MUSCULAR TISSUE. 183 



This mucli is readily seen in a specimen of muscular 

 fibre taken from any part of the body, and whether alive 

 or dead. But the results of the ultiuiate optical analysis 

 of these appearances, and the conclusions respecting the 

 normal structure of striped muscle which may be legiti- 

 mately drawn from them, have been the subjects of much 

 controversy. 



Quiescent muscular fibres from the chela of the forceps 

 of a crayfish, examined while still living, without the 

 addition of any extraneous fluid, and with magnifying 

 powers of not less than seven or eight hundred diameters, 

 exhibit, the following appearance. At intervals of about 

 l-4000th of an inch, very delicate but dark and well- 

 defined transverse lines are visible ; and these, on careful 

 focussing, appear beaded, as if they were made of a series 

 of close-set minute granules not more than 1 -20,000th 

 to 1 -30,000th of an inch in diameter. These may be 

 termed tlie septal lines (fig. 52, D and E, a; C, 1—5; 

 fig. 53, s). On each side of every septal line there 

 is a very narrow perfectly transparent band, which may 

 be distinguished as the septal zone (fig. 53, sz). Upon 

 this follows a relatively broad band of a substance which 

 has a semi-transparent aspect, like very finely ground 

 glass, and hence appears somewhat dark relatively to the 

 septal zone. Upon this inter-septal zone (is) follows 

 another septal zone, then a septal line, another septal 

 zone, an inter-septal zone, and so on throughout the 

 whole length of the fibre. 



