90 C. F. MARSHALL. 



paper. I have, however, recently observed the connection between 

 the network and the muscle-corpuscles described by Eetzius. 



Theory of Muscular Contraction. 



The general conclusions arrived at in the preceding part of the 

 paper are as follows : — 



(1) An intracellular network of a definite character is present in 

 the fibre of striped muscle throughout the animal kingdom. 



(2) This network is developed where rapid and frequent move- 

 ments have to be performed. 



(3) The striped muscle-fibre consists of sarcolemma, network, and 

 sarcous substance ; and, so far as at present determined, there is no 

 other structure present in the fibre (except the muscle-corpuscles and 

 nerve-endings). 



The question now before us is to determine if possible the nature 

 and function of the network, and what relation it bears to the con- 

 tractility of the muscle-fibre. 



Changes in the Network during Contraction. — In order to investigate 

 this point I teased out some perfectly fresh muscle from the leg of a 

 Dytiscus and placed it on an inverted cover-glass over a gas-chamber. 

 Alcohol vapour was then blown over the preparation, when most of 

 the fibres contracted owing to the chemical stimulus. The vapour 

 was passed over the muscle for about a quarter or half a minute. 

 The fibres were then fixed in their contracted state by plunging 

 them into 5 per cent, acetic acid for half a minute, and then treated 

 with gold and formic acid in the usual way. Many fibres were thus 

 obtained completely contracted, and also many fixed waves of con- 

 traction. 



I also made preparations of relaxed muscle from a Dytiscus killed 

 with chloroform. However, as the fibres vary so much in appearance, 

 according as they are more or less pressed out in the gold prepara- 

 tion, comparisons of the muscle stimulated with alcohol vapour, with 

 that reduced by chloroform, though they may give the general effect 

 of the difference, are not absolutely trustworthy. The only way of 

 really proving this point is to examine a fibre, one portion of which 

 is in the relaxed condition and the other contracted, or in other 

 words, a fixed wave of contraction. 



