COHNHEIM'S AREAS. 



289 



disks, which are formed by the lateral cohesion of the sarcous elements of adjacent 

 sarcostyles (fig. 329). To make up such a disk, therefore, every sarcostyle contributes 

 a particle, which coheres with its neighbours on each 

 side, and this with perfect regularity. 



From a consideration of these facts Bowman was led to 

 conclude the sub-division of a fibre into " fibrils " (sarcostyles) 

 "to be merely a phenomenon of the same kind as the separa- 

 tion into disks, only of more common occurrence, the cleavage 

 in the latter case taking place longitudinally instead of trans- 

 versely ; accordingly, he came to the conclusion that the 

 " fibrillaa " (sarcostyles) have no existence as such in the fibre, 

 any more than the disks ; but that both the one and the 

 other owe their origin to the regular arrangement of the 

 particles of the fibre (sarcous elements) longitudinally and 

 transversely, whereby, on the application of a severing force, 

 it cleaves in the one or in the other direction. That this con- 

 clusion was erroneous, however, is shown by the fact that a 

 fibre can be split into longitudinal elements after death even 

 without the action of any reagents, but never into disks ; 

 and also by the circumstance that in certain muscular fibres 

 (those which move the wings of many insects) a separation 

 into longitudinal elements (sarcostyles) can be seen to pre- 

 exist even in the living and contractile condition of the 

 fibre. Moreover, in these muscles, in consequence of the 

 large amount of interstitial substance between the sarcostyles, 

 the whole of a fibre never cleaves across into disks. 



Fig. 329. MUSCULAR FIBRE FROM 



THE LEO OF A BEETLE, TREATED 

 WITH DILUTE ACID, SHOWING A 

 TENDENCY TO BREAK ACROSS 

 INTO DISKS. (E. A. S. ) 



The sarcoplasm is in the form 

 of fine longitudinal lines with dot- 

 like enlargements. The ordinary 

 cross-stripes of the tissue are not 



If a transverse section of a muscular fibre, or the surface of a separated disk 

 (fig. 330 A), is examined with a high power, it appears to be marked out into small 

 polygonal areas separated by fine lines which, in acid preparations, have the 



Fig. 330. TRANSVERSE SECTIONS OF MUSCLE FIBRES. (E. A. S.) 



A. TRANSVERSE SECTION OF A MAMMALIAN MUSCULAR FIBRE SHOWING COHNHEIM'S AREAS. 

 Alcohol preparation. Three nuclei are visible under the sarcolemma. 



B. AN ISOLATED DISK OF LEG-MUSCLE OF A BEETLE TREATED WITH DILUTE ACID. 



The disk is seen partly on the flat, partly in profile, and exhibits the net-like appearance of the sarco- 

 plasm in the transverse section of the fibre : the meshes represent the areas of Cohnheim. 



C. TRANSVERSE SECTION OF MUSCULAR FIBRE OF LEG OF WASP, SHOWING A RADIAL DISPOSITION OF 



THE SARCOPLASM. ACID PREPARATION. 



appearance of a network (fig. 330, B). These areas represent sections of the 

 muscle-columns ; they are known as Cohnheim's areas, and the lines between them 

 represent the intercolumnar substance or sarcoplasm. The network is coarser near 

 the surfaces of such a disk, because, as will immediately be explained, the sarcoplasm 

 is increased in amount at regular intervals, corresponding with the bright striae ; by 

 alteration of the focus, however, a fine network can be made out through the whole 

 thickness of the disk. 



