Mast, Loeb's Mechanistic Conception of Life. ~)Sj 



sity of the stimulating agent on the sensitive tissue and not on its 

 continuous action as Loeb's theory demands. In the rest of them 

 it has been demonstrated that stimulation of symmetrically located 

 sensitive tissue is not necessary in the process of orientation. Loeb 

 maintains (p. 220) that circus movements caused by the destruction 

 of the sensitive tissue on one side of certain animals as observed 

 by Holmes, Parker and others support his theory, but he fails 

 to consider the fact that in a number of these cases the animals 

 after some time tended to recover and orient normally with the 

 sensitive tissue functional on only one side, reactions directly in 

 opposition to his theory. In not a single case has it actually been 

 demonstrated that the response of any organism is ever in accord 

 with Loeb's theory of tropisms, with the possible exception of 

 certain reactions to electricity. This whole theory of tropisms must 

 consequently be relegated to the realm of pure speculation. How 

 then can it it be maintained that tropisms are elementary reactions 

 which have been mechanically explained? And what possible sup- 

 port can the assumption that all behavior is founded on such 

 hypothetical reactions lend to the thesis that behavior is capable 

 of mechanical explanation? 



Loeb holds that the orienting reactions in plants and animals 

 are identical, and that this supports his mechanistic ideas on behavior. 

 He says (p. 28): "In a series of experiments I have shown that 

 the heliotropic reactions of animals are identical with the heliotropic 

 reactions of plants." He brings forth several points of identity in 

 support of this contention. All of these are of essentially the 

 same nature. We shall discuss but two of them, the effect of 

 different colors and the effect of different chemicals on reactions. 



(1) "In plants", our author says, (p. 29) "only the more 

 refrangible rays from green to blue have . . . heliotropic effects, 

 while the red and yellow rays are little or less effective; and the 

 same is true for the heliotropic reactions of animals." This state- 

 ment holds, if at all, only in a very general and superficial sense. 

 The region of maximum stimulation in the solar prismatic spectrum 

 for all green plants, as far as tested, is either in the violet or the 

 indigo. Blaauw (1908) found that in the region of maximum 

 stimulation (indigo 465 /./ ; ), for oat seedlings, the efficiency on the 

 basis of equal energy is 2600 times greater than in the red, yellow 

 or green. In the unicellular and the lower multicellular animals, 

 as far as investigated, the distribution of stimulating efficiency is 

 similar to that in green plants. Engelmann gives for Ktujli'iHt, 

 blue, 470 490 /*/*, Harrington and Learning, and Mast for 

 Aincba, violet, indigo, blue; Wilson for Hydni violet, indigo, blue, 

 430490 /tjii. But in the higher animals the distribution is not in 

 agreement with this. Lubbock e. g. found the maximum for 



