THE METHOD OF TRIAL AND ERROR. 247 



when there is error the organism goes back and tries a new direction, 

 or a whole series of new directions. 



But what constitutes "error" ? This is a fundamental question for this 

 method of behavior. Why does the organism react to some things by 

 turning away and trying new directions, to others not? Why do they 

 react thus on coming to certain chemicals, and on leaving others? 

 Why do they react thus on coming to a strong chemical, and also on 

 leaving a weak solution of the same chemical? Why does the same 

 organism react thus to strong light, and also to darkness? To heat 

 and also to cold? What decides whether a certain condition is " er- 

 ror" or not? A list of all the different agents that must be considered 

 " error" from the standpoint of this reaction method reveals, so far as 

 chemical or physical classification is concerned, a most heterogeneous 

 and even contradictory collection. What is the common factor which 

 makes them all error? 



Examination shows that error from the standpoint of this behavior 

 is as a rule error also from the standpoint of the general interests of 

 the organism, considering as the interests of the organism the perform- 

 ance of its normal functions, the preservation of its existence, and the 

 production of posterity. In general the organism reacts as error to 

 those things which are injurious to it, while in those conditions which 

 are beneficial it continues its normal activities. There are some excep- 

 tions to this, but in a general view it is clearly evident. There is no 

 common thread running through all the different agents which consti- 

 tute " error" in the reactions, save this one, that they are error from 

 the standpoint of the general interests of the organism. 



How can we account for the fact that these lowest organisms react 

 to all sorts of things that are injurious to them by a reaction which 

 tends to remove them from the action of the agent, by a negative reac- 

 tion? The first response to this question must be another question. 

 How can we account for the fact that in man we have the same condi- 

 tion of affairs? How does it happen that we respond by drawing back 

 both from flame and from ice, though these act physically in opposite 

 ways? Why do we seek light, but avoid a blinding glare? Why do 

 we receive without opposition certain chemical stimuli (odors and 

 tastes) and avoid others? The facts are quite parallel in man and in 

 the lowest organisms in these respects. In man certain stimuli cause 

 reactions which tend to remove the organism from the source of the 

 stimulus (negative reactions), while others have the opposite effect; 

 this is true also of Euglena and Paramecium. In both cases the stimuli 

 which produce the negative reaction form a heterogeneous collection 

 from the chemical or physical standpoint. In both cases the stimuli 

 producing the negative reaction are in general injurious to the organism. 

 The problem is one for the highest and for the lowest organisms. 



