242 ELECTRO-PHYSIOLOGY CHAP. 



in which the contraction of the circular muscles is com- 

 paratively less developed than the contraction of the longitudinal 

 muscles, on either side of the ring in contact with the anode, 

 so that the latter is only constricted in an inferior degree ; 

 nor does the height of this segment diminish, although this is 

 in a marked degree characteristic of the neighbouring segments. 

 Moreover, there is another feature in every case, which seems 

 to be of importance in the conception of the anodic effects of 

 excitation. 



If the contraction of the circular muscles is pronounced, the 

 excitation appears to be developed with approximate uniformity 

 at every point of the muscle -ring, as though the process of 

 excitation, i.e. contraction, starting from the anode, was trans- 

 planted on either side from section to section. This idea at 

 once suggested itself from an unprejudiced consideration of the 

 effects of excitation. But if the ring-shaped constriction is not 

 maximal, so that the part of the segment in contact with the 

 anode remains visible, it can usually be seen (at least under 

 the magnifying lens) at the actual point where the current enters, 

 as well as in the immediate proximity, not only that the 

 contraction of the longitudinal muscle is wanting, but that there 

 is not even any perceptible contraction of the circular muscles. 

 This is especially plain when the surface of the worm has dried 

 from evaporation, and consequently become less elastic. It then 

 appears very elegantly that fine cross -wrinkles arise from the 

 involution of the epidermis on the surface of the contracted 

 ring ; these are plainly visible at either side of the electrode, but 

 fail altogether in the immediate proximity of the anodic contact. 

 The electrode must be only just moist in this experiment, so as to 

 avoid wetting the seat of excitation. In every such case a directly 

 relaxing (inhibitory) effect of the anode may be demonstrated, 

 if the contact is pushed, during closure of the current, towards 

 any point of the excited segment in which the contraction has 

 already produced obvious transverse wrinkles. As soon as such 

 a spot is brought into contact with the anode it begins to smooth 

 itself, and gives the impression that notwithstanding the con- 

 traction of adjacent parts of the muscle-ring relaxation and 

 lengthening occur at the actual seat of contact. It is by no means 

 rare in longitudinal as in circular muscles, to find this failure 

 of contraction at the anode itself, still more plainly marked by 



