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SCIENCE 



[N. S. Vol. XXVII. No. 



action; it is merely a charaeterization of cer- 

 tain ways in wiiicli such action occurs. Some 

 of the relations brought about in such action 

 are lasting, while others are fleeting; those 

 which last are said to be " selected." The 

 study of selection is an examination of the 

 relative permanency of different physico- 

 chemical and physiological relations, and it 

 is eminently a matter for experimentation. 



Again, in addition to the rapid processes 

 occurring mainly in the lifetime of individ- 

 uals, there are slow processes requiring more 

 than a generation to produce evident effects; 

 various aspects of these we call "heredity," 

 "evolution," "genetics," etc. These slow 

 processes belong as much to physiology as do 

 the rapid ones. The existing condition of 

 living things is known to be largely a product 

 of these processes, so that to attempt to ex- 

 clude them from consideration and to act as 

 if their effects did not exist, when we are 

 trying to understand living things, is a most 

 futile proceeding. These matters are coming 

 rapidly under experimental study, so that at- 

 tempts to exclude them from consideration in 

 physiology, as "historical," can not endure 

 much longer. 



We now come to the matter which seems to 

 underlie most of the criticisms of my discus- 

 sion. Certain authors seem to identify the 

 "tropism theory" with the view that the be- 

 havior of organisms is to be explained by 

 objective, experimentally determinable factors. 

 They feel that an attack on the " tropism the- 

 ory" is an attack on this view; this comes 

 forth notably in the criticisms made by Loeb 

 and Torrey, and it is evident in the attitude 

 of some other writers. 



There is, so far as I can see, nothing in the 

 facts and relations which I have brought out 

 that in any way opposes the principle that 

 behavior is to be explained by objective, ex- 

 perimentally determinable factors — or indeed 

 that bears in any way on the question. I have 

 simply assumed throughout that it is to be 

 explained in that way, and I do not see how 

 experimental investigations can proceed on 

 any other basis. Beginning my work in 1896, 

 when the movement led by Loeb against the 



use of psychic concepts in explaining ob- 

 jective phenomena was in full swing, I con- 

 sidered that battle as fought and won; I have, 

 therefore, ever since proceeded, without' dis- 

 cussion or ado of any sort, on that basis. 

 Every one must recognize the tremendous 

 service done by Loeb in championing through 

 thick and thin the necessity for the use of 

 objective, experimental factors in the analysis 

 of behavior. No convinced experimentalist, 

 knowing the previous history of the subject, 

 can reread, as I have just done, Loeb's early 

 work on behavior without being filled with 

 admiration for the clear-cut enunciation, de- 

 fense and application of the principles on 

 which valuable experimental work has rested 

 since that time, and on which it must continue 

 to rest. 



Any differences of opinion between Loeb 

 and myself are then matters of detail; they 

 concern merely the results of the application 

 of the agreed principles of investigation. It 

 has seemed to me that some of the experi- 

 mentalists have rested content with superficial 

 explanations; that they did not realize the 

 complexity of the problems with which they 

 were dealing. This has been the history of 

 most applications of experiment to biology; 

 the more thorough the work, the deeper are 

 the problems seen to be. 



Thus I have not hesitated to bring forth 

 facts tending to show the inadequacy of the 

 physico-chemical factors thus far set forth, 

 and doubtless some have suspected that this 

 was done with the concealed purpose of dis- 

 crediting the general adequacy of such factors. 

 This is a complete mistake; I did not till 

 lately realize even the existence of such a 

 suspicion. Complete confidence in the experi- 

 mental method removes anxiety as to the effect 

 of criticizing the details of its application. 

 My objections are only to the adequacy of 

 particular factors; they are based on experi- 

 mental grounds, and the difficulties they raise 

 are to be resolved only by experimental study. 

 There is a vast difference between holding 

 that behavior is fundamentally explicable on 

 experimental grounds, and holding that we 

 have already so explained it. 



