QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 417 



grey band seems to disappear in an early stage of contraction, 

 but this is not easy to make out. There seems to be no law 

 regulating the wave of contraction, which may run towards or 

 away from the tendon. Dwight has never seen the fibre 

 assume a homogeneous appearance during contraction, as 

 stated by Merkel, nor during repose, as Schiifer thinks. Lon- 

 gitudinal striation was only seen in unhealthy fibres. It is 

 superficial, and probably only in the sarcolemma. Dwight 

 concludes that '' the fibre consists of a sheath, the sarcolemma, 

 and of a ground substance, in Avhich elements which may be 

 provisionally called granules are embedded in transverse 

 double rows. There is no reason to suppose that the differ- 

 ence between tlie white and the grey has any other than an 

 optical cause, namely, that the part of the ground substance 

 nearest the black bands receives, not only the rays of light 

 that would naturally strike it, but others reflected or refracted, 

 or both, from the black bands, and which do not strike the 

 middle of the space between the latter (Heppner, Schafer). 

 If this be admitted, it is merely a corollary that in con- 

 traction the grey should disappear, as is the case. No 

 appearances have been seen that are suggestive of the 

 bundles of Schafer's dumb-bell-like rods, which, indeed 

 (judging from the abstract of his paper), he has assumed 

 rather than demonstrated. As has been already stated, 

 nothing like fibrillar structure is to be seen in the living and 

 healthy fibre. 



The sarcolemma is firmly attached to each edge of the ends 

 of the black bands, and the granules must, in some Avay, be 

 prevented from spreading laterally, so as to give support for 

 the folds into which the muscle contracts. The ground 

 substance is the contractile element ; it is also highly elastic. 

 When the fibre is stretched all parts become narrower, and 

 when contracted broader, but in the latter case the change 

 is chiefly in the ground substance. 



2. Sonie Points relating to the Histology and Physiology 

 of Striped Muscles. — Ranvier {' Arch, de Physiol.,' Jan., 

 1874) has examined the action and structure of the two kinds 

 of striped muscles (excluding the heart) that are found in 

 some animals. These are pale and dark red muscles. Thus, 

 in the rabbit the semitendinosus, crureus, quadratus femoris, 

 and soleus, are red ; while the internal vastus, triceps femoris, 

 adductor magnus, biceps, &c., are pale muscles. The same 

 distinction is found in fishes, and in skates and torpedoes 

 there are muscles formed of the two kinds of fibres. The 

 dark colour of the red muscle does not depend on its contain- 

 ing more blood, as when all the blood has been washed out 



