TRANSMISSION AND CONDUCTION 223 



Portions of the circulatory system of various animals, 

 which transmit active contraction waves in a particular 

 direction, also probably arise as physiological gradients. 

 In fact we shall probably find that all organs which are 

 axiate as regards their special function as well as organ- 

 isms and organs which are structurally axiate represent 

 physiological gradients. The gradient is, in short, as I 

 have attempted to show, the physiological basis and 

 starting-point of the organismic type of relation, and 

 structural and functional relations are merely different 

 aspects of the general pattern. 



THE "ALL-OR-NONE' : PRINCIPLE IN NERVOUS 



CONDUCTION 



The "all-or-none" principle or so-called law main- 

 tains that intensity or degree of excitation is independent 

 of the strength or intensity of the stimulus for all stimuli 

 above the threshold, the minimum stimulus which 

 brings about reaction. In other words, in tissues which 

 show the u all-or-none' : type of reaction, all stimuli 

 above the threshold produce maximal excitation. Lucas 

 (1917) has concluded from his and Adrian's investiga- 

 tions that the nerve fiber, the axon, shows this type of 

 reaction in the vertebrates. 



Both Lucas and R. S. Lillie conclude further that if 

 a conducting tissue, e.g., the nerve fiber, reacts according 

 to the "all-or-none' : principle, it must necessarily be 

 capable of conducting to an indefinite distance without 

 decrement an excitation once initiated. This conclu- 

 sion is correct, provided the maximal excitation is the 

 same in degree or intensity at all points of the path, hi 

 other words, if all points of the path are in the same 



