in 



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lai 



THE MUSCLES. 533 



styles are united into the muscle-fibers. It is the protoplasm of the 

 muscle-corpuscles,, and forms a fine network throughout the whole 

 muscular fiber. 



From an examination of the aforementioned facts, Bowman was 

 induced to believe that the division of the fiber into fibrils, or sarco- 

 stj'les, was merely a phenomenon of the same kind as the separation 

 into discs, only a more common occurrence. 



COHNHEIM'S AREAS. If a transverse section be made of a mus- 

 cular fiber, or the surface of a separated disc be examined with a 

 strong objective, there appear in the field small polygonal areas 

 separated by fine lines. In acid preparations they give the appear- 

 ance of a network. These areas represent sections of the muscle- 

 columns, and are usually designated as Cohnheimfs areas. The line 

 between them represents the sarcoplasm, or intercolumnar' substance. 



When a muscle-fiber placed in fresh serum is examined, fine, 

 longitudinal lines are seen running through the cross-striping. If, 

 now, a weak acid is added to swell the muscular substance and render 

 it more transparent, these lines can be traced from end to end of the 

 fiber. By careful management of the microscope, it is found that 

 these lines are really the optical section of the planes of separation 

 between the sarcostyles ; that is to say, the optical effect of the sarco- 

 plasm, or intercolumnar substance. The sarcop'asm, in transverse 

 section, presents the aspect of network; in longitudinal optical sec- 

 tion it has the appearance of fine, parallel lines. The student can 

 very readily imagine how these effects can be produced by the pres- 

 ence of a small amount of interstitial substance lying between closely 

 packed prismatic columns. 



In most muscular fibers the sarcoplasm exhibits a peculiarity of 

 arrangement which has a very characteristic influence upon the op- 

 tical appearance of the fiber. In a longitudinal view of fresh muscle, 

 e lines representing intercolumnar sarcoplasm present at regular 

 .tervals along their course rather marked enlargements. These en- 

 ements lie in the bright cross-strise, either H their middle or near 

 eir junction with the dim cross-stripes. These sarcoplasm- nodules 

 e the appearance of dots upon fine longitudinal lines which run 



ugh the muscle; in the more extended fibers these dots are in 

 j rows. In less extended parts they are thicker and blend 

 er in the middle of the bright stride. 



Structure of the Wing-muscles of Insects. The study of these 

 cles has furnished the key to the comprehension of the intimate 



