376 MARGARET FLOY WASHBURN 



into a region cither too light or too dark for its existing state 

 of adaptation ; the reflexes cease when the light is diffused. 

 Foul water makes all the individuals positive ; movement from 

 darkness into the open would be their flight-reflex under normal 

 conditions. 



I less also, as is well known, opposes the identification of pho- 

 totropism in animals and in plants, although on other grounds. 

 He here (41) reports, besides experiments on fish and birds, some 

 tests made with the branchiopod Artcmia salina, which is nor- 

 mally strongly negative in its response to light. He put a num- 

 ber of individuals into a cubical vessel placed at the middle of 

 a black tunnel ; at either end of the tunnel was a light. The 

 sensitiveness of the animals to differences in the intensity of 

 these two lights was measured by keeping one of them at a 

 constant distance of thirty centimeters, and moving the other 

 one. No difference in the behavior of the Artemias was observed 

 until the second light was moved either further, off than thirty- 

 two centimeters or nearer than twenty-nine centimeters. When 

 a red light and a blue light were used, a very light red and a 

 very dark blue proved to be equal in their effect on the light 

 reactions of the animals, and corresponding results were ob- 

 tained by equating red and blue with white light. Another 

 method was used to investigate the reactions of Artemia to 

 colored light. The cubical vessel containing the animals w T as 

 divided by glass partitions into four parallel compartments, and 

 a spectrum thrown through the side wall in such a way that 

 one compartment was illuminated chiefly by red light, one by 

 orange and yellow, a third by yellow-green and green, and the 

 fourth by blue and violet. The Artemias all crowded against 

 the opposite wall of the vessel. A long, cylindrical incandescent 

 tube was placed parallel to this other side, and the intensity was 

 measured of its light when it was able to overcome the negative 

 effect of the colored light in each compartment. The brightness 

 values of the colors thus measured indicated that they were the 

 same as those for a color-blind human being. Hess believes 

 that he has found the brightness values of colors to the verte- 

 brate eye, on the other hand, to be identical with those for the 

 normal human eye, and argues on this ground against Loeb's 

 position that the effect of light on animals and on plants is 



