414 



SCIENCE 



[N. S. Vol. XLI. No. 1055 



ready explanation without the help of the 

 hypothesis of antidromic nerve impulses. 

 Furthermore, if the axon reflex is the 

 foundation of this inflammatory reaction, 

 we may well investigate other reactions 

 which in the past have been classed as re- 

 flexes, but upon inadequate evidence. So 

 long as the reflex was supposed to be the 

 only means by which stimulation of a pe- 

 ripheral sense organ can evoke a non-voli- 

 tional reaction in another organ, all such 

 reactions have been classed as reflexes, and 

 this quite frequently without experimental 

 proof. 



CONDITIONED AND UNCONDITIONED REFLEXES 



The main purpose of this paper is to em- 

 phasize neglected aspects of nervous action. 

 Hence our treatment of reflexes, properly 

 so-called, will be confined to emphasizing 

 the fact that we probably include in the 

 category of the reflex two entirely different 

 kinds of nervous reaction. 



It is an interesting fact that so common 

 a phenomena as reflex action is somewhat 

 loosely defined in our thinking. One will 

 call it an action brought about by the stimu- 

 lation of efferent neurones by one or more 

 afferent neurones ; another will add to this, 

 "without the intervention of the will"; 

 another will add, ' ' without the causal inter- 

 vention of consciousness ' ' ; while still an- 

 other will add, "without the causal inter- 

 vention of consciousness or the will." 

 These four definitions are by no means 

 identical, as I hope to show. All of them 

 have in common the fact of stimulation of 

 efferent by afferent neurones, stimulation 

 being supposed to include both excitation 

 and inhibition, and it being assumed that 

 any number of intermediate neurones 

 (first, second and third order, etc.) may be 

 interposed between the afferent and the 

 efferent nerves concerned. All would ex- 

 clude the will from any causal connection 

 with the reaction, and this leaves as the 



chief point of difference in the above defi- 

 nitions the question whether we should ex- 

 clude from the category of reflex action all 

 cases where the nervous processes con- 

 cerned in consciousness play, or seem to 

 play, a causal role in the chain of events; 

 for there are nervous actions which are in 

 no sense volitional ; which have an afferent 

 and an efferent side, and hence resemble 

 reflexes; but in which we encounter the 

 nervous actions concerned with conscious- 

 ness. The example which at once occurs to 

 us is the so-called psychic secretion of saliva 

 and gastric juice. To these we would add 

 the no less striking case, brought to our 

 attention by Cannon, of the stimulation of 

 the secretion of adrenalin as the result of 

 the major emotions of fear and anger. In 

 all these cases there is the absence of con- 

 scious intention; indeed, the subject is un- 

 aware that the act of secretion is taking 

 place; and yet the conscious process is the 

 starting point of the efferent discharge. 

 Shall we or shall we not call such actions 

 reflex actions ? 



The answer to this question is, of course, 

 entirely a matter of arbitrary definition. 

 If we exclude the causal interposition of 

 consciousness'' from the reflex, such reac- 

 tions are not reflexes; if we do not exclude 

 it, they are. The decision in such an arbi- 

 trary matter, moreover, is determined on 

 purely utilitarian grounds. Definitions 

 exist only to insure clear thinking by keep- 

 ing separate and distinct those things hav- 

 ing some fundamental point of difference. 

 Thus many would have us believe that there 

 is no really fundamental difference between 

 reflex and volitional acts; that the efferent 

 discharge in the simplest reflex is accom- 

 panied by a momentary flash of something 

 that corresponds to conscious intention; 



'' To avoid a cumbersome expression, the word 

 ' ' consciousness ' ' is frequently used for the ' ' nerv- 

 ous events connected 'with the state of conscious- 

 ness. ' ' 



