^88 PROTOPLASMIC ACTION AND NERVOUS ACTION 



constant current.' With a P.D. of ten to twenty 

 miUivolts, stimulation occurs at either make or break 

 with the electrodes fifteen to twenty millimeters apart. 

 If we regard the conditions of resistance as similar in a 

 stimulating circuit of this kind and in the normal bio- 

 electric circuit, we may infer that the normal action - 

 current flowing between the active and the resting 

 portions of an excited nerve is effective at a distance of 

 three to four centimeters from the excited area. Other 

 observations, by Hering and others, on secondary 

 stimulation by the demarcation-current, support this 

 conclusion.^ 



The local action-current in the frog's motor nerve 

 reaches its maximum at about .001 of a second after 

 its initiation (at 20°); this is the duration of the rising 

 phase of the action-current curve, according to the 

 observations of Garten and others.^ If we assume that 

 this current, at the moment of reaching its maximum, 

 has a stimulating effect on all resting regions of the nerve 

 within a distance of three centimeters from the active 



^Op.cit. (i9i4),p. 433. 



2 Cf. article just cited, p. 431. See also the recent observations of 

 Spierling (Cremer's Beitrage zur Physiologie, I [1918], Heft 7) and Keil 

 (Z. fiir Biologic y LXXV [1922], i), on the minimal P.D. required for 

 the stimulation of frog's nerves. In Keil's experiments electrodes of 

 varying form were used, and the stretch of nerve traversed by the current 

 varied between 0.5 and 4 cm. in length. The values obtained were of 

 a similar order to those found in my experiments just cited, but showed 

 wide variation. The potentials required with stretches of nerve 2 to 4 

 cm. long varied between 20 and ca. 300 millivolts. 



3 More recent determinations indicate a more rapid rise; cf. Gasser 

 and Erlanger's observations with the cathode ray oscillograph {American 

 Journal Physiology, LXII [1922], 496; also Plaut, Z. Jiir Biol., LXXVIII 



([1923], 133)- 



