in ELECTRICAL EXCITATION OF MUSCLE 207 



of current through the muscle as long as is required, without any 

 fear of the intensity of the current diminishing in a perceptible 

 degree ; and this is facilitated by the study of the persistent 

 opening contraction. It is at once seen that first one and 

 then the other half of the muscle, according to the direction of 

 the current flowing through it, becomes permanently shortened 

 (Fig. 88), and that on strengthening the current the persistent 

 contraction increases considerably (Fig. 78), without any transfer 

 to the other (anodic) half. If a muscle that is not too tensely 

 stretched is examined with the unaided eye or magnifying lens, 

 the local swelling of the ends of the fibres may be plainly 

 seen, even with minimal currents, after the closure twitch has 

 expired, as described by Engelmann. The contractile substance 

 almost appears to flow suddenly, as it were, at the moment of 

 closure, from the region round the kathode to the kathode itself, 

 and to accumulate there. In muscles that have been exposed to 

 excess of cooling, by which their conductivity has suffered, it can 

 be seen directly, as shown by Hermann, that the muscle is drawn 

 at closure towards the kathode, on opening towards the anode. 

 The swelling only affects the peripheral ends of the fibres, 

 immediately before they pass into the tendon. Even with 

 moderately great tension of the muscle, a small swollen expan- 

 sion appears, which persists unchanged throughout the entire 

 duration of a persistent passage of current. On strengthening 

 the excitatory current the persistent closure contraction increases 

 considerably in amplitude, without however losing its localised 

 character, even with high intensity of current. The sections 

 which lie collectively between the kathode and the centre of the 

 muscle never remain in persistent contraction during the passage 

 of current. In judging of the spatial extension of a manifesta- 

 tion of contraction in muscle, great care must be taken not to 

 confound the true shortening with the merely passive contraction 

 of adjacent parts. A very simple method of artificial observation 

 consists in marking the surface of the muscle with signs, which 

 move in opposite directions when the muscle shortens, and thus 

 indicate the spatial extension of the contraction. We have found 

 it convenient to paint the whole muscle with transverse bands of 

 Indian ink, at right angles to the direction of the fibres, so that 

 the distance between each pair of cross-Hues, traced with a fine 

 bristle upon the dry surface of the sartorius, was about -|- mm. 



