On the structure of cross-striated muscle. 219 



Production of the cross-striae of muscle and changes in 



contraction. 



Finally there remains to be considered the mode of production of 

 the cross-striated appearance of muscle and the change which this 

 undergoes during contraction. For this purpose again it will be best 

 to begin with the consideration of the wing-muscles, since we are here 

 able to deal with simple elements, viz: with isolated muscle-columns, 

 whereas in the ordinary muscles the appearances are complicated by 

 the peculiar arrangement of the sarcoplasm between the columns. 



An examination of the wing-muscle fixed by alcohol and stained 

 by haematoxylin or by gold, is sufficient, at the first glance, to nega- 

 tive the idea that the alternate dark and light striae are merely 

 optical effects caused by the moniliform shape of the muscle columns 1 ) 

 or in any other analogous manner. The staining of the sarcous 

 elements and the contrast they present with the clear intervals which 

 separate them from the membranes of Krause, afford unmistakable 

 evidence that they are composed of different material. 2 ) (see figures 28 

 to 44.) 



*) Eaycraft. Quarterly Journal of Micr. Science. April 1881. 



'-) I have preferred to leave altogether out of account the different optical 

 properties which are exhibited by the striae, as regards single and double refraction, 

 because such differences of optical property cannot be taken as evidence of difference 

 of material. The demonstration of the fact that they may entirely depend upon 

 differences of „stress" which, so far as the tissues are concerned, we owe to Ranvier, 

 renders all conclusions as to structure which are derived only from such optical 

 differences nugatory. I have therefore determined not to encumber the present 

 account of the structure of muscle with a narration of these optical appearances. 

 For such observations when taken by themselves prove nothing definitely, and even 

 assuming that they could be rightly used to elucidate the structure of muscle, they 

 add little or nothing to what can be learned from the study of stained preparations. 

 And although postmortem changes and the action of reagents produce important 

 changes iu the optical properties of different parts of thü muscle-segment, we are 

 entirely ignorant as to the actual meaning and cause of these changes. On this 

 account I have, in all the descriptions given, avoided the use of the terms „isotro- 

 pous" and „anisotropous" substances; but those who are acquainted with the litera- 

 ture of the subject will at once find in the designations which I have adopted 

 synonyms for those terms in the sense in which they are usually employed by 

 authors. 



