328 LIGHT AND THE BEHAVIOR OF ORGANISMS 



It is claimed that a sudden increase of intensity causes 

 an immediate cessation of movement either in white Hght 

 or in light containing only the shorter waves, but that 

 " after a few minutes [exposure] streaming will commence 

 under any light if the amoeba be a fairly active individual" 

 (p. 1 6). The authors appear to think that some colors 

 actually cause an increase in the rate of movement in the 

 amoebae: " That red is the most powerful excitant to flow 

 is indicated by the shorter latent period after quiescence 

 in white light." There is however little evidence sup- 

 porting this conclusion. 



Harrington and Leaming did not ascertain the intensity 

 of light transmitted by the different filters, and the light 

 was not spectroscopically examined, so that the purity of 

 the colors used remains unknown. Similar results were 

 however obtained in spectral colors, but the authors un- 

 fortunately have not described how the spectrum was 

 produced or what kind of light was used as a source. 

 Their results have occasionally been seriously questioned. 



5. Original Observations on Amoeba 



Owing to the questionable character of some of the 

 results of Harrington and Leaming and to the fact that 

 the region in the spectrum of maximum effect on the 

 movement could not be definitely located from their data, 

 it seemed desirable to have the experiments repeated. 



a. Experiments with color filters. — Early in June, 

 1909, Dr. H. S. Jennings put at my disposal an excellent 

 culture of Amoeba proteus, which had come up in hay 

 infusion used in rearing Paramecia. Specimens of this 

 culture were studied both in a solar prismatic spectrum 

 and in different colors produced by means of filters which 

 were kindly furnished by Dr. R. P. Cowles. The filters 

 were prepared and spectroscopically tested in the physical 

 laboratory of Johns Hopkins University. The red was 

 transparent from 620^^ out, opaque from 450 to 590^^" and 



