706 



SCIENCE 



[N. S. Vol. XXVII. No. 69& 



is no antecedent improbability of tbis in 

 Euglena. 



Related to tbis matter is Torrey's discus- 

 sion of tbe question wbetber tbe organism is 

 or is not stimulated after it is oriented, wbicli 

 leads bim finally to tbe extraordinary conclu- 

 sion tbat I " insist on an interpretation of 

 organic behavior by means of general cbanges 

 in internal states tbat are psychical rather 

 than physical," and to a general condemna- 

 tion of my analysis on this account. Most 

 of tbe points made in Dr. Torrey's interest- 

 ing paper I can appreciate, but at the dis- 

 cussion -which leads to this conclusion regard- 

 ing psychic factors I must confess my 

 astonishment. The conclusion is reached 

 only by the aid of the somewhat desperate 

 assertion that to say tbat an oriented organ- 

 ism is subjected to no general stimulation 

 " is no more than saying it then possesses no 

 feeling of discomfort." Had I made such a 

 statement, I should have expected much just 

 and severe criticism for " psychologizing " ; 

 for " crude anthropomorphism." 



The root of the difficulty lies in a misunder- 

 standing of certain of my attempts to avoid 

 the use of indefinite terms not having a pre- 

 cise experimental meaning; it comes finally 

 to a simple matter of definition. Experi- 

 mentally, it has seemed to me that the study 

 of behavior reduces mainly to a study of two 

 things: (1) the causes of changes in behavior; 

 (2) the nature of the changes themselves. 

 Now these two things correspond nearly to 

 ■what are commonly called stimuli and reac- 

 tions, though tbe common usage is a little 

 less precise, not always representing experi- 

 mental concepts. I, therefore, adopted for ex- 

 perimental discussions tbe word reaction as 

 signifying a change in 'behavior; tbe word 

 stimulus as meaning tbe cause of a change in 

 behavior, though so far as I could I used the 

 plain phrases in place of the two terms. 

 Unless some such definitions are used there 

 is no experimental method of telling whether 

 an organism is reacting or not; whether it is 

 stimulated or not. On page 283 of my book 

 I took tbe greatest pains to emphasize the 

 fact that my discussion would not be intel- 

 ligible unless this meaning of the word reac- 



tion were kept in mind. With this, a stim- 

 ulus, as the cause of a reaction, is likewise 

 clearly defined; tbis definition I had already 

 given on page 6. 



Stimulation and reaction are evidently, as 

 thus used, correlative terms ; if there is no 

 reaction, there is no stimulation. I have no 

 desire to insist that these are the only pos- 

 sible definitions; I merely wish to point out 

 that this was my explicitly declared usage. 

 Now, if we apply these definitions, the whole 

 structure of difficulties raised by Torrey fall& 

 to the ground. From the definitions it fol- 

 lows tbat when the movements of an organism 

 are uniform, it is not stimulated. After the 

 infusorian has become oriented to light, it does 

 not change its movements, but swims in the 

 same way it did before; there is then no ex- 

 ternal evidence that it is stimulated, and if 

 my purely empirical definition is accepted, it 

 is not stimulated. 



If it be maintained, as Torrey does, that 

 the organism is nevertheless stimulated at 

 such a time, then evidently some internal con- 

 dition is talien as a criterion of stimulation. 

 Tbis is precisely the criterion which Torrey 

 incorrectly attributed to me, and on the 

 ground of which he charged me with making 

 " feelings of discomfort " and other psychical 

 phenomena the basis of my analysis. If there 

 were any sound foundation for his argument, 

 I could retort tbat it is bis view that calls 

 for the psychical factors. But, of course, 

 there is no reason for dragging in psychic 

 factors at all; it is perfectly easy to suppose 

 that the organism when oriented is in a dif- 

 fering physico-chemical state, and this as- 

 sumed state might be considered stimulation, 

 unless the empirical definition of stimulation 

 as correlative with reaction is preferred. To 

 be unable to conceive a change in physio- 

 logical state otherwise than as psychical 

 would seem to unfit one completely for the 

 objective analysis of behavior; such changes 

 demonstrably occur even in unicellular organ- 

 isms. 



It is evident that the highly objectionable 

 propositions which Torrey deduces from my 

 discussion, to the effect that there can not 

 be " a constant stimulus that does not induce 



