68 ELEMENTS OF HISTOLOGY. [Chap. ix. 



a great number of fine, clear, longitudinal lines (see be- 

 low), and therefore under these conditions seem to be 

 made up of one row of granules. The membranes of 

 Krause appear fixed to the sarcolemma, so that while 

 a fibre contracts, or while it is contracted or shrunk, 

 owing to the action of hardening re-agents, or merely 

 in consequence of being detached from its fixations, its 

 surface is not smooth, but regularly and transversely 

 undulating, the valleys being caused by the attachment 

 of the membranes of Krause to the sarcolemma. 

 On stretching a fibre beyond its natural passive state, 

 the surface becomes also uneven and undulating, but 

 in a reverse manner from the above. 



85. These two membranous structures represent, 

 as it were, the framework. In the muscular com- 

 partments is contained the muscular substance, which 

 again consists of (a) the contractile or chief substance 

 (Rollett), which is a dim, broad, highly refractive, 

 doubly refractive disc, occupying the greater part of a 

 compartment, except a thinner or thicker layer at the 

 side of Krause's membrane. This layer is (b) a trans- 

 parent homogeneous fluid substance, forming the lateral 

 disc of Engelmann, or the secondary substance of 

 Rollett. It is isotropous. In this lateral disc occa- 

 sionally a transverse row of granules appears present, 

 but this is by no means of constant occurrence. The 

 contractile disc seems homogeneous, but is in reality 

 composed of prismatic or rod-shaped elements, the sar- 

 cous elements of Bowman, each being as long as the con- 

 tractile disc. They are very close, and there is left 

 between them in the fresh and living state an exceed- 

 ingly minute layer of a homogeneous transparent 

 interstitial substance, identical with that of the lateral 

 disc. After death and shrinking of the sarcous 

 elements, this interstitial substance is more marked, 

 and is then easily perceived as longitudinal clear 

 lines separating the sarcous elements in the iiidi- 



