398 PROTOPLASMIC ACTION AND NERVOUS ACTION 



successive waves of innervation are received. At each 

 stimulation the decrement in the end-plate is increased 

 temporarily. According to the degree of decrement 

 an impulse received by the end-plate may penetrate 

 the latter and reach the muscle cell with its normal 

 ''intensity," or it may undergo a decrease which may 

 entirely prevent penetration. A grading of the intensity 

 of innervation, depending on the degree of coincidence 

 of phase in the natural rhythms of the two interconnected 

 systems, is thus possible. Forbes has recently appUed 

 this conception to the case of sensory stimulation, and 

 has* expressed the view ''that an unhmited range of 

 sensory graduation might be based on the frequency with 

 which the impulses follow one another in the sensory 

 fibers."^ All of these possibilities should be fully studied 

 and investigated, with a recognition of the probable 

 dependence of excitation and transmission upon the 

 bioelectric processes in the irritable elements. Further 

 discussion of this problem is not possible in this place.^ 

 The role of the bioelectric currents in other physi- 

 ological processes (growth, cell-division, secretion, etc.) 

 is only beginning to be understood, and much further 

 investigation is required. It seems clear, however, that 

 by means of these currents physiological influence 

 may be transmitted rapidly to a distance in many 

 protoplasmic systems other than nerve; and that 

 correlations of activity and function may thus be 

 effected which would otherwise be impossible. Appar- 



* Cf. Forbes, Physiological Reviews, II (1922), 361 (cf. p. 388); Forbes 

 and Gregg, American Journal of Physiology, XXXIX (1915), 172. 



' See Sherrington, "Some Aspects of Animal Mechanism," Nature, CX 

 (1922), 346. 



