though not in those 

 of vertebrates, the intermediate segment contains, in addition to Dobie's 

 globule, two pear-shaped bodies (Flogel's elements), each of which occupies 

 an intermediate position between Dobie's globule and the end of the 

 adjoining Bowman's element. Flogel's elements also stain well, and are 

 doubly refracting. 



