194 



ELECTRO-PHYSIOLOGY 



CHAP. 



corresponding with a single weak induction current, or " current- 

 impact," does not eventually produce a twitch, as is the case in a 

 variation of. the form (d), because the low duration of current is 

 compensated in the latter by greater intensity. On the other hand, 

 a variation of the form (e) may act as a stimulus on the same 

 preparation which is unexcited by (c), because in this case the 

 greater duration compensates the lower intensity, and the same may 

 also apply to a variation with less steepness of rise and fall (/). 

 The striking predominance of the excitatory effect of the 



FIG. 81. a, 6, c, Different forms of variation curves of current intensity. (A. Fick.) The 

 abscissae indicate the time in seconds, the ordinates the strength of current. 



break induction current is usually referred to the different rise 

 of current intensity, and applies as much to smooth as to striated 

 muscle, and indeed to nearly all irritable tissues. But since the 

 experiments in this direction have till now been confined almost 

 entirely to motor nerves, it will be more convenient to postpone 

 the discussion of these facts until the scanty experimental data 

 which exist in regard to dependence of excitation on the exact 

 form of the curve of variation of current intensity can be brought 

 forward. 



. The reaction of cardiac muscle to the constant current, as 

 in many other respects, is exceptional. Ever since Eckhardt 



