RESPONSES BY AMCEBA. 



409 



posure to light. Individual No. 2 reacted 5 times out of 6 trials 

 when subjected to mechanical shock alone, and only 4 times out 

 of 8 trials when the mechanical shock was preceded by illumina- 

 tion. Altogether, the 4 animals used in the experiment responded 

 to mechanical shock 19 times out of 21 trials when this stimulus 

 did not follow an exposure to light, while they failed to respond 

 to it 16 times out of 26 trials when it did follow illumination, thus 

 indicating that exposure to light does influence the response to 

 mechanical shock. Even more convincing, however, are the re- 

 sults of an experiment to be described in the next paragraph. 



It has already been shown (Folger, '26) that the length of time 

 that an amoeba remains inactive after stimulation by a mechanical 

 shock is markedly affected by the length of time that has elapsed 

 since a previous mechanical shock, and that, within limits, this 

 quiescent period increases with increase in the length of time since 

 the previous stimulation. Thus, the period of quiescence result- 

 ing from a mechanical shock which follows 30 seconds after a 

 preceding similar shock is not likely to be nearly so long as that 

 brought about by a shock following after an interval of 60 seconds. 

 Table III. records an experiment in which somewhat similar re- 



TABLE III. 

 SHOWING THE EFFECT OF LIGHT ON MECHANICAL SHOCK. 



In each test the amoeba was first exposed to light and then allowed to re- 

 cover from the effects of this stimulus for the time indicated in the table, 

 after which it was subjected to a mechanical shock. The period of qui- 

 escence, recorded in the last column, consists of the time during which the 

 amoeba was inactive after it had been subjected to a mechanical shock. 



suits were obtained, but in which the organism was first stimulated 

 by light and then by mechanical shock. From the table it is seen 

 that the amoeba reacted only twice out of 4 trials when 15 seconds 

 were allowed for recovery between stimulation by light and by 



