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HANDBOOK OF PHYSIOLOGY. 



The sarcous substance stains with haematoxylin. A light interval may 

 bisect the sarcous substance if the fibre is stretched, which corresponds 

 with Hensen's disc. 



Appearances under Polarized Light. The appearances which 

 muscle presents when viewed under polarized light vary according as 

 the fibres are looked at, as fresh in their own plasma, or as hardened 

 fibres prepared and mounted in Canada balsam. 



The whole of the living fibre may be doubly refracting, the isotro- 

 pous part appearing as rows of dots separating transversely the princi- 

 pal material of the fibre. Shortly, according to Schiifer, it may be said 

 that the sarcoplasm is singly refracting, and that the sarcostyle is in 

 great part doubly refracting. In a fibre which is extended, after it has 

 been hardened in alcohol and mounted in Canada balsam, there are 



K - 



S.E. 



'S.E. 



Fig. 90. 



Fig. 91. 



Fig. 90. Sarcostyles from the wing-muscles of a wasp. A. A'. Sarcostyles showing- degrees of 

 retraction (? contraction). B. A sarcostyle extended with the sarcous elements separated into two 

 parts, c. Sarcostyles moderately extended (semidiagrammatic). (E. A. Schafer.) 



Fig. 91. Diagram of a sarcomere in a moderately extended condition, A, and in a contracted 

 condition, B. K, K, Krause's membranes; H, plane of Henson; S.E., poriferous sarcous element. 

 (E. A. Schafer.) 



alternate dark and light bands, the former corresponding to the light 

 intervals as seen in ordinary light, and the latter k> the various elements. 

 When the fibre is more contracted the dark line becomes narrower, and 

 the anisotropous intervals broader, but there is no interval of the bands 

 on contraction. It appears further that the chromatic portion only of 

 the Sarcostyles is anisotropous, and the sarcoplasm and the remainder of 

 the fibre is isotropous. 



(b.) Heart Muscle. The muscular fibres of the heart, unlike those 

 of most of the involuntary muscles, are striated; but although, in this 

 respect, they resemble the skeletal muscles, they have distinguishing 

 characteristics of their own. The fibres which lie side by side are united 

 at frequent intervals by short branches (fig. 92). The fibres are smaller 

 than those of the ordinary striated muscles, and their striation is less 

 marked. No sareolernma can be discerned, The muscle-corpuscles are 

 situate in the middle of the substance of the fibre; and in correspond- 



