640 



// MANUAL OF PHYSIOLOGY 



d> 



membrane. The sarcomere is thus length- 

 ened and narrowed. While the existence 

 of Schafer's pores is not admitted by all 

 observers, there is a pretty general agree- 

 ment that the sarcomere, like the cytoplasm 

 of an amoeboid cell, does consist of two 

 substances, one of which (the hyaloplasm 

 of the cell, the clear material of the sarco- 

 mere) interpenetrates the other (spongio- 

 plasm of the cell, substance of the sarcous 

 element) ; and that in relaxation the clear 

 fluid passes from the sarcous element to 

 the ends of the sarcomeres, whereas in con- 

 traction it passes in the reverse direction 

 into the sarcous elements. Whether the 

 fluid passes into and out of the meshes of 

 an actual network, or along actual physical 

 pores in the sarcous element, or whether 

 it is transferred by some process like mole- 

 cular imbibition (p. 398), need not be dis- 

 cussed here, since it is not definitely known. 

 The fundamental question by what process 

 the transference is determined when the 

 muscle is excited also remains unsettled. 

 So far as is known at present, it is probable 

 that the mechanical energy of the contract- 

 ing muscle must be derived from the trans- 

 formation of chemical energy into one of 

 three forms : energy associated with os- 

 motic processes, energy associated with im- 

 bibition, and energy associated with changes 

 of surface tension. It is not difficult to see 

 that a sudden increase in the osmotic con- 

 centration in the sarcous element, due to 

 the breaking up of large molecules or col- 

 loid aggregates into small molecules, or the 

 liberation of electrolytes from the colloids, 

 might lead to the rapid passage of water 

 into it from the bright bands. A sudden 

 change of permeability of the sarcous 

 elements for dissolved substances in the 

 clear fluid would have a similar effect. 

 The same is true of a change in their 

 power of imbibition. But, according to 

 Bernstein, it is scarcely to be supposed that 

 the extraordinarily rapid movement of 

 water molecules which must occur in con- 

 traction can be accounted for either by 

 osmosis or by imbibition. A more plausible 

 theory is that the surface tension say 

 between the substance of the sarcous ele- 

 ment and the clear fluid is altered. Some 

 writers assert that in contraction there is 

 such a transference of substance between 



the light and dim stripes that the former becomes dim, and the latter 

 light. This so-called reversal of the stripes is not really a re- 

 versal in the sense of being a bodily exchange of the whole of the 



lc/8 

 cZ? 



FIG. 226. CRAB'S MUSCLE 



IN DIFFERENT STAGES 



OF CONTRACTION (AFTER 

 RUTHERFORD). 



Three fibrillae are shown : 

 r, complete relaxation ; /, 

 complete contraction ; b-b 10 , 

 sarcous elements ; d-d 9 , 

 Dobie's granules ; /, Flogel's 

 granules. 



