in ELECTRICAL EXCITATION OF MUSCLE 239 



more elegantly demonstrated than in the longitudinal mnscles 

 of Holothuria, With appropriate gradation of strength of 

 current this appearance can be seen at every possible stage of 

 development. The transparent nature of the smooth thin 

 muscles, as well as their promptness of reaction, are very favour- 

 able, and it would be difficult to find any other object in which 

 the local manifestations of excitation at the kathode can be so 

 elegantly demonstrated. The contracted part stands out with 

 extraordinary sharpness and plasticity from the surrounding 

 region as a pale opaque bleb with a peculiar dull lustre ; it rises 

 quickly upon closure of the current, remains unchanged during 

 its passage, and only sinks down again gradually when the 

 circuit is opened. If a minimal current is used for excitation, 

 the contraction appears more and more localised to the immediate 

 proximity of the point of exit, gaming in amplitude with in- 

 creasing intensity of current, until finally the kathodic bleb at 

 the electrode spreads over the whole extension of the muscle in 

 the form of a knotty swelling, and as the muscle-substance is, as 

 it were, drawn up on either side to form this swelling, a not 

 inconsiderable shortening of the entire muscle follows. But it is 

 never so strongly marked as with unipolar anodic excitation. 



In this case, when the current is closed, a marked total con- 

 traction of the whole muscle makes its appearance, so that the 

 movable points of insertion are brought as closely together as 

 possible. 



The muscle appears tensely stretched, and at first seems to 

 be uniformly shortened at every point. This last effect is very 

 striking in view of the reactions previously described for 

 kathodic excitation. There is in consequence not merely no 

 strong local contraction at the anode, but on applying somewhat 

 stronger currents there is an actual interruption of continuity in 

 the muscle. If the electrode (anode) is brought into contact 

 with any point of the free, sharp edge of a muscle, the latter 

 extends itself considerably at closure, and before long a thin 

 transparent point will appear at the electrode (under the magni- 

 fying lens), upon which the fibres next in contact to it break 

 away, and curl back on either side. If the electrode is advanced 

 the whole muscle will sometimes break up transversely, the 

 fibres breaking away from the part in contact, in proportion as 

 the layers are disturbed deeper and deeper. 



