REGULATION OF REACTIONS 29 1 



August 23, 1904, was a bright, clear day. At 4 p.m. 

 specimens were collected in a place which had been well 

 exposed to the sun much of the afternoon. Soon after 

 reaching the laboratory, these specimens were found to be 

 positive in light intensities varying from 230 to 1400 ca. m. 

 The colonies not used in these tests were put into a liter 

 jar and placed in strong diffuse sunlight in a west window. 

 Here many of the colonies soon aggregated on the side of 

 the jar farthest from the source of light. At 5.45 p.m., 

 after having been in the window about an hour, they were 

 found to be negative to an intensity of 230 ca. m. and at 

 6.45 P.M. to an intensity as low as 3 ca. m. They seemed 

 to become more strongly negative the longer they were left 

 in the window, although the light from 6.30 P.M. on was 

 quite dim. At the close of the experiment, 7 p.m., certain 

 colonies which had been strongly negative to an intensity 

 of 230 ca. m. were found to be positive to an intensity 

 of 400 ca. m. The following day these organisms were 

 exposed again to light of 1400 ca. m. and to various 

 lower intensities, but there were no indications of negative 

 reactions. 



In certain cultures of attached specimens of . Stentor 

 coeruleus kept in low light intensity I have seen some 

 specimens respond definitely by violent contraction to a 

 sudden increase of illumination of even less than 120 ca. m., 

 while other specimens in the same culture did not re- 

 spond at all, even to a much greater increase. In other 

 cultures under the same environmental conditions none 

 of the specimens could be made to respond even by flash- 

 ing the most intense direct sunlight (5000 ± ca. m.) upon 

 them. 



Free-swimming individuals at times avoid even the 

 faintest illumination, while at other times they are found 

 in strong, diffuse daylight. These creatures apparently 

 become accustomed to light very readily. They were 

 often observed to give very definite responses In diffuse 

 light when first taken from a culture jar, and none at all 



