CIT. VI.] SARCOUS ELEMENTS 83 



columns, but under the influence of some reagents like dilute hydro- 

 chloric acid, it can be broken up into discs, the cleavage occurring in 

 the centre of each light stripe. Bowman, the earliest to study 

 muscular fibres with profitable results, concluded that the subdivision 

 of a fibre into fibrils was a phenomenon of the same kind as the cross 

 cleavage into discs. He considered that both were artificially pro- 

 duced by a separation in one qr the other direction of particles of the 

 fibre he called "sarcous elements." The cleavage into discs is how- 

 ever much rarer than the separation into fibrils; indeed, indications 

 of the fibrils are seen in perfectly fresh muscle before any reagent 

 has been added, and this is markedly evident in the wing muscles of 

 many insects. It is now believed that a muscular fibre is built up 

 of contiguous fibrils or sarcostyles, while cleavage into discs is a 

 purely artificial phenomenon. 



Haycraft, who has also investigated the question of muscular 

 structure, concludes that the cross striation is entirely due to optical 

 phenomena. The sarcostyles are varicose, and where they are en- 

 larged different refractive effects will be produced from those caused 

 by the intermediate narrow portions. This view he has very in- 

 geniously supported by taking negative casts of muscular fibres by 

 pressing them on to the surface of collodion films. The collodion 

 cast shows alternate dark and light bands like the muscular fibres. 



Schafer is unable to accept this view; he regards the substance of 

 the sarcostyle in its dark stripes as being of different composition, 

 and not merely of different diameter, from the sarcostyle in the region 

 of the light stripes ; it certainly stains very differently with many 

 reagents, especially chloride of gold. His views regarding the inti- 

 mate structure of a sarcostyle have been worked out chiefly in the 

 wing muscles of insects, where the sarcostyles are separated by a 

 considerable quantity of interstitial sarcoplasm, and a brief summary 

 of his conclusions is as follows : 



Each sarcostyle is subdivided in the middle of each light stripe by 

 transverse lines (membranes of Krause) into successive portions, 

 which may be termed sarcomeres. Each sarcomere is occupied by a 

 portion of the dark stripe of the whole fibre; this portion of the 

 dark stripe may be called a sarcous element.* The sarcous element 

 is really double, and in the stretched fibre (fig. 108, B) separates into 

 two at the line of Hensen. At either end of the sarcous element is 

 a clear interval separating it from Krause's membrane; this clear 

 interval is more evident in the extended sarcomere (fig. 108, B), but 

 diminishes on contraction (fig. 108, A). The cause of this is to be found 

 in the structure of the sarcous element. It is pervaded with longi- 

 tudinal canals or pores open towards Krause's membrane, but closed 



* Notice that this expression has a different meaning from what it originally 

 had when used by Bowman. 



