Jennings, Behavior of Paramecumt. 461 



course only when it again receives water without the gas in so- 

 lution. The reaction under such conditions is a very delicate 

 one, keeping the animal in close touch with the environmental 

 conditions. The behavior does not impress one as a definite 

 "reflex"; the Paramecium is seen merely to change its course a 

 little after trying several slightly differing directions. 



The behavior of Paramecium in swinging its anterior end 

 about in a circle is essentially similar to the "feeling about, " 

 "searching," or "trial" of a higher organism. We know, of 

 course, no more of subjective qualities in any organism outside 

 the self than we do in Paramecium. If we describe the "feel- 

 ing about" or "searching" of any higher animal in a purely ob- 

 jective way, we shall find that the description takes essentially 

 the same form as for Paramecium. Under certain conditions 

 the organism performs certain movements, which subject it to 

 certain environmental changes. As long as the conditions re- 

 main of essentially the same character, it continues these move- 

 ments. As soon as these movements induce conditions differ- 

 ing in a certain way, the movements stop. This description 

 fits equally well the movements of a cat trying to escape from 

 a cage (see Thorndike, 1898), of a dog searching for a bone, 

 and of Paramecium reacting to carbon dioxide. In its method 

 the behavior seems fundamentally similar throughout. 



The behavior of Paramecia under such "repellent" stimuli 

 follows then, perhaps, as effective a general formula as could 

 be devised. When stimulated it performs movements which 

 take it away from the source of stimulus, and direct it success- 

 ively in many ways, until the stimulation ceases. Reaction of 

 this character is essentially that of "trial and error" as we find 

 it in higher animals. From this standpoint the behavior may 

 be summed up as follows: When there is "error" the organ- 

 ism "tries" various directions or methods of action till one is 

 found in which the "error" ceases. These relations have been 

 brought out by the author for lower organisms in general in a 

 previous paper (Jennings, 1904, b). 



We must ask here the question whether the reaction 

 method of Paramecium above described should or should not 



