346 LIGHT AND THE BEHAVIOR OF ORGANISMS 



color and that the reactions are controlled by subjective 

 sensation, are evidently without experimental foundation. 

 They are reached purely through human analogies. 



6. LoeVs Observations 



The accounts of Loeb's experiments on the effect of 

 different colors on reactions are found in two papers, 

 published in 1890 and 1893 respectively. Of the two 

 colors, red and blue, used in these experiments, the former 

 was produced by means of a solution of potassium bichro- 

 mate or ruby glass, and the latter by means of " cobalt 

 glass or an ammoniacal solution of copper." In each of 

 these two colors the reactions of the following animals 

 were studied: Musca larvae, plant lice, caterpillars of 

 Porthesia chrysorrhoea, moths of Sphinx euphorbia and 

 Geometra piniaria, various copepods, the meal worm Tene- 

 brlo molitor, and larvae of the June bug Melolontha vul- 

 garis, Limulus polyphemus, and Polygordius. 



Loeb maintains that these forms react in blue light 

 essentially as they do in white; that the negative forms are 

 negative in the blue light and the positive forms positive; 

 and that the red rays have a slight effect on the move- 

 ment of some of the animals but none on that of others. 

 He concludes that in all of these animals " the more 

 strongly refrangible rays of the visible spectrum are the 

 most active heliotropically, as in the case of plants " 

 (1905, p. 294). He also says (1905, p. 73), " I have con- 

 firmed the identity of animal with plant heliotropism on 

 crabs (Gammarus locusta, Cuma Rathkii), naked snails 

 and worms (leeches, planarians, earth-worms and others)," 

 but he does not state definitely that he studied the reac- 

 tions of these forms in colored light. 



In harmony with the results of Graber's experiments, as 

 well as with those of various other investigators, Loeb's 

 results show fairly clearly that blue is more efficient than 

 red in stimulating the organisms he tested, but they do 



