STRUCTURE OF STRIATED MUSCLE. 549 



declare myself in favour of Heppner 's views. I do not, how- 

 ever, consider the matter to be finally settled. Since Heppner 

 conducted his researches in my laboratory I have repeatedly 

 and most carefully worked over the subject of the structure of 

 muscular fibres, but have up to the present time arrived at no 

 positive conclusion upon the point in question. 



My researches have been made exclusively upon fresh mus- 

 cular fibres, which have been placed under the covering glass 

 without the addition of any fluid, and compressed more or less 

 gently by the insertion of a layer of cement between the 

 margins of the cover and the slide. I have also not avoided 

 the object which Hensen so strongly charges Heppner in a 

 recent publication as having neglected ; but have for the most 

 part used the muscles of Hydrophilus, because, as several 

 distinguished fellow- workers have pointed out, the muscles of 

 this animal are extremely favourable for this purpose. 



When examined with Hartnack's lens, No. 15, it may be 

 seen, in cases in which the still living muscular fibres appear 

 transversely striated, that the intermediate substances (in the 

 sense of Rollett) are not homogeneous. It may in fact readily 

 be shown, especially when they are not very slender, that dark 

 granules lie in a clear matrix. In many cases I could only 

 count two granules in the length of a single disk. Their 

 arrangement in the clear matrix also varies: sometimes the 

 whole intermediate substance appears in the form of a finely 

 granular zone of protoplasm ; sometimes it is partially free 

 from granules, or these are thinly and irregularly scattered. 

 It has been stated by many observers, that the intermediate 

 substance appears, according to the focussing, sometimes clear, 

 sometimes dark ; but, so far as regards the appearances pre- 

 sented with the No. 15 lens, I can state positively that the 

 intermediate substance is always dark, when in perfect focus, 

 at the point where the granulations are situated, whilst it is 

 always clear where there are no granulations, clearer even 

 than the chief substance. The chief substance remains rela- 

 tively dull at all focuses. 



The appearances presented by the muscular fibres of Hydro- 

 philus, so long as they still move actively, are extraordinarily 

 variable. In those which only appear transversely striated, the 



