REACTIONS OF AMEBA TO LIGHT. 69 



described, it was concluded that the nature of the stimulus which 

 enabled amebas to react to these substances at a distance also 

 remains unrecognized. Now it is possible that the nature of the 

 stimulus which makes reaction at a distance possible is the same 

 for all these various test objects, since the reactions are very 

 similar. If so, the nature of the stimulation must be simple and 

 fundamental, such as differences in electrical potential which give 

 rise to electrical currents. But if the nature of the stimulation 

 should be electiical, the quantities of current arising from the 

 various test objects must be infinitesimally small, and very great 

 if not insurmountable difficulties would be encountered in dem- 

 onstrating the presence of such small currents. 



To show the general reactions of ameba to globulin, carbon, 

 etc., when stimulated simultaneously by beams of light or of 

 darkness, the experiments may be classified as follows. 



1. Food objects (grains of globulin) were laid over a beam of 

 intense light so that the food should be very brightly illuminated 



365-372. Blue spectral light was used in the experiments 

 recorded, for blue light has been regarded as more disagreeable 

 than other spectral colors. The globulin was sensed at a distance 

 and the ameba moved toward it and ingested it. There was no 

 definite indication that the blue light had any effect in modifying 

 the behavior unless the pseudopod to the right in Fig. 368 is to 

 be regarded as expressing a deterrent effect of the light. The 

 ameba, in effect, reacted as if no spectral blue light was present. 



2. The food substance was laid some distance from the green 

 or yellow light, and in various positions with respect to the ameba 

 and the beam of light 373-437. 



(a) When the green light lay between the ameba and the 

 globulin, the light had a slight disturbing and deterring effect 

 386. The ameba made a slight detour around the green light. 

 In another test with the experiment similarly staged, the dis- 

 turbing effect of the green light was more pronounced 373. 

 The ameba made a wide detour around the light and moved into 

 contact with the globulin without coming into contact with the 

 green beam. In both experiments green light, which is positive 

 when sensed alone, became negative in contrast with the more 

 strongly (or differently) positive globulin. 



