1873.] 



Structure of Striped Muscular Fibre. 



243 



the axis of the fibre) and of a vast number of minute rod-like particles, 

 to which he applies the term muscle-rods, which are closely arranged 

 side by side and parallel to the axis of the fibre, so as to form by their 

 juxtaposition as many series as there are disks of dim substance in the 

 fibre. The main part or shaft of each muscle-rod is imbedded in and 

 traverses a disk of dim substance, while the ends, which are enlarged at 

 the extremity into little knobs or heads, extend into the bright disks. 

 These little knobs it is which give the appearance of the line of dots 

 which has long been described as existing in the middle of each bright 

 stripe ; when the fibre is somewhat extended this line appears double, 

 owing to the separation of the heads of the two successive series of 

 muscle-rods which meet in the middle of the disk of bright substance. 

 The author describes the rods as differing somewhat both in relative 

 position and in form, these differences being accompanied by corre- 

 sponding changes in the appearance of the ground-substance. The 

 principal changes are those of form. Thus, in what the author is 

 inclined to regard as the state of absolute rest, the rods are uniformly 

 cylindrical without terminal enlargements ; in this case only a longi- 

 tudinal fibrillation is to be seen in the fibre, all trace of transverse 

 striping having disappeared. In the normal state of slight tension, 

 however, the rod-heads make their appearance, and with them the bright 

 substance by which they are surrounded, so that the dim ground- 

 substance now presents a transversely striated aspect. In contraction 

 of the muscle the heads of the rods become enlarged at the expense of 

 the shaft, the extremities of each muscle-rod thus approaching one 

 another : the enlarged heads, being closely applied both to the neigh- 

 bouring ones of the same series and to those of the next series which 

 meet them in the bright stripe, the line of dots now appears as a dark 

 transverse band with bright borders. As the contraction proceeds, and 

 these dark bands approach one another, the bright borders encroach upon 

 the dim stripe, which finally disappears, so that its place is taken up by 

 a single transverse bright stripe. Consequently contracted muscle shows 

 alternate dark and light stripes ; the former, however, are in this case due 

 to the enlarged juxtaposed extremities of the rods, the light on the other 

 hand being mainly composed of the ground-substance which has become 

 accumulated in the intervals between their shafts. 



After giving a description of the appearances observed in transverse 

 section, when examined in the normal state without addition, and after 

 the consideration of those which are met with in sections from frozen 

 muscle examined in \ per cent, solution of common salt, and which have been 

 described by Cohnheim, the author proceeds to consider the nature of 

 the ground-substance, and more especially the transversely striated 

 appearance which it ordinarily presents. He gives it as his opinion that 

 the ground-substance is in reality uniform in nature throughout, and 

 that the bright bands which cross it are due to an optical effect produced 



