On the structure of cross-striated muscle. 213 



columns. These, as we have already seen (Diagram, p. 209 and Figs. 31,37), 

 can readily be ascertained in preparations made by the alcohol-gold 

 method to exhibit longitudinal striae which, as the transverse section 

 of the sarcous element shows, are not rods, but appear as minute 

 hollow tubular canals or pores which everywhere perforate the sub- 

 stance forming the sarcous element. In this, therefore, we have a 

 structure which is clearly comparable to the sponge within our elastic 

 tube. The sarcomere or muscle-segment is itself invested by a delicate 

 envelope which stretches over the clear interval on either side, to be 

 attached to Krause's membrane, and by means of the latter to become 

 prolonged into the envelope of the succeeding segments. Any tension 

 upon the muscle-column will tend to stretch the whole segment but 

 the stretching will show itself most markedly at the level of the clear 

 intervals where the envelope has least solid support. The result of 

 tins will be that the sarcous element will tend to become more sepa- 

 rated from Krause's membrane, and the clear interval will become 

 longer. But if this were all, the interval would become proportiona- 

 tely narrower and would appear as a marked constriction on the 

 muscle-column, which would become more and more narrowed as the 

 muscle-column is more and more extended. This is, however, not the 

 case; the clear interval narrows proportionally with the rest of the 

 segment pari passu "with the increasing extension of the muscle. This 

 can readily be accounted for by remembering that the extension of 

 the sarcous elements will bring lateral pressure to bear upon the 

 contents of the tubular canals which perforate them. Assuming the 

 contents of these tubules to be fluid substance, this will become in this 

 manner expressed from the tubules, and will pass into the clear inter- 

 vals between the sarcous element and Krause's membrane. Hence, 

 with the gradual extension of the muscle the clear intervals will 

 become occupied by more and more fluid which has been expressed 

 from the visible pores of the sarcous element. When the extending 

 force, whatever it may be, is relaxed the fluid would have a strong 

 tendency to pass by capillarity back into the tubules of the sarcous 

 element. The latter would thus not only expand laterally, but also 

 tend to approach the membranes of Krause. And these are exactly 



