STIMULATION AND TRANSMISSION 285 



some specific chemical process, whose rate is determined 

 by the characteristic metabolic properties of the tissue, 

 is what preserves the normal resting state of the irritable 

 elements. Thus we may imagine the material of the 

 surface-film as being constructed and replaced as rapidly 

 as it is removed by the chemical (reducing) action of the 

 current; under these conditions the film (with its resting 

 polarization) remains unaltered and no stimulation 

 results. But if the rate of removal exceeds the rate of 

 replacement, the consequence is alteration of the film 

 and stimulation. Conditions of essentially this kind 

 exist in the passive iron model, which shows a similar 

 type of behavior. 



STIMULATION BY CONSTANT CURRENTS 



A typical case of stimulation by the constant current 

 will illustrate how the stimulating effect varies with the 

 duration of the stimulus. The following table from 



,0 



Temperature ca. 15^ 



Duration in t * v /-v . /~ 



Seconds U) Intensity (i) {-y/t 



0.024 0.18 279 



0.021 0.18 261 



0.017 o. 18 234 



0.014 O. 18 212 



O.OT 0.2 200 



0.007 0.23 " 193 



0.0052 0.26 187 



0.0035 0.31 184 



0.0017 0.44 181 



0.00087 0.66 195 



Keith Lucas^ gives results obtained with the sartorius 

 muscle of the frog. Constant currents of known intensity 



'J Physiol., XXXVII (1908), 475. 



