May 1, 1908] 



SCIENCE 



703 



■moment. The reactions to light are bound up 

 with ahnost every possible aspect of behavior, 

 and the orientation principle plays in them 

 but a relatively small part. 



3. In Loeb's original theory nothing was 

 said as to the way in which the position of 

 orientation is reached, and I take it that he 

 does not now consider this matter as belong- 

 ing to the theory proper. But on this matter 

 a tempting idea presented itself, to the effect 

 that the position of orientation was reached 

 in the simplest possible way — by a local reac- 

 tion of the part on which the stimulating 

 agent impinges. This gave the " local action 

 theory " which made the tropism a thing of 

 such extreme simplicity; it has been applied, 

 ^ in detail or in general, to all sorts of reac- 

 tions, by many authors. While it holds in a 

 measure for the effect of the continuous elec- 

 tric current, I believe that it has been 

 •demonstrated that in the main this idea was 

 not correct; that the element it deals with 

 plays little part in behavior, aside from the 

 ■effects of electricity. With this we shall deal 

 in later paragraphs. 



Attempts have been made to controvert my 

 position on the tropism theory by the per- 

 formance of crucial experiments or by the 

 citation of specific observations. These are 

 clearly based on misunderstanding. It is 

 obvious that the relative importance of an 

 admitted single factor in producing a set of 

 complex phenomena can not be settled in this 

 manner. Valuable judgment on such a ques- 

 tion can be based only on an extended study 

 of the phenomena. My own opinion derives 

 any worth it may have solely from the fact 

 that I had worked for nine years on the 

 behavior of a large number of organisms, 

 attempting to make a careful analysis, with 

 detailed studies of the different factors in- 

 volved and the part played by each. My con- 

 clusions are of the same character as are 

 drawn from a large mass of statistical data. 

 They can be adequately controverted only by 

 showing that the analysis of this mass of 

 data, or of another equally large or larger, 



of the outward facts. The animals go toward 

 visible things that serve for food, protection, etc. 



will not yield these conclusions. Single ob- 

 servations are of course important, since they 

 are the material from which the large mass 

 is made, but single observations taken by 

 themselves do not help much in taking off the 

 fades of a long series of investigations, which 

 is what I tried to do. My conclusion, like 

 all statistical conclusions, is nothing that will 

 enable one to predict for a given individual 

 case; if it were, it would of course be of much 

 greater value than it is. No single observa- 

 tion whatever is inconsistent with my general 

 conclusion. 



Thus, writers who have flown to the defense 

 of the existence of tropisms will find them- 

 selves in no conflict with my stand on the 

 matter. It was only the prevalent opinion of 

 the wide generality and importance of the 

 phenomena that I called in question. To hear 

 that the actual existence of the tropism was 

 held to require defense came as a real surprise 

 to me. If put forward as merely one factor 

 out of many, with its relative importance sub- 

 ject to discussion, I shall agree most cordially. 



In certain quarters there seems to be an im- 

 pression that observation of the direct turning 

 of an organism toward a source of stimulation 

 is in some way opposed to my views, and that 

 citation of specific cases of this will come to 

 me as a painful surprise. Tet, of course, this 

 is one of the commonest and most evident facts 

 of behavior, and is discussed in detail in my 

 book (see, for example, pp. .306-308). Its 

 existence is required if the theory I suggested 

 is correct. I pointed out that in consequence 

 of the three factors in behavior whose impor- 

 tance I emphasized, this direct turning toward 

 a localized stimulus would occur; if it did not 

 occur, that would tend to disprove the theory. 

 " Innumerable instances of this class of reac- 

 tions could be given; they include perhaps the 

 greater number of the directed movements of 

 organisms" (p. SOY). 



Thus the direct turning of animals is not in 

 dispute. A matter that is of interest lies in 

 the answer to the question whether the turning 

 is due to the simple local reaction of the region 

 on which the stimulating agent impinges. My 

 own contention was that this is rarely the 

 case. If authors will state clearly whether 



