PHYSICO-CHEMICAL BASIS OF TRANSMISSION 387 



tions the wave of activation (marked by the darken- 

 ing of the metallic surface) moves slowly upward at 

 the rate of only a few centimeters per second; while 

 in the case of a wire completely immersed in a 

 large volume of acid the transmission is too rapid to 

 follow with the eye, i.e., some hundred centimeters per 

 second. 



Rapidity in the local variation of potential in nerve 

 or other conducting tissue is thus a necessary condition 

 for rapidity of transmission. The table given on page 

 328 shows a general proportionaHty between the rate 

 of development of the bioelectric currents in different 

 tissues and the rate of transmission. The slowing of 

 the bioelectric variation in a particular tissue, by cold, 

 anaesthesia, or fatigue, involves a corresponding slowing 

 in the transmission rate. An exact proportionality is 

 hardly to be expected, because the other properties of 

 the tissue, especially its irritabiHty and its electrical 

 conductivity, are also affected by the change of condi- 

 tions, and other variables enter; but that the rate of 

 electromotor variation is the chief factor determining 

 the speed of transmission seems clearly indicated by the 

 observations cited in the table. 



With regard to the other variable, s, the distance 

 from the active-resting boundary through which the 

 local bioelectric current is effective as a stimulus, definite 

 information is difficult to obtain. I have attempted 

 to estimate this distance in frogs' nerve by measuring 

 the maximal distance between tw^o platinum electrodes, 

 applied to the tissue and having a P.D. similar to 

 that of the bioelectric variation (20 to 40 millivolts), 

 at which stimulation occurs on the make and break of a 



