iv ELECTROMOTIVE ACTION IX MUSCLE 333 



of the muscle current, the sudden restoration of which, at break 

 of the battery current, produces a make contraction. 



It is indeed a matter of indifference whether the break of the 

 galvanic current occurs in the muscle or battery circuit ; in the 

 latter case it must be taken into consideration that the branch 

 of the muscle current, which is closed by the rheochord, and 

 compensated, or over-compensated, during the passage of the 

 galvanic current, finds its closure at the moment the latter is 

 broken, and hence induces the " spurious break twitch." The 

 theoretical differences in magnitude of twitch in either case are 

 not, however, perceptible, because the contractions are very 

 marked in both cases. 



Since the last-named effects of excitation are of importance in 

 regard to certain facts respecting electrical excitation of nerve, to 

 be described below, we must consider them a little more in detail. 

 If a loop of moist thread is laid round the muscle stretched, 

 to obtain a graphic record of its twitches, in Hering's double 

 myograph so that the current enters anywhere in its continuity, 

 in the close vicinity of an artificial section produced by crushing, 

 while it leaves it again at the pelvic bone, pronounced break 

 contractions, which are almost entirely independent of the length 

 of closure, may be seen directly a weak current is sent in, without 

 regard to the point at which the circuit is opened. If, while the 

 kathode remains in situ at the uninjured pelvic end of the 

 sartorius, the physiological continuity of the muscle is interrupted 

 somewhere near the middle by crushing with forceps, the thread 

 being applied now to one side, and now to the other, of the seat 

 of injury, but always close to its margin, break contractions may 

 be seen in both cases at equal current intensity, in one of the 

 halves divided by the injury, the contraction being always in 

 that half where current enters at the artificial section. If 

 the electrode by which current enters is removed ever so little 

 from the point of injury, the effects of excitation being tested at 

 each new position, it may be seen that the "spurious break 

 twitches " as a rule become weaker, even at points of the normal 

 longitudinal surface that are no more than 2 mm. from the part 

 injured, and disappear altogether as soon as the thread is moved 

 still further, provided closure is effected by the key of the deriv- 

 ing circuit. 



If we are justified in saying that the only fact of importance 



