STRUCTURE OF VOLUNTARY MUSCLE. 



[BOOK i. 



studded with fine dots ; but if the muscle were first frozen before the 

 section was made, it would be seen to be divided by fine lines into a 

 number of angular areas, known as Cohnheirris areas; as if the whole 



FIG. 54. DIAGRAM ILLUSTRATING THE STRUCTURE OF A STRIPED MUSCULAR FIBRE. 



(After Engelmann.) 



The specimen was taken from the abdominal muscles of Telephorus melanurus, and 

 made rigid by being plunged into 50 p.c. alcohol: a represents the fibre in various stages 

 of contraction, when viewed in common light; 6 is a schema of the same fibre in polarized 

 light. 



1, 2, represent the broad dim bands in the fully relaxed condition ; in, Hensen's 

 disc (Mittelscheibe) ; q, darker portion of broad dim band (Querscheibe) ; z, Krause's 

 membrane, appearing double (Zwischenscheibe) ; n, accessory band (Nebenscheibe) ; 

 i, i, intermediate substance, forming the broad bright stripe or band. 



Of the various segments, 1 and 2 are fully relaxed ; 3, 4 and 5 are in the beginning 

 of contraction ; 6, 7 and 8 constitute the homogeneous stage of contraction ; and from 9 

 onwards the segments are in the stage of transposed bands, the original bright stripe 

 being now dimmer than the original dark stripe. 



6 shews that there is no transposition of doubly refracting and singly refracting 

 substance on contraction. 



For the sake of simplifying the diagram the double refraction of Krause's membrane 

 and the accessory bands is not indicated. 



fibre consisted of a number of compressed columns or prisms sur- 

 rounded by the sheath of the sarcolemma. Were we to irrigate these 

 fresh specimens of muscular tissue with dilute acetic acid, the muscle 

 would swell up, and the transverse striation would become faint, 

 while here and there a third element of the tissue, viz. the nuclei, 



