Vol. LIU 



December, 



No. 6 



BIOLOGICAL BULLETIN 



THE RELATION BETWEEN THE RESPONSES BY 



AMCEBA TO MECHANICAL SHOCK AND TO 



SUDDEN ILLUMINATION. 1 



HARRY THOMAS FOLGER (1889), 

 UNIVERSITY OF MICHIGAN, ANN ARBOR, MICHIGAN. 



The reactions induced in Amoeba by mechanical shock are re- 

 markably like those brought about by sudden illumination ( Folger, 

 '25, '26). In both cases the response consists of a cessation of 

 movement, the animal remaining- inactive for a short time, then 

 resuming locomotion. In both cases a short period intervenes be- 

 tween the application of the stimulus and the response, and this 

 period, the reaction-time, varies directly with the magnitude of 

 the stimulation, becoming shorter as the latter increases ; while 

 the time during which the amoeba is inactive, the period of qui- 

 escence, likewise dependent on the magnitude of the stimulus, be- 

 comes longer with increase of the latter. Moreover, in both in- 

 stances a certain amount of time must elapse after a stimulus has 

 been applied before the amoeba will respond to a second stimulus. 

 Thus, an exposure to light of sufficient duration to bring about a 

 response must be followed by an absence of light or at least by a 

 lowered intensity for a certain amount of time before the amoeba 

 will again respond to an increase in illumination. This occur- 

 rence of a period during which the amoeba is apparently revert- 

 ing to the condition it was in before stimulation, which I have 

 called the period of recovery, 2 and the fact that a recovery occurs 



1 Contribution from the Zoological Laboratory of the University of 

 Michigan. 



2 The term recovery has been used here simply because it is descriptive ; 

 refractory period has been employed and in the case of light dark adaptation. 

 Recovery should not be confused with the resumption of protoplasmic flow 

 by the amoeba. The animal may have resumed locomotion and be moving 



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