14 PHYSIOLOGY OF MUSCLES AND NERVES. 



darker streaks, placed at right angles to the longitudinal 

 direction of the fibres. For this reason, these muscle- 

 fibres are called streaked or striated muscles, in order 

 to distinguish them from certain others of which we 

 shall presently learn. In order to obtain an approxi- 

 mate idea of the appearance of one of these fibres, we 

 may imagine it as a roll of coins, the separate pieces of 

 which are, however, transparent and alternately lighter 

 and darker. Some observers have indeed assumed that 

 a muscle-fibre really consists of discs of this sort, ranged 

 side by side. The fibres, when treated with certain 

 chemical re-agents, separate into these discs, and while 

 some of them yet remain attached to each other, the 

 fibre very closely resembles a roll of coins the pieces of 

 which are falling away from each other. But there are 

 other re-ag^nts which split up the fibre in a longitudinal 

 direction, so that it separates into extremely delicate 

 smaller ^6?'es or fibrillce each of which still exhibits the 

 alternation of lighter and darker parts, which, in the 

 entire fibre, produce the transverse striation. More- 

 over it can be shown that a muscle-fibre when recently 

 taken from the living animal must, in reality, be of a 

 fluid, or, at least, of a semi-fluid nature. So that it is 

 impossible to affirm that either the discoid or the fibril- 

 loid structure actually exist in the muscle-fibre itself; 

 it must rather be assumed that both forms of structure 

 are really the result of the application of re-agents 

 which solidify the originally fluid mass and split it up 

 in a longitudinal or transverse direction. 



2. It is hard to say what the true character of the 

 fresh, or, as we may also call it, the living muscle-fibre 

 really is. Eecent observations by means of very much 

 improved and very highly-magnifying microscopes, have 



