56 The Animal Mind 



> Is there any evidence of the presence in Paramecium of 

 JL&ie revival of past experiences in any form ? The answer to 

 \this question must be negative, as in the case of Amoeba. 

 Immediately preceding stimulation does have some effect 

 upon the response to present stimulation, but these effects 

 are all of such a character as to suggest rather the disap- 

 pearance of possible consciousness than the recall of a memory 

 image. Jennings mentions several instances. "If a Para- 

 mecium is subjected to a strong induction shock, it fails for 

 some time thereafter to react to weak shocks, though at the 

 beginning it reacted to these" (211, p. 100). Such a result 

 is due probably to fatigue. "Paramecia which have been 

 living at the usual temperatures show a temperature opti- 

 mum of about 24 to 28 degrees ; if they are kept for some 

 hours at a temperature from 36 to 38 degrees, the optimum 

 rises to 30 or 32 degrees. A change in the individuals in- 

 duced in this way is commonly spoken of as acclimatiza- 

 tion " (211, p. 101). Further, "if a bit of filter paper is placed 

 in a preparation of Paramecia, the following behavior may 

 often be observed. An individual swims against it, gives the 

 avoiding reaction in a slightly marked way, swimming back- 

 ward a little; then it swims forward again, jerks back a 

 shorter distance, then settles against the paper and remains. 

 After remaining a few seconds, it may move to another 

 position, still remaining in contact with the paper. Then it 

 may leave the paper and go on its way "(211, p. 101). Be- 

 havior of this type, where a stimulus at first occasions the 

 negative reaction, but on immediate repetition ceases to do 

 so, we shall find very common among the lower forms of 

 animals; it suggests simply that the stimulus acts less and 

 less strongly on repetition, not that the effects of its earlier 

 application are consciously recalled. 



Jennings's work on other ciliate Protozoa, as well as on the 



