CHAP. IX.] THE CONTRACTILE TISSUES. 315 



would become prominent. These in the fresh state are oval, flat- 

 tened, structures containing nucleoli and usually surrounded by, or 

 associated with, a small fragment of unstriated granular protoplasm ; 

 but under the influence of the acid they frequently become shrivelled 

 and linear. In the frog and in the water-beetle they may be found 

 at any depth in the mass of the fibre; while in mammalian muscles 

 they are situated immediately beneath the sarcolemma. 



If the leg of a water-beetle be torn from the body of a recently 

 killed specimen, and its chitinous covering split; and if it be then 

 plunged into absolute alcohol ; portions of fibres may be found in 

 all stages of contraction. Most frequently it happens that in the 

 contracted portion the sarcolemma is raised up from the contrac- 

 tile substance opposite the level of each dim band in the form of 

 a regular fold encircling the whole fibre. In consequence of this, the 

 sarcolemma at the edge of a longitudinal section (or optical longi- 

 tudinal section) of a fibre appears very regularly festooned, the 

 festoons being opposite the ends of the dim bands, and the fixed 

 points opposite the ends of the so-called membranes of Krause. 

 Upon this very remarkable appearance, taken in conjunction with 

 the appearance known as the areas of Cohnheim, Krause has 

 founded his theory that a muscular fibre is partitioned off into 

 superposed prismatic cavities or cells, by horizontal diaphragms 

 which are Krause's membranes, and by vertical walls which are the 

 boundaries of Cohnheim's areas. 



Older views ^ ne lder views of the muscular fibre were chieflv 



Bowman's based upon the effects of certain reagents on the tissue. 

 Sarcous ele- If a muscular fibre is steeped and hardened in a 

 solution of chromic acid or in alcohol and this applies 

 to mammalian as to other fibres the sarcolemma becomes brittle, and 

 the whole contents resolve, at the slightest touch, into innumerable 

 ftnQfibrillae, each of which exhibits an alternation of light and dark 

 parts corresponding with the light and dark bands of fresh fibres, 

 If, again, a fibre has been macerated in hydrochloric acid, the 

 tendency which it exhibits is, not to split longitudinally but rather 

 transversely, through the centre of the principal bright band, thus 

 breaking up into a number of superposed discs called the discs of 

 Bowman. It is clear that, if we imagine cleavage to occur at the same 

 time in both the longitudinal and the horizontal plane, the muscular 

 fibre will become broken up into a number of short prisms, rods, 

 or particles, which may be regarded as the structural units of 

 the dead fibres. To these Bowman 1 gave the name of sarcous 

 elements, several of which are included in each area of Cohnheim. 

 The researches of Bowman remodelled the old representations of the 

 striated muscular fibre, and gave to them a form which they have 

 more or less preserved for forty years. 



1 Bowman, "On the minute structure and movements of voluntary muscle." 

 Phil. Trans. Boy. Soc. Lond. 1840, p. 457. 



