MUSCULAR TISSUE. 185 



and the rounded areae of the transverse section are 

 simply the optical expressions of the boundaries of these 

 fibrils. In the perfectly unaltered state of the tissue, 

 however, the fibrils are so closely packed that their 

 boundaries are scarcely discernible. 



Thus each muscular fibre may be regarded as com- 

 posed of larger and smaller bundles of fibrils im- 

 bedded in a nucleated protoplasmic framework which 

 ensheaths the whole and is itself invested by the sar- 

 coleinma. 



As the fibre dies, the nuclei acquire hard, dark contours 

 and their contents become granular, while at the same 

 time the fibrils acquire sharp and well-defined boundaries. 

 In fact, the fibre may now be readily teased out with 

 needles, and the fibrils isolated. 



In muscle which has been treated with various reagents, 

 such as alcohol, nitric acid, or solution of common salt, 

 the fibrils themselves may be split up into filaments of 

 extreme tenuity, each of which appears to answer to 

 one of the granules of the septal lines. Such an 

 isolated muscle filament looks like a very fine thread 

 carrying minute beads at regular intervals. 



The septal lines resist most reagents, and remain 

 visible in muscular fibres which have been subjected to 

 various modes of treatment ; but they may have the 

 appearance of continuous bars, or be more or less com- 

 pletely resolved into separate granules, according to cir- 

 cumstances. On the other hand, what is to be seen in 



