September 6, 1907] 



SCIENCE 



319 



a point midway between two lights of equal 

 intensity that are equidistant from the organ- 

 ism itself, it does so, he believes, because in 

 such an orientation it is subjected to no gen- 

 eral stimulation, which is no more than saying 

 it then possesses no feeling of discomfort. In 

 the face of the facts which have been pre- 

 sented to show that light induces definite reac- 

 tions of definite muscles, just as definite as 

 the complex but unconscious reactions of a 

 decapitated frog to, let us say, acetic acid 

 applied to the skin of its back, he insists upon 

 an interpretation of organic behavior by 

 means of general changes in internal states 

 that are psychical rather than physiological. 

 Here, as it seems to me, he has abandoned 

 one attempt at explanation for an alleged ex- 

 planation which itself assumes the facts most 

 in need of elucidation. 



It will not be necessary to delay further by 

 examining the phenomena of geotropism. Or- 

 ganisms respond to the stimulus of gravity by 

 reactions essentially similar to those which 

 characterize their reactions to light. No new 

 elements are introduced. It may be well, 

 however, to summarize the discussion up to 

 this point before entering upon a somewhat 

 different line of criticism. 



Jennings has applied to the facts of be- 

 havior a general explanation in the form of 

 two principles. According to these principles, 

 no definitely directive or fixed reactions, such 

 as reflexes', tropisms, habits and instincts are 

 primary, but result from the selection from 

 random movements of such as are advantage- 

 ous to the organism, and the gradual develop- 

 ment of these advantageous reactions in the 

 individual by the law of the readier resolution 

 of physiological states, in the race by the 

 operation of organic selection. The primary 

 type of reaction is non-directive, and is illus- 

 trated by some such response as the motor 

 reaction of Paramecium. The necessary con- 

 dition of stimulation is an abrupt change in 

 the environment, which leads to a general re- 

 action of the whole organism. What the ad- 

 herents of the tropism theory call a condition 

 of symmetrical stimulation is, therefore, in 

 reality a condition of no stimulation at all. 



The existence of constantly acting directive 

 stimuli after orientation is explicitly denied. 

 In our examination of this general view and 

 the propositions on which it is based, we have 

 arrived at the following preliminary conclu- 

 sions : 



I. That the essential facts of galvanic stim- 

 ulation are identical in widely different or- 

 ganisms, which suggests their fundamental 

 character; that there exist among the phe- 

 nomena of galvanic stimulation two types of 

 reaction, (1) non-directive, dependent on sud- 

 den changes of current potential, and (2) 

 directive, dependent upon the action of a 

 constant current which, it was shown, pro- 

 duces, after orientation an observable effect 

 on locomotion; further, that the very fact of 

 the pronounced absence of galvanic stimuli 

 in nature greatly increases the value of gal- 

 vanic stimulation as an aid to analysis. 



II. That organisms exhibit toward light 

 (gravity as well) two types of reaction com- 

 parable with those typical of galvanic stimu- 

 lation; that certain responses, in Euglena and 

 Anurcea, which are readily analyzed on the 

 basis of these two kinds of stimulation, afford 

 no support for the trial and error schema; 

 that in heliotropism as well as in galvano- 

 tropism, the oriented organism is in a condi- 

 tion of physiological stimulation, and that the 

 response to stimulation is local; finally, that 

 the interpretation of the behavior of helio- 

 tropic organisms on the basis of general 

 changes concerning the whole organism, not 

 only does not accord with the known facts, but 

 is rather psychical than physiological in char- 

 acter. 



If these conclusions be sound, it follows 

 that the method of trial, however useful it 

 may be in the interpretation of certain classes 

 of facts relative to the behavior of organisms, 

 lends no aid toward the analysis of certain 

 other classes of facts in the same field; that 

 it not only does not simplify the general prob- 

 lem which these facts present; but that it ac- 

 tually tends to divert inquiry from a line of 

 investigation which has been shown by recent 

 achievements to be not only promising but 

 fertile. 



