14 DAVID P. C. LLOYD 



those of Wedensky (1903) on inhibition of nerve impulses in which effect 

 was clearly a consequence of action. Thus we enter the period under con- 

 sideration with two alternative ideas prevalent: that of inhibition as an 

 action and that of inhibition as a consequence of action. 



An hypothesis as to mechanism of inhibition was presented by Keith 

 Lucas (1917) who set forth his philosophy in these often quoted paragraphs: 



"Are we to suppose that the central nervous system uses some process different from that 

 which is the basis of conduction in peripheral nerves, or is it more probable that the 

 apparent difference rests only on our ignorance of the elementary fact of the conduction 

 process? If we had a fuller knowledge of conduction as it occurs in peripheral nerves, 

 should we not see inhibition, summation, and after-discharge as the natural and 

 inevitable consequences of that one conduction process working under conditions of 

 varying complexity?" 



and 



". . . we should inquire first with all care whether the elementary phenomena of con- 

 duction, as they are to be seen in the simple motor nerve and muscle, can give a satis- 

 factory basis for the understanding of central phenomena; if they cannot, and in that 

 case only, we shall be forced to postulate some new process peculiar to the central 

 nervous system." 



Keith Lucas notes that McDougall and von Uexkiill had put forward 

 hypotheses which account for the phenomena of inhibition by 



"postulating a process unknown to the student of nervous conduction, namely, the 

 passage along nervous paths of a something which can stay and accumulate in one 

 part or another of the nervous system." 



Parenthetically, this notion sounds quite modern to our ears today. In pre- 

 senting his own hypothesis, Keith Lucas gives reference to Verworn and 

 Frohhch as predecessors, at least in part. 



Such was Keith Lucas's prestige that much thought on inhibition for a 

 long time concentrated on inhibition as a consequence, or secondary effect, 

 this despite the blow seemingly dealt when the theory of decremental con- 

 duction, a key point in Keith Lucas's specific hypothesis, was held to be 

 invalid (Kato, 1924, and others). However, throughout the works of Sher- 

 rington there can be no doubt but that inhibition as a direct action is the 

 preferred hypothesis, and the numerous facts uncovered by him were justifica- 

 tion for the point of view. To quote one point made (Eccles and Sherrington, 

 1931): 



"If the inferences drawn from the present series of experiments are correct, namely, 

 that the inhibition produced by any particular impulse persists for as long as 50 o, 

 and that excitation and inhibition mutually inactivate each other, then an explanation 

 in terms of the Wedensky effect appears to be impossible." 



Although these telling blows militated against the specific hypothesis of 

 Keith Lucas, they did not for long defeat the more general concept of inhibi- 

 tion as a consequence of action, for in the discovery of the subnormal period 



