STIMULATION AND TRANSMISSION 281 



membranes) are related to the intensity and duration of 

 the polarizing current in the same manner as the stimula- 

 ting effect of a current traversing a living irritable tissue; 

 i.e., to produce a constant polarization current, the 

 product of the intensity of the polarizing current into 

 the root of its duration must be constant.' It thus 

 appears certain that the primary or initiatory process in 

 electrical stimulation is the production of a certain 

 critical degree of polarization at the semi-permeable 

 membranes of the irritable tissue. In other words, the 

 current stimulates by means of its polarizing action, 

 i.e., by producing a potential difference (or by altering 

 an already existing potential difference) between the 

 external and the internal faces of the semi-permeable 

 plasma membranes. 



It should be noted that in itself this result throws 

 little light upon the special physiological nature of the 

 stimulation-process; it merely defines the physical con- 

 ditions under which this process is initiated. The process 

 itself, as just pointed out, has its specific peculiarities 

 which are independent of the nature of the exciting agent. 

 It is, however, an important theoretical advance to 

 recognize that polarization changes are involved in all 

 forms of stimulation. That this is the case is further 

 shown by the invariable participation of bioelectric 

 currents in stimulation processes^; these currents, like 

 any others traversing the tissue, must cause changes of 

 polarization at the cell surfaces. According to the 

 present view, the spread of excitation is due to the 

 secondary stimulation-effects resulting from the polariz- 

 ing action of such currents. 



' Lapicque, Compt. rend. soc. hioL, LXIII (1907), 37. 



