INHIBITION AND CARDIAC VAGUS 119 



There are " organisms " of the social kind in continuous 

 activity, with no complete pause, not even such a pause 

 as that of the heart. Such an organism is a ship at sea. 

 When one watch comes on deck the other goes off. From 

 the time of leaving one port to reaching another this con- 

 tinues. There is no moment at which part of the crew is 

 not in " tone," ready for action, or in actual work. A ship 

 has been evolved ; it has grown up, it has its reactions, 

 which we call sea customs. Although the two " watches " 

 or parts of the crew are separate, and usually possessed of a 

 certain jealousy or " hostility " to each other, they are con- 

 nected by innumerable bonds of habit and custom. When 

 one goes on deck in fine weather the other is " inhibited." 

 Does such inhibition arise centrally ? Although it may do 

 so in some cases it is mostly a pure reflex phenomenon. 

 One activity replaces the other automatically. It seems 

 to me that such a case supplies more than a hint for what is 

 known as "reciprocal innervation." When two muscles 

 have been evolved together, fulfilling opposite functions, 

 it is impossible not to imagine definite relations and con- 

 nections between them. The very activity of one implies 

 the inactivity of the other. And the actions of decerebrate 

 animals prove it. That the central system in a ship ensures 

 definite direction of the whole ship we know, but in the lower 

 functions excitations and inhibitions proceed automatically, 

 and it is of physiological interest to note that overmuch 

 central interference with such functions produces symptoms 

 which rapidly tend to become pathological. It is well 

 understood at sea that " central " interference is only 

 justifiable in abnormal conditions. Thus so long as the 

 crew function normally no officer enters the fo'c'sle except 

 on stated occasions of inspection. If he did it would 

 be greatly resented. Perpetual unevolutionary stimuli 



