274 



MOTOR RESPONSES 



tions between these extremes. The character of the response is correlated 

 with the amount of Hght received, as well as with the rate of reception. 

 There is no fixed threshold and the "all-or-none" law does not apply 

 (Mast, 1931a). 



If an amoeba is intensely illuminated for a very short time only, move- 

 ment does not cease until some time after the light has been cut off. 

 The period between the beginning of illumination and the response is 



^ 



i 

 2 

 1 

 C 



<^ 



Figure 94. Curves showing for Amoeba proteus the 

 relation between luminous intensity, reaction time 

 (RT), stimulation period (SP) and latent period (LP), 

 and a hyperbola (H). Note that the curve for re- 

 action time simulates a hyperbola, but that the curve 

 for the stimulation period does not. This shows that 

 the amount of light energy necessary for response 

 varies with the intensity and that the Bunsen-Roscoe 

 law does not apply. (Modified after Folger, 1925.) 



K 



a-T- 



lCMINOIJs INtENSITt 



-n rr 



known as the "reaction time"; the time illumination must continue, the 

 "stimulation period"; and the time it need not continue, the "latent 

 period" (Folger, 1925). There are therefore two processes involved in 

 producing this response. The first occurs only in light, the other in light 

 or in darkness. The action of light probably results in the formation of 

 a substance which acts to produce, independent of light, another sub- 

 stance which induces the response. 



