IV 



ELECTROMOTIVE ACTION IN MUSCLE 



401 



which the wave of negativity is already at the leading-off contact 

 nearest the seat of excitation, but has not yet reached the more 

 remote contact. The subsequent stage of no current (and apparent 

 rest) corresponds with the period during which both points led 

 off are at the maximum of negativity (excitation). The positive 

 phase at the end corresponds with the moment at which nega- 

 tivity is already diminishing at the leading-off contact next the 

 seat of excitation, but still obtains unimpaired at the further 

 contact. 



Fig. 127, b, is a graphic record of the time-relations of the 

 excitatory wave in the ventricle of the frog's heart. Easy as it 



FIG. 128. 6, Capillary electrometer. (Fredericq.) 



is with the modern, sensitive galvanometer to demonstrate the 

 P.D. due to spontaneous, or artificially induced, rhythmical 

 activity of the heart, another method that has been much used of 

 late, is still more advantageous ; this is the capillary electrometer. 

 This instrument, invented long ago by Lippman, but first used 

 by physiologists at a much later period, consists essentially of a 

 glass tube, drawn out into a fine capillary (Fig. 128, a and b, A), 

 the open end of which dips into a vessel (B} filled with dilute 

 sulphuric acid. The behaviour of the meniscus in the capillary 

 tube is observed with the microscope. If current enters the 

 capillary in one or the other direction, the surface polarisation 

 will produce a change in the constant of capillarity, with a 



2 D 



