496 



Mr. K. Lucas. 



[June 6, 



biology. As v. Uexkull* remarks : " They had reckoned without their 

 host, and the host's name was Life." To others, the mistake has seemed 

 to lie rather in too exclusive a consideration of the physical side of the 

 phenomena and a consequent neglect of the chemical factors involved.! 

 The aspect of the problem which has appealed to me is that in nerve and 

 muscle we have to deal with a complex sequence of phenomena, some 

 intimately, and some only more remotely concerned with the actual 

 propagated disturbance which is the basis of the nervous impulse. The 

 phenomena which precede, accompany, and follow the propagated disturbance 

 form the chief data on which we have to rely in formulating our hypothesis 

 as to the physico-chemical nature of that disturbance, and we can build on a 

 sure basis only when we have a rigid experimental knowledge of the way in 

 which these phenomena are inter-related. It is perhaps the surprising 

 feature of the past history of this investigation that out of so rich a body 

 of experimental work on the individual phenomena we can gather so small 

 a number of established propositions as to their mutual dependence and 

 inter-relation. And yet it is in this particular problem of the nature of 

 the propagated disturbance, if in any, that the question of inter-relation 

 must play a fundamental part. The disturbance is an unknown change 

 which sweeps along the excitable tissue, and we can come to grips with it 

 only through the conditions by which it is initiated and the measurable effects 

 which it leaves behind. 



Let us turn to this question of analysis and consider first what is the 

 complex of phenomena with which we have to deal. For the purpose of this 

 enquiry I shall choose the artificial case of an isolated motor nerve with its 

 attached muscle, the nerve being stimulated at one point by the passage of a 

 brief electric current along a small part of its length. I choose here just those 

 artificial conditions and that artificial stimulus to which some investigators 

 have objected, and I shall hope presently to justify the choice. The principal 

 and most obvious phenomena consequent upon the application of the stimulus 

 are these. A change of unknown nature travels along the nerve in both 

 directions from the seat of stimulation ; it is this change which I shall speak 

 of as the propagated disturbance and not by the more specialised name of the 

 nervous impulse, because there is evidence that a change of similar nature 

 travels along muscle-fibres also. We are made aware that the propagated 

 disturbance has travelled along the nerve by the changes which it effects in 

 the muscle on its arrival there, but there are two measurable changes in the 

 nerve itself which also follow the application of the stimulus ; these are a 

 * Loc. cit. 



t Holier, ' Zeitschr. f. allg. Physiol./ 1910, vol. 10, Sammelreferat, p. 173. 



