CH. VI.] 



VOLUNTARY MUSCLE. 



If the surface is carefully focussed rows of apparent granules 

 are seen lying at the boundaries of the light streaks, and fine 

 longitudinal lines passing through the dark streaks may be 

 detected uniting the apparent granules (fig. 104). 



In specimens treated with dilute acids or gold chloride, the 

 granules are seen to be connected side by side, or transversely 

 also. This reticulum (fig. 105), with its longitudinal and transverse 

 meshes, was at one time considered to be the essential contractile 

 portion of the muscular fibre ; it was thought that on contraction 



Fig- >5- Portion of muscle-fibre of 

 water-beetle, showing network 

 very plainly. One of the transverse 

 networks is split off, and some of 

 the longitudinal bars are shown 

 broken off. (After Melland.) 



Fig. 106. Transverse section through 

 muscular fibres of human tongue. 

 The nuclei are deeply stained, 

 situated at the inside of the sar- 

 colemma. Each muscle fibre 

 shows " Cohnheim's areas." 

 X 450. (Klein and Noble Smith.) 



the transverse networks, with their enlargements, the granules, 

 became increased by the longitudinal strands diminishing in 

 length and running into them. Most histologists have rejected 

 this idea, and regard the network as mere interstitial substance 

 lying between the essentially contractile portions of the muscle. 

 A muscular fibre is thus made up of what are variously called 

 fibrils, muscle-columins or sarcostyles ; and the longitudinal inter- 

 stitial substance with cross networks comprising the reticulum just 

 referred to is called sarcoplasm. By the use of certain reagents, 

 such as osmic acid or alcohol, the muscle-columns or sarcostyles 

 may be completely separated from one another. 



A transverse section of a muscular fibre (fig. 106) shows the 

 sections of these sarcostyles ; the interstitial sarcoplasm is repre- 

 sented as white in the drawing. The angular fields separated 

 by sarcoplasm may still be called by their old name, areas of 

 Cohnheim. 



