STRUCTURE OF STRIATED MUSCLE. 545 



be looked at from the surface, lighter and darker bands of a 

 certain breadth are as a rule seen alternating with one 

 another. These bands or zones, he thought, are caused by the 

 regular juxtaposition of thicker and thinner segments of the 

 fibrils. The muscular fibre was thus, as Valentin stated, a 

 fasciculus of fibrils, and since then it has also been termed a 

 primitive muscular fasciculus (Muskel-primitiv-biindel). 



Bowman maintained that the fibrils are not originally 

 present in the fibre, but that they are the product of a process 

 of disintegration. In some instances, he says, the fibres do not 

 split in the longitudinal, but in the transverse direction, in 

 consequence of which disks are formed . If a muscular fibre 

 undergo division in both directions, that is to say, if the 

 whole length were divided into fibrils, and the whole thickness 

 into disks, minute particles, the " sarcous elements," would be 

 obtained, of which the muscle is properly composed. Rollett 

 objected to this view, that Bowman only described one kind 

 of material, and had overlooked the connecting substance. 



Wharton Jones was the first to mention the alternate 

 succession of two different substances in the longitudinal 

 direction of the fibre ; namely, the disks and an intermediate 

 substance. 



Dobie maintained that the fibrils themselves consisted of 

 two different substances, and described them as composed of a 

 linear series of alternating bright and dark bodies. Rollett 

 assented to this view. He regarded the muscle-substance 

 of the fibre as composed, in Schwann's sense, of a fascicu- 

 lus of fibrils, each fibril being segmented by an alternation of 

 two kinds of substances, to one of which, on account of its 

 harder contours, he ascribed a greater refractive power than 

 to the other. The stronger refracting substance he termed the 

 chief substance (Haupt-substanz), the other the intermediate 

 substance (Zwischen-substanz). Taking the fibre as a whole, 

 disks of chief and intermediate substance alternate with each 

 other, the latter corresponding to Bowman's disks. Looking at 

 the fibrils alone, the chief substance corresponded to a sarcous 

 element or a sarcous particle. Rollett might at that time 

 already have been acquainted with Briicke's discovery, to the 

 effect that the doubly refractile property was possessed by the 

 VOL. III. N N 



