556 A MANUAL OF PHYSIOLOGY 



exists, it must either be incomplete, or much more easily ruptured 

 than the sarcolemma ; for Kiihne, 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. Each sarcomere, according to Schafer, contains a 

 sarcous element (a portion of the dark stripe) with a clear substance 

 at its ends, filling up the space between the sarcous element and 

 Krause's membrane, and constituting 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). The small polygonal areas 

 seen in a cross-section of a fibre (Cohnheim's areas) represent the 

 cross-sections of the sarcostyles separated from each other by sarco- 

 plasm. Schafer's muscle-columns or sarcostyles are units of greater 

 transverse diameter than the fibrils of Kolliker, Rutherford, etc., and 

 he considers that the appearance of longitudinal fibrillation in the 

 sarcous elements is due to the presence in them of fine longitudinal 

 canals or pores. 



Rutherford has given a somewhat different account of the matter. 

 According to him, each fibril is made up of a longitudinal row of 

 segments of two kinds alternating with each other (Fig. 165): 

 (i) 'Bowman's elements,' shaped like an elongated hour glass, and 

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

 1 intermediate segment ' of cylindrical shape, the general substance 

 of which does not readily stain. The intermediate segments 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 

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

 stripe (Dobie's line). 



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 there- 

 fore 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 membrane. The sarcomere is thus lengthened 

 and narrowed. While the existence of Schafer's pores is not 



* 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. 



