in ELECTRICAL EXCITATION OF MUSCLE 243 



the formation of a little superficial dint or hollow, the origin of 

 which can be easily explained. It is obvious that when no 

 excitation occurs at the point at which two muscle bundles of 

 equal breadth cross at right angles, while, on the other hand, the 

 arms of the cross beyond the juncture do contract the more 

 strongly in proportion as the section is applied nearer the 

 crossing point a quadratic hollow, bordered by four large swell- 

 ings of equal dimensions, must be developed. An exact dia- 

 grammatic representation of this effect in the excited segment of 

 the worm is from anatomical reasons obviously impossible, but it can 

 often be seen that the segment in contact with the anode is drawn 

 in at that point, and appears to be surrounded by bulging walls, 

 which must be referred partly to the portions of the circular 

 muscles contracting upon themselves in the segment, partly to the 

 equally shortened longitudinal muscles of the next adjacent 

 segment. 



The whole effect can often be brought out more strongly if, 

 with the current closed, two contiguous segments are repeatedly 

 ^troked. at right angles to the direction of the fibres with the 

 brush electrode, upon which both the unexcited surface and the 

 area of contraction become larger, and stand out more sharply 

 from one another. 



Most convincing of all, however, is the local inhibitory effect 

 of the anode (supra) at those points, where either the longitudinal 

 or circular muscles, or both, seem for some reason to be per- 

 manently contracted. The local relaxation of both systems of 

 fibres at the segment in direct contact is then very plain, and 

 quite unmistakable. 



The changes at the kathode are no less striking than at the 

 anode, when the muscular sheath of Lumbricus is excited electric- 

 ally during closure. It would almost be sufficient to say that 

 they express themselves by a direct antagonism, but it is advisable 

 to describe them a little more in detail. 



If attention is directed solely to the segment in contact with 

 the electrode, the antithesis of the anodic and kathodic excitation 

 effects is very striking, and would (without minute examina- 

 tion) suggest that with closure of current at the anode the 

 circular muscles, at the kathode the longitudinal muscles, are 

 exclusively excited. 



It has already been shown, however, that the relations are by 



