1 6 THE ORIGIN OF THE NERVOUS SYSTEM 



to some degree of all living protoplasm, except perhaps 

 in certain quiescent conditions; moreover, protoplas- 

 mic transmission may occur from one region to 

 another, even though no differences, either qualitative 

 or quantitative, existed between the two regions before 

 the excitation of one of them by some external factor, 

 i.e., the excitation- transmission pattern may arise, at 

 least momentarily, through the excitation itself. The 

 nature of the process of excitation and transmission is 

 of course dependent upon protoplasmic pattern, but 

 there is no reason for believing that this protoplasmic 

 pattern can of itself give rise to local excitation in the 

 absence of any external action. It appears then that 

 the excitation-transmission pattern is in the final 

 analysis the result of action of an external factor upon 

 a protoplasm. 



Since excitation and transmission undoubtedly occur 

 in all protoplasms it is evident that, while the processes 

 concerned may differ in certain respects in different 

 protoplasms, the occurrence of excitation and transmis- 

 sion is independent of the specific constitution of the 

 particular protoplasm concerned and also independent of 

 the nature of the exciting external factor. Viewed as a 

 whole, the condition which we call excitation, however 

 brought about, appears to be essentially an increase in 

 the rate of living, or at least in the fundamental energy- 

 liberating processes concerned in the life of any particular 

 protoplasm, and transmission consists in the spread or 

 passage of excitation from one region to another, cer- 

 tain dynamic changes in an excited region being the 

 exciting factor for adjoining regions. The excitation- 

 transmission relation is then an energetic, nonspecific 



