CHAPTER XII 



CERTAIN FEATURES OF TRANSMISSION AND CON- 

 DUCTION IN RELATION TO THE PHYSIO- 

 LOGICAL GRADIENTS 



In chapter iv the part played by excitation and trans- 

 mission in originating and establishing the physiological 

 gradients was discussed. In chapters vi-xi it was 

 shown that the physiological gradients afford a general 

 physiological basis for the localization, the course of 

 differentiation and the general plan of structure of the 

 nervous system as a whole, as well as for tentative con- 

 clusions concerning the origin and development of 

 neuron pattern. Since there can be no doubt concern- 

 ing the close relation between nervous structure and 

 nervous function, i.e., the conduction of impulses, and 

 since the facts indicate that the physiological gradients 

 originate in excitation and its protoplasmic transmis- 

 sion, there is every reason to believe that these gradients, 

 once established, must play a part in the development 

 of the more or less specialized forms of transmission, 

 which are usually called conduction. The gradients 

 provide, first of all, a mechanism for giving conduction 

 a more or less definite, or at least a preferential, direction 

 and thereby for determining in some degree the physio- 

 logical relations to each other of various parts. The pur- 

 pose of the present chapter is to call attention to certain 

 facts in connection with the transmission or conduction 

 of impulses in paths which do not show any distinguish- 



206 



