i8o THE ORIGIN OF THE NERVOUS SYSTEM 



and activity. As I pointed out in earlier chapters 

 (pp. 70-82), a region of excitation or of rapid oxidation 

 is electronegative externally with respect to unexcited 

 or inactive regions. This means that it is internally 

 electropositive with respect to such regions. Increase 

 in internal electropositivity is then associated with 

 increase in the fundamental physiological activity of 

 protoplasm, though it may also be brought about in 

 other ways as well. Moreover, various lines of evidence 

 and particularly the data concerning electrical stimula- 

 tion indicate that an increase in internal electropositivity 

 of living cells, directly produced by electrical means, 

 generally if not universally determines a condition of 

 excitation or an increase in fundamental physiological 

 activity. It may be that in any stimulation of living 

 protoplasm the primary change is electrical, but whether 

 that is the case or not it is evident that the electrical 

 change is a factor in the change in physiological state. 

 If we admit this, it follows that electrical polarization 

 of a cell may determine changes in its rate of metabolism 

 and in its physiological state in general. 1 We may 

 expect to find the region of increased positivity in such 

 a cell showing increased physiological activity or excita- 

 tion, the region of increased negativity showing decreased 

 activity or depression. As Hyman (1918) has suggested, 

 the phenomena of electrotonus in the nerve fiber appar- 

 ently fall under this head. When a constant current is 

 passed through a portion of a nerve the irritability of a 



1 If the membrane of the unstimulated cell is normally polarized 

 with internal surface negative and external positive, as commonly 

 assumed, an increase in positivity in any region really constitutes 

 primarily a depolarization of that region and such depolarization is, 

 according to R. S. Lillie (see pp. 72-73), an essential factor in stimula- 

 tion. 



