92 PRACTICAL HISTOLOGY. 



Each striped fibre of the voluntary muscles is an elon- 

 gated spindle developed from a cell. The sarcolemma may 

 be regarded as the cell membrane ; the nuclei inside the 

 sarcolemma are proliferations from the original nucleus, and 

 the sarcous substance is a modification of the original pro- 

 toplasm. 



140. The Sarcous Substance (H.) To soften the 

 connective tissue between the fibres, and permit of their 

 ready dissociation with needles, prepare muscle as follows. 

 Take a narrow strip of the sartorius of a rabbit just killed ; 

 tie a thread round both ends ; fix the threads to a piece of 

 wood with the muscle gently stretched ; then place in dilute 

 alcohol ( 284) for two days or so. Tease a small piece 

 with needles in Farrants' solution; cover, examine, and pre- 

 serve. 



Each fibre is seen to be crossed by alternate light and 

 dim stripes. By altering the focus it may be seen that the 

 stripes are not superficial, but extend through the whole 

 thickness of the fibre. 



141. Cleavage of the Sarcous Substance (H.) a. 

 With a razor make a thin V. S. of striped muscle of cat or 

 rabbit hardened in \ per cent chromic acid ( n) to 

 facilitate the cleavage of the sarcous substance. Tease 

 with needles in a drop of Farrants' solution; cover, and 

 examine. 



The fibre cleaves most readily in a longitudinal direc- 

 tion. The result of such cleavage is a bundle of fibrils^ 

 each marked with a light and dim transverse stripe like the 

 original fibre. A very fine dark line may with a power 

 of about 1000 be seen crossing the light stripe trans- 

 versely, and dividing it into two equal portions. If the 

 fibre or fibrils cleave transversely, the rupture takes place 

 through this faint dark line in the clear stripe. 



b. Remove the slide from under the lens, and forcibly 

 press down the cover-glass with the handle of a knife or 

 needle, and examine again. The pressure often causes the 

 fibres and fibrils to cleave transversely. When a fibre 

 cleaves transversely, it gives rise to a number of discs. 

 The transverse cleavage of a fibril produces a number of 



