PHYSICO-CHEMICAL BASIS OF TRANSMISSION 389 



area, we have a transmission of stimulating effect 

 through three centimeters in .001 of a second; this is 

 equivalent to thirty meters per second, the usual 

 transmission-velocity at this temperature. The results 

 of this simple calculation are thus in agreement with 

 observation and support the view that transmission is in 

 reality a case of secondary stimulation by the current 





K, K, A, A,, A, R, R, 



5 '^'(0 "5 3 '% 



-> 



Fig. 5. — Diagram of the momentary conditions in a frog's motor nerve axone 

 at 20°. The shaded region marked A, between i?2 and R3, is occupied at the instant 

 under consideration by the excitation-wave, which is regarded as advancing in the direc- 

 tion of the large arrow at the rate of 30 meters per second. Its length, assuming the 

 total duration of the local process (as indicated by the duration of the local bioelectric 

 variation) to be .002 second, is 6 cm. The excitation-process is just beginning at Rj, 

 has reached its maximum at A 10, and has just subsided at R2. The curve represents the 

 variation from the resting potential at different points in the active region; the maximum 

 P.D., at Aio, is ca. 40 millivolts. The regions marked i? are in the resting state. The 

 small arrows indicate the direction of the bioelectric current (positive stream) in a por- 

 tion of the active-resting circuit. Between jRj and R4 its intensity is sufficient to excite 

 the nerve; excitation is thus always being initiated at a distance 3 cm. in advance of 

 the wave front (i.e., up to R4). For a somewhat similar distance RiRi in ihe wake of the 

 excitation-wave the nerve is refractory to stimulation. 



of the local bioelectric circuit. Figure 5 gives a diagram- 

 matic representation of the conditions in a nerve during 

 transmission. 



The course of the current in the bioelectric circuit 

 should be noted; this course is partly extra-cellular, 

 i.e., through the medium,^ and partly intra-cellular; 



^ Part of this current passes through the galvanometer when the 

 action-current is recorded by such an instrument, the remainder through 

 the medium or other extracellular conducting path. 



