294 



ELEMENTARY PHYSIOLOGY 



treatment, a thin superficial layer becomes sharply 

 separated from tlie deeper substance of tlie fibre as a 

 membrane of glassy transparency, the sarcolemma, 

 which ensheathes the striated and fil)rillated substance. 



The bright bands and the granular lines, on the other 

 hand, undergo little alteration. 



Under very higli powers each granular line looks like a 

 number of minute granules lying side 

 by side as an extremely thin plate, 

 the margins of which are attached to 

 the sarcolemma ; it is often spoken 

 of as Kratise's memhrnne. 



If the sarcolemma of a dead fibre be 

 torn with needles, the striated sub- 

 stance breaks up in different ways 

 according to the treatment to which 

 the fibi-e has been previously subjected. 

 It may break up into discs, each of 

 which contains a dim band. Or it 

 may break up into fibrils, each of 

 which pi'esents tlie same segmentaticm 

 as the whole fibre. These artificial 

 fibrils vary much in thickness accord- 

 ing to mode of preparation and the 

 skill of the operator ; they may some- 

 times be obtained of exceeding fine- 

 ness (Fig. 88, B). Transverse sections 

 of muscular fibre, which have been 

 frozen while perfectly fresh, present 

 minute close-set circular dots, which appear to repre- 

 sent the transverse sections of bundles of naturally existing 

 longitudinal fibrils. These dots are known as Cohn- 

 heim's areas. If the muscle substance is really in this 

 case unaltered the only possible interpretation of the fact 

 is that the fibre is really made up of fibrils, and that these 

 are invisible in the living muscle on account of their 

 having the same refractive power as. the interfibrillar sub- 



Fio. 89.— A Muscu- 

 lar Fibre (of Froo) 

 ENDING IN Tendon. 



Tlie striated muscu- 

 lar substance, m, has 

 shrunk from the sar- 

 colemma, s, the fi- 

 brils of the tendon, 

 t, being attached to 

 the latter. 



