On the structure of cross-striated muscle. 233 



Conclusions. 



I have already given (p. 190) a general summary of the con- 

 clusions at which I have arrived from this renewed study of the 

 question. It may be well, however, here briefly to recapitulate the 

 principal points which I consider to be well established. 



1. The element of the muscle is the muscle-segment or sarcomere. 



(Muskelkästchen, Krause.) 



2. Each sarcomere is bounded externally by an elastic envelope and 



terminally by a transverse membrane (membrane of Krause, 

 Zwischenscheibe, disque mince). 



3. Each sarcomere contains in its middle a sarcous element (chromatic 



substance, anistropous substance of authors, Querscheibe, disque 

 épais), and at either end a clear interval occupied by semi-fluid 

 hyaline substance (isotropous substance of authors). 



4. The sarcous element is formed of a continuous mass of sarcous 



substance which is perforated by tubules. This structure can be 

 demonstrated in the wing-muscles and indications of it can be 

 found in ordinary muscles. In the wing -muscles and perhaps 

 also in the ordinary muscles the sarcous element is separable into 

 two (some times four?) disks, applied end to end. 



5. In the contracted or retracted muscle the tubules of the sarcous 



element are swollen and shortened, by the passage into them of 

 the hyaline substance. The sarcous element thus increases in bulk 



ceive that the dark dots on Fig. 11 b are really the nodes of this network, but that 

 before the acid has fully acted the lines which join them are not visible. When 

 the substance in the meshes of the network becomes swollen, the lines of the 

 network become evident, and the dots then appear merely as enlargements upon the 

 nodes. I can conceive of no reason why the part which is light in Fig. \\b should 

 have become dark in Fig. 18 a, and vice versa, merely by the more prolonged action 

 of the acid. I find it difficult to believe that Eollett was able to watch the swel- 

 ling up of the individual dark dots upon the surface of the separated disk of muscle 

 and thus to determine that they swell up and become clear areas, while the clear 

 substance in which they lie becomes at the same time converted into a network of 

 dark lines with dots at the nodes of the network — the dark dots first seen be- 

 coming the meshes of the network, those last seen lying at the nodes. Nor does 

 he say that he watched the stages of the process. And if, as it would appear, the 

 decision of the point is a question of inference it seems to me that the more pro- 

 bable account of the change which takes place is that which I have suggested. 



