278 ELECTRO-PHYSIOLOGY CHAP. 



situation of the electrodes), that the physiological kathode, or 

 anode, must possess a considerable extension. In the one case, 

 therefore, if a branch of the polarising current diverges into the 

 exciting circuit, the physiological kathode of the test current 

 falls upon points of fibres that are already kathodic ; at other 

 times the contrary occurs, since the kathode of the test current 

 then coincides with anodic points. The effect of the test current 

 naturally depends upon its direction. Since the distribution of 

 current into the two circuits depends solely upon the ratio of 

 resistance, it is possible, in any given case, to throw such a resist- 

 ance into the exciting circuit that the resistance of the short tract 

 of muscle between the corresponding electrodes shall be minimal, 

 to avoid a branching of the constant current into the exciting 

 circuit (Hermann, Handl. II. i. p. 44). The experiment is 

 arranged as follows : Two non-polarisable electrodes fastened 

 to a movable holder, are applied in the usual manner to different 

 points of a sartorius, stretched in Hering's double myograph. 

 The make induction current is exclusively used as the test 

 stimulus, and is led in by threads moistened with physiological 

 NaCl solution, in order to interfere as little as possible with the 

 changes of form in the muscle. The length of the intrapolar 

 tract is about 3-4 mm., and its resistance is therefore 

 negligible in comparison with that of a glass tube 2 in. long by 

 0'5 cm. in diameter, filled with very dilute CuS0 4 solution, 

 introduced into the primary circuit. The twitches are recorded 

 upon a smoked surface, one electrode of the double myograph 

 being permanently fixed, while the other is in connection with 

 a writing-point. The intensity of the polarising battery current 

 is graduated as required by a rheochord. The closure and 

 opening of the constant current is effected by a mercury key 

 introduced between the rheochord and battery (2 Dan.). If the 

 polarising and exciting current have the same direction (both 

 descending), the case is, in the first place, conceivable in which 

 the points of exit fall together, the negative test electrode being 

 applied to the stump of the tibia, while the other is in contact 

 with the end of the sartorius. In this case there will be marked 

 alterations in the excitability (to be described below). Quite 

 other results occur, when both exciting electrodes are placed in 

 the continuity of the muscle. According to v. Bezold, it might 

 be expected that during the closure of a very weak current, a 



