THE METHOD OF TRIAL AND ERROR. 249 



to all ; as a consequence or concomitant of this physiological state a 

 negative reaction follows. In man this physiological state is accom- 

 panied by pain. The common physiological state might then properly 

 receive a name which brings out its relation to the state accompanied 

 in man by pain ; for example, J. Mark Baldwin's " organic analogue 

 of pain." 



We have left under this formulation the fundamental question as to 

 how a set of agencies that are quite heterogeneous from a chemical or 

 physical standpoint can produce a common physiological state. This 

 question is, of course, of precisely the same order of difficulty as that 

 which asks how the same heterogeneous set of agents can produce a 

 common state of consciousness, namely, pain. We therefore lose noth- 

 ing, so far as this problem is concerned, by substituting *' a common 

 physiological state" for "pain" in dealing with the subject. But to 

 attempt to deal with the problem of negative reactions in the lower 

 organisms without recognizing that they are conditioned in the same 

 way as the negative reactions of man without admitting the existence 

 of some physiological state analogous to that which is accompanied by 

 pain in man, is, I believe, to close one's eyes to patent realities. 



We have seen above that the method of trial and error involves some 

 way of distinguishing error. But do not some of the facts indicate 

 that it involves, at least sometimes, also some way of distinguishing the 

 opposite of error ; that is, what we may call success? For most of the 

 reactions of the infusoria this seems not necessary, for what the organ- 

 ism does when successful is merely to continue the condition in which 

 it finds itself at the time. There is then no objective evidence that a 

 stimulus is acting at this time. In these organisms it seems to be chiefly 

 the injurious or negative stimuli that induce a motor reaction. But 

 consider the floating Amoeba, which sends forth pseudopodia in all 

 directions. Finally one of these pseudopodia comes in contact with 

 a solid, and to this stimulus the Amoeba reacts positively. Now all 

 the other pseudopodia, though the external conditions directly affecting 

 them remain the same, become retracted, and the whole Amoeba moves 

 toward the pseudopodium in contact. This withdrawal of the other 

 pseudopodia requires for its explanation a change in physiological state 

 which can be due only to the success of the pseudopodium that has 

 come in contact with a solid. There is certainly no basis here for con- 

 sidering the reaction as due to an " organic analogue of pain" ; possi- 

 bly a case could be made out, on the other hand, for a physiological 

 state corresponding to that which conditions pleasure in ourselves. 

 Possibly similar considerations hold for the positive reactions of other 

 organisms infusoria, etc. to solids. 



There appears to be a similar state of affairs in the righting reaction. 



