330 ELECTRO-PHYSIOLOGY CHAP. 



one side to the cross-section (or bones of the pelvis leading off 

 from it), on the other side to the tibial end of the tendon (or 

 tibia itself) ; then at the moment of closing the circuit, which 

 has been broken at any point, the longitudinal current will 

 equalise itself, and will presumably, on leaving the normal 

 muscular substance at the small end of the muscle, discharge a 

 make twitch, if the intensity of the shunt current is sufficient, 

 the resistance in the circuit being as low as possible conditions 

 which are scarcely afforded in the case before us. But if we 

 suppose for a moment that we are really dealing in this case 

 with discharge of a make twitch of the muscle through short- 

 circuiting of its own current, a twitch that was referable to 

 this cause would also be produced if the fraction of the muscle 

 current shunted off' was compensated, or even over-compensated, 

 by a galvanic current sent through the intrapolar tract, i.e. the 

 entire muscle, in an ascending direction finding closure again 

 suddenly at the instant the battery current is broken. In the 

 case in which compensation is complete, and unavoidable secondary 

 effects of the compensating current negligible, the excitation 

 effect will be as great on opening the galvanic current as on 

 the previous closure of the circuit. The experiment is sure to be 

 successful, if the resistance in the leading-off circuit is reduced 

 as much as possible by shortening the intrapolar tract of the 

 muscle (6). 



It is often sufficient to use the lower half of the sartorius 

 only, by killing a segment in the middle of the muscle with 

 heat (artificial thermic section), fastening this point with small 

 needles to a cork plate, and leaving the lower third of the muscle 

 free, weighted only by the dependent tibia. Two unpolarisable 

 electrodes, one of which is placed upon the upper margin of the 

 tract destroyed, while the other (near the tibia) dips into a vessel 

 with concentrated salt solution, serve on the one hand to lead off 

 the muscle current, and on the other to lead in the com- 

 pensating battery current ' from a Daniell cell. In order to 

 graduate the intensity of the latter, a rheochord is introduced 

 into the circuit, which serves as a deriving circuit to the 

 muscle. Provision should be made for opening the circuit at 

 two different points, since the object is to investigate the 

 difference in excitation effect on breaking the main current with 

 simultaneous short -circuiting of the muscle current, and on 



