98 NORMAL HISTOLOGY, 



and most warm-blooded animals lie scattered upon 

 the surface of the contractile substance ; 3, the 

 sarcolemmfr, a thin homogeneous sheath or tube, 

 which tightly encloses the other elements. 



i. If we examine a fresh muscle-fibre, or one 

 which has been hardened under favorable condi- 

 tions, with moderately high powers, we see that the 

 contractile substance is indistinctly longitudinally 

 striated ; and if we treat muscle with certain chem- 

 ical agents, such as chromic acids or its salts, we 

 find that by slightly teasing, the fibres break up 

 along the longitudinal striae into a multitude of fine 

 fibrillse, which are called primitive muscle-fibrillce. 

 Again, if we examine the fresh and hardened fibres 

 still further, we find that in addition to the longi- 

 tudinal striations, they are crossed by more promi- 

 nent, narrow, alternating, dark and light bands or 

 stripes, the relative width of the stripes varying ac- 

 cording as the muscle is seen in a state of contrac- 

 tion or relaxation. Still further, if we soak a fresh 

 muscle for twenty-four hours in a half-per-cent. 

 solution of hydrochloric acid, and then tease it, we 

 find that the fibres, instead of breaking up longi- 

 tudinally into fibrillae, break across transversely into 

 thin discs. We thus see that, by breaking up in 

 these two directions, we may conceive of the fibre 

 as being resolvable into a multitude of tiny pris- 

 matic structures, which are called sarcous elements. 

 The central portion of each prism or sarcous ele- 



