CHAP. Ill 



ELECTRICAL EXCITATION OF MUSCLE 



175 



found the widest application in excitation experiments, several 

 different forms having been adopted. When it is required to 

 lead a current into a striated muscle, the shifting of the contract- 

 ing muscle under the electrodes in contact with it is a ready 

 source of fallacy, which can only be avoided where the electrodes 

 are fixed to the muscle, or bones into which it is inserted, so 

 as to follow every movement. Hering was the first to construct 

 non-polarisable, shifting electrodes for the frog's sartorius, which, 

 from its regular structure of parallel fibres, is singularly 

 appropriate to such experiments, and is easily prepared without 

 disturbing its natural relations with the bones of the leg and pelvis : 



m 



FIG. 71. Apparatus for investigating the polar effects of the electrical current in muscle 

 (double myograph). A non-polarisable movable electrode. (Hering.) 



these electrodes serve for a variety of purposes (1). " A 5'5 cm. 

 glass tube (Fig. 71) is provided at the upper end with a split 

 brass holder, carrying two diametrically opposite points, which fit 

 into the holes of a pivot, so that the vertically dependent tube may 

 easily turn on the points, and oscillate from them. The pivot is 

 fixed to a brass ring (m), which can be moved along a horizontal 

 rod (q) of bone or ebonite. A short ebonite cylinder (Ji) is pushed 

 over the lower end of the glass tube, the opening of which is the 

 continuation of the bore of the tube, and is transversely pierced 

 in such a way that a slender bone like the tibia or os ileum of the 

 frog can be passed through the hole, and fixed by a screw. A 

 small amalgamated zinc rod is dropped into the tube from above, 



