98 



THE ORIGIN OF THE NERVOUS SYSTEM 



In this figure xy is the gradient in electronegativity 

 characteristic of the physiological gradient. Let us 

 suppose an excitation to occur at a with' an increase in 

 electronegativity ab. It is evident that the' current 

 produced by excitation at a will be compensated at d 

 by the current of the physiological gradient, but if 

 points on the gradient above a increase the strength of 



Fig. 7. — Diagram illustrating transmission up a gradient; for explana- 

 tion see text. 



the excitation current the excitation may be trans- 

 mitted to a higher level e and so on. 



An excitation at the level a which increases the 

 electronegativity to c will produce electrical effects at 

 all levels up to x and if the excitation brought about by 

 this current at levels above a increases this electro- 

 negativity still further, the excitation ac may be trans- 

 mitted all the way to the high end of the gradient and 



