408 ELECTRO-PHYSIOLOGY CHAP. 



position of the heart obviates this striking asymmetry in the 

 distribution of differences of potential, which is due to the activity 

 of the cardiac muscle. These experiments also yield di- or even 

 triphasic effects (Fig. 135), and according to Waller's earlier 

 observations, the apex of the heart is invariably negative at first, 

 corresponding with a basal direction of the wave of excitation. 



Owing to the extraordinary sensitivity of the capillary 

 electrometer, and its very rapid reaction, it gives us a direct 

 reading of the action current of striated skeletal muscle, when 

 tetanised. If the capillary electrometer is connected with the 

 secondary coil of an induction apparatus, each interruption or 

 closure of the primary circuit produces a visible movement of the 

 meniscus in the capillary (with a proper adjustment of the coil). 



FIG. 135. Simultaneous record of cardiogram (h, h) and electro-cardiogram (s, e). (A. D. Waller.) 



With Neef s vibrating hammer, the single oscillations fuse into a 

 gray margin, which with reduced strength of current seems to 

 blot out the sharp image of the mercury meniscus, and with 

 increased current rises above it in measurable proportions. On 

 applying a battery current with correspondingly rapid interrup- 

 tions, and uniform direction, the meniscus exhibits a total 

 shifting in the direction of the current. This, like the oscilla- 

 tions, is smaller in proportion as the number of interruptions is 

 greater, and vice versa. In order to detect the gray margin at 

 high frequency, along with the total shifting, greater strength of 

 current is required than at a lower frequency of interruption 

 (Martins, 42). This is important in judging the observations 

 made with the instrument, since a physiological process accom- 

 panied by electromotive action can record itself on the capillary 



