in ELECTRICAL EXCITATION OF MUSCLE 241 



filter-paper or salt clay, and is in contact with one (the indifferent) 

 electrode, while the other (a fine brush electrode) is placed on the 

 centre of the dorsal surface of one of the broad segments at the 

 anterior end of the worm, a sufficiently strong current given 

 maximal paralysis of voluntary movements and reflexes will 

 throw the segment in direct contact (and that segment only) into 

 circular constriction, in which state it will persist as long as the 

 current remains closed. If the current is strong and the ex- 

 citability of the muscle high, this constriction (produced by 

 contraction of the circular muscles) may almost obliterate the 

 lumen of the body-cavity, thus of course producing more or less 

 passive distortion of the surrounding parts, and of the immediately 

 contiguous segments in particular. The excitation effect, however, 

 remains localised in the segment in direct contact, and there is no 

 propagation of contraction in the form of a peristaltic wave. 

 But along with this passive contraction of the adjacent portions of 

 the muscular integument, there is rarely wanting an active 

 decrease in height of the contiguous segments, due to the contrac- 

 tion of the longitudinal muscles, which is most strongly marked 

 in the immediate proximity of the constriction, and gradually 

 diminishes outwards, so that it is never perceptible at the 

 whole periphery of the segments affected, but only at the side 

 corresponding with the seat of excitation. Hence we must be 

 dealing with a unilateral contraction mainly active, but in part 

 passive also of the body-rings adjacent to the anodically excited 

 segment. The proof that this is a genuine shortening of the 

 longitudinal muscles (apart from the spatial extension of the 

 changes produced at either side of the circular muscle contrac- 

 tion, which may be very considerable) lies unquestionably in 

 the important decrease in height of the segments affected, and 

 the only doubtful point is how the directly excited segment 

 itself reacts under these conditions. It is prima facie evident 

 that there is an often maximal excitation of the circular 

 muscles, while perceptible shortening of the longitudinal muscle 

 on the other hand is everywhere absent. This cannot perhaps 

 be determined only from the fact that there is no apparent 

 decrease in the height of the muscle-segment concerned, since 

 the two layers of muscle work antagonistically both in regard to 

 changes in length (height), and in breadth, of the segment, but 

 on the other hand it is indisputable that cases may be observed 



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