Mat 1, 1908] 



SCIENCE 



705 



■scientific procedure to manufacture or alter 

 a figrure claiming to represent the facts, in 

 order to make it agree witii a theory. My 

 figTires were made from as precise a study of 

 the facts as I could make, before I had at- 

 tempted by analysis of all the facts to seo 

 Tvhat they mean, so that the figures form 

 part of the data for my later conclusions. In 

 my preface I said that my ideal was " to 

 present an account that would include the 

 facts required for a refutation of my own 

 general views, if such refutation is possible," 

 and I should not be without the gratification 

 of having fulfilled that ideal if Torrey should 

 be adjudged to have made out his case. But 

 the reason why I held that the organism does 

 not react as directly as possible is as follows : 

 The oriented organism is swimming toward 

 the light in a spiral course, thus swerving first 

 to the right, then to the left (omitting from 

 consideration the movement in other planes). 

 ISTow the light is changed, so as to come, say, 

 from the right, as in my Fig. 95. The most 

 direct way in which the organism, swimming 

 in a spiral, could become oriented to the light 

 would be by an increase in the swerving to 

 the right and a decrease in the swerving to 

 the left, and this is what the tropism theory 

 would lead us to expect. But the fact is that 

 there is an increase in the swerving both to 

 the left and to the right, the spiral becom- 

 ing a wider one; the increase to the right 

 being, however, greater than that to the left, 

 the organism becomes gradually pointed to 

 the right. The increased swerving to the left 

 is not accounted for by the tropism theory, 

 and is indeed squarely opposed to it, while it 

 is to be expected if the analysis I gave is 

 correct. 



The point becomes quite clear when we 

 compare this reaction with that to the elec- 

 tric current, which with its undoubted local 

 action Torrey considers a typical tropism. 

 Since Euglena, itself has not been shown to 

 react to electricity, we can not make the com- 

 parison here, but Torrey does not maintain 

 his views for Euglena alone, and the facts in 

 the reactions of ciliates to light, gravity and 

 water currents are parallel to those in the 

 reactions of Euglena to light. In all these 



reactions the organism swerves, in becoming 

 oriented, only toward a certain side x, never 

 toward the opposite side y, just as in the 

 reaction of Euglena to light. But in the re- 

 action to the electric current the organism 

 may be caused by the local action to swerve 

 directly toward the side y, and to become 

 oriented in that way. Local action would 

 cause swerving toward the side y in the reac- 

 tions to light, gravity, etc., exactly as in the 

 electric current, and the fact that this does 

 not occur seems to be a demonstration that 

 local action is not the explanation in these 

 cases. 



It will then be clear, I hope, that my 

 analysis was based on a thorough considera- 

 tion of the available experimental data, and 

 not on prejudice for or against any given 

 theory. Torrey indeed admits, if I under- 

 stand him, the existence of all the factors 

 which I set forth, and the correctness of 

 my analysis so far as it deals with positive 

 factors, but believes that there is an addi- 

 tional factor, in virtue of which Euglena may 

 turn directly toward a light. Thus the 

 behavior of Euglena is more complex, accord- 

 ing to Torrey's view, than I represented it. 

 There is no doubt but that increase of knowl- 

 edge tends to reveal increased complexity in 

 the behavior of the lower organisms; of this 

 many recent examples could be given. My 

 own work has had decidedly this tendency, 

 but, as in the present case, I tried to keep the 

 theory as simple as the facts would permit. 

 But my experiments on Euglena, while not 

 revealing the power of direct turning, do not 

 disprove its existence. It has always seemed 

 as extraordinary to me as to any one else that 

 the direct turning should not occur. There 

 is little profit in discussing matters which 

 only experiment can settle. At the time my 

 work was done, I had no opportunity to study 

 the reactions of Euglena in the stage when 

 it has no fiagellum and moves by contractions. 

 Such a study is much needed, and it may 

 reveal the additional factor which Torrey 

 looks for. Many higher organisms show a 

 power of direct localization, in connection 

 with complex activities of other sorts; there 



