On the structure of cross-striated muscle. 225 



successive sarcous elements. Fig. 42 shows this condition in a fibre 

 in winch the sarcous elements are well stained, while all the rest of 

 the muscle-columns as well as the sarcoplasm between them remains 

 unstained. The condition is precisely similar to that of the wing- 

 column shown at a in Fig. 28. It has been before stated that one of 

 the most valuable features in these alcohol-gold preparations is the 

 diversity of appearance and staining noticeable in different fibres. In 

 some fibres or parts of fibres which may be considered to be charac- 

 teristically stained by tins method, the metal is only deposited in the 

 sarcous elements, which appear of a deep purplish-red colour, strongly 

 contrasting with the rest of the muscle substance, including the sarco- 

 plasm, which remains entirely unstained. In other fibres, in which 

 the sarcous elements are generally rather less darkly coloured, the 

 sarcoplasm, and especially that part of it which forms the transverse 

 networks, has also taken part in the reduction of the gold-salt and 

 shows a greater or less degree of colouration. These fibres, therefore, 

 show with one staining, all the structural points which characterize 

 the leg-musles (Figs. 39, 40, 41, 43, 44). Lastly in the same pre- 

 parations there are always other fibres, and frequently a large number, 

 which exhibit the ordinary gold staining such as is obtained by the 

 acid-gold method, and in these, as before said, only the sarcoplasm 

 with its transverse networks and longitudinal septa is coloured. 



From the description and figures here given of the alcohol-fixed 

 muscle, it is clear that the striation of the sarco styles, therein ap- 

 parent, is dependent upon exactly the same structural conditions as 

 those of the wing-muscles. In each there is a sarcous element formed 

 of chromatic substance occupying the middle of the segment and 

 separated by a clear interval, occupied probably by fluid substance 

 from the membranes which lie between the successive segments. In 

 each the sarcous elements approach that membrane in the retracted 

 (or contracted) condition, at the expense of the clear intervals, and 

 are removed from it in the extended state, with a corresponding in- 

 crease in bulk of the clear intervals. The cross-striation seen in these 

 preparations is, therefore, structural and not obviously modified by 

 optical effects as in the living muscle. 



Internationale Monatsschrift für Anat. n. Phys. VIIL 15 



