On the structure of cross-striated muscle'. £>27 



of sarcoplasm opposite the middle of the muscle segments — a con- 

 dition which is well known to be not by any means unfrequent (see 

 the figures of Ketzius and many other authors) — or by supposing 

 that the swelling and bulging of the sarcous elements occurs in these 

 cases more prominently or sooner at their ends than at their middle 

 part, in which event the inter-columnar sarcoplasm would become 

 accumulated, not only opposite to and encircling the ends of the seg- 

 ments, but also around their middle. And if, as we have supposed, 

 the swelling is due to imbibition of the hyaline substance of the clear 

 interval by the sarcous elements, the relatively greater bulging of 

 their ends, which are next the clear intervals, might be expected 

 sometimes to occur, and thus to produce this particular condition of 

 the sarcoplasm. It is not, in short, necessary to suppose that the sar- 

 coplasm of the ordinary muscles more than that of the wing-muscles 

 takes any but a passive part in the changes which accompany con- 

 traction of the fibre. 



Contraction- appearances of the living fibres. 



In fresh, rapidly contracting fibres of the leg-muscles of insects 

 it is impossible to follow with any certainty the changes which take 

 place in the striae. This can only be done by the observation of the 

 slow contraction or retraction which takes place usually at one end 

 of a fibre as it is dying; the end in such a case remains persistently 

 contracted, and the condition of contraction gradually involves more 

 and more segments, which one by one appear to move towards and 

 join themselves on to the already contracted part. The process of 

 contraction here described is, no doubt, that which accompanies the 

 entry into rigor mortis and it only differs from the wave-like con- 

 tractions which flit over the perfectly fresh, fibres, in its extreme 

 slowness, which affords an opportunity for the actual changes in the 

 striae to be observed. The most striking difference between the 

 extended (resting) nnd the fully contracted parts of such a fibre (apart 

 from the shortening and bulging of the muscle and the close approxi- 

 mation of the striae) is, as in the wing-muscles, the apparent reversal 



of the stripes. For in the contracted muscle the dark stripes are 



15* 



