172 Journal of Comparative Neurology and Psychology. 



taken in connection with the surface tension of the fluids, but this ex- 

 planation fails when we consider the formation of free pseudopodia, 

 and (lit^cover that all the processes concerned in locomotion can take 

 place without adhesion to the substratum." 225. 



Seventh Paper. The Method op Trial and Error in the Behavior 

 OF Lower Organisms. 



In higher animals we speak of karm'ng hy the method of trial and 

 error, and in unicellular organisms we may speak of the trial and error 

 method of reaction. In the former instance the animal when first 

 confronted by a certain situation exhibits a number of reactions ; one 

 of these reactions brings satisfaction and therewith the trial reactions 

 cease. The next time the same situation is presented the animal, if it 

 has learned, omits the useless or harmful trials and performs only the 

 appropriate reaction. In the latter instance, namely, in case of uni- 

 cellular organisms, each re-presentation of the situation brings about, 

 so far as yet observed, the same sort of trial and error series of reac- 

 tions. Whereas the mammals after a number of experiences omit the 

 majority of the trials, the protozoa apparently have to go through the 

 whole gamut of tests each time. 



Trial may then be defined as the process of testing different por- 

 tions of the environment, and error is descriptive of those trials which 

 result in negative reaction. Now, the problem proposed by the au- 

 thor is, How is error distinguished by the organism? "In ourselves the 

 stimuli which induce the negative reaction bring about the subjective 

 state known as pain, and popularly we consider that the drawing back 

 is due to pain. Is there ground for this view?" p. 248. This prob- 

 lem, Jennings insists, is one throughout the animal series. 



Finally, the method of trial and error which the author be- 

 lieves to be the prevalent mode of reaction among lower organisms is 

 not in agreement with the principles of reaction which are at the bot- 

 tom of the tropism schema. For the tropism is a fixed way of react- 

 ing in response to a certain stimulus, and it has no place for the trials 

 which have been demonstrated to occur. 



Whether this is fair to the advocates of the tropism formulae for 

 reactions would be hard to say. Certainly some of them will at once 

 contend that Jennings by merely breaking up the stereotyped reaction 

 into a number of parts has not altered the nature of the reaction. 



The author's insistance throughout this volume upon the import- 

 ance of internal conditions in lower organisms is certainly justified by 

 the facts he presents. 



