288 



MANUAL OF HISTOLOGY. 



a darker and clearer portion (fig. 277, 5, c, d) (3) ; it showed further, that 

 the clear part underwent solution by degrees, while the dark zone remain- 

 in^ over occasionally presented to view the sarcous elements of a disk, as 

 though in the act of separation from one another. 



The improved and greatly increased magnifying power of our new 

 microscopes has since rendered it no longer difficult to obtain a view 

 of the fleshy prisms and of the fibrous structure of many muscles (fig. 

 278). The lamprey, and, better still, the lower amphibia (Proteus, Siredon), 

 afford very good objects, owing to the large size' of their sarcous elements. 

 However, the same may be recognised in the smaller particles of the 

 muscles of frogs, mammals, and human beings (4). 



The prisms appear now as cylindrical or hexagonal prismatic particles, 

 of greater height than breadth. Their length in the proteus (fig. 278, 1, a) 

 is 0.0017 mm., in the frog (fig. 280) 0-0013 mm., in the pig (fig. 278, 2, a) 

 and in man O'OOl 1-0*0012 mm. Standing one beside the other, they 

 form the dark transverse zones, and are almost in actual contact with one 

 another as a rufe, owing to the scanty amount of interposed cement 

 (fig. 278, 2, a; fig. 279, a). 



Those spots are particularly instructive where the sarcous elements of a 



Fig. 1. 



Fig 2. 



Fig. 278. Two muscle fibres from the proteus, 

 1, and fig. 2, magnified 1000 times. (The first 

 was an alcohol preparation, the latter treated 

 with acetic acid of 1-01 per cent.), a, sarcous 

 elements; 6, clear longitudinal cement. At a, 

 the sarcous elements are more separated from 

 one another, and the transverse cement is visible, 

 c, nucleus. 



Fig. 279. Kravse's transverse 

 disks, a, a. 1, a muscle fibre 

 without, 2, one under strong ex- 

 tension; both highly magni- 

 fied (Martyri); 3, a fibre from 

 the dog immediately after 

 death. 



transverse row appear somewhat distant from one another (fig. 278, 1 

 below, 2, a*). 



In our description so far of the structure of the muscle fibre, we have 

 intentionally followed up the historic course of the opinions held regarding 

 it, in order to facilitate the comprehension of the most recent investiga- 

 tions by the reader. 



From the newest researches we learn that our earlier views were incom- 

 plete. But still the field of inquiry is so exceedingly wide, the matters 

 to be dealt with lie so near the verge of invisibleness, and the composition 

 of the fleshy mass is so very unstable, that the views of present-day 

 observers differ widely. 



In the first place, the transparent transverse zone is traversed by a very 

 fine dark line. This was referred to by the English observer " Martyn 

 with others, and the second edition of this hand-book, in the year 1862. 



