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-agents which split up the fibre in a longitudinal 

 direction, so that it separates into extremely delicate 

 smaller fibres or fibrilloK 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- 

 It >id structure actually exist in the muscle-fibre itself; 

 it must ratln-r be assumed that both forms of structure 

 ;nv 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 \\c may also call it, the living muscle-fibre 

 "really is. Jveceiit observations by means of very much 

 improved and very highly-magnifying microscopes, have 



