PROGEESS OF MICKOSCOPICAL SCIENCE. 37 



of the disk of bright substance. The author describes the rods as 

 differing somewhat both in relative position and in form, these differ' 

 ences being accompanied by corresponding changes in the apjjearanco 

 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 longitudinal 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 neighboiu'ing 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 apj)roach one another, the 

 bright borders encroach upon the dim stripe, which finally disappears, 

 so that its j)lace is taken up by a single transverse bright strijje. 

 Consequently contracted muscle shows alternate dark and bright 

 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 accumu- 

 lated 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 gi-ound- 

 substance, and more especially the transversely striated aj)pearance 

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

 ground-substance is in reality uniform in nature thi'oughout, and that 

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

 by the presence of the globular heads of the muscle-rods, which have 

 a different refractive index from that of the ground-substance. That 

 such an explanation is possible, is shown by tlie examination of minute 

 oil-globules imbedded in gelatine, which appear under the microscope 

 as dark sj)ots with a bright surrounding, the juxtaposition of several 

 such dots giving the effect of a bright band. That the bright trans- 

 verse bands in muscle are similarly produced by the juxtaposition of 

 the rod-heads would appear fi'om the following amongst other con- 

 siderations : — 



1. "Where the rod-heads are smaller the bright bands are corre- 

 spondingly narrower. 



2. Where the rod-heads have become merged into the shafts, so as 

 no longer to be seen as distinct objects, the bright transverse stripes 

 have also entii'ely disappeared. 



3. When in contraction the rod-heads enlarge and encroach on the 

 shaft, their bright borders accompany them and encroach on the dim 



