THEORETIC CONSIDERATIONS 369 



some way at the beginning, determining what the action 

 shall be. In this the action of living things appears to 

 contrast with that of things inorganic." 



Let us now see in how far the various theories concern- 

 ing behavior account for the phenomena set forth above. 

 The more prominent of these are those of Loeb, Jennings 

 and Driesch. We have already referred to some theories 

 elaborated to account for the reactions of plants to light 

 (see Chapter IV) . These we shall not consider again here. 



Loeb's theories refer to two features in behavior: (i) the 

 direct cause and regulation of any given reaction and (2) 

 the origin of adaptive reactions, (i) He says (1906, p. 130) 

 that the reactions " are caused by a chemical effect of 

 light " and then continues as follows, showing how the 

 reactions are regulated: "We assume . . . that if light 

 strikes the two sides of a symmetrical organism with 

 unequal intensity, the velocity or the character of the chem- 

 ical reactions in the photosensitive elements of both sides 

 of the body is different; that in consequence of this differ- 

 ence the muscles, or contractile elements, on one side of the 

 organism are in a higher state of tension than their antago- 

 nists." He claims (p. 131) that " it [is] possible by the use 

 of chemicals to control the precision and sense of the 

 heliotropic reactions " and that this and other facts prove 

 that reactions to light are caused by the chemical changes 

 produced by the light. Very few will agree that Loeb 

 has proved his point here. But practically every one 

 assumes that light does cause chemical changes in organisms 

 and that these changes affect the reactions. Many, how- 

 ever, do not agree with Loeb in the idea that they are the 

 direct and immediate cause of the reactions to light, as 

 his elucidation indicates. The fact that acids, narcotics, 

 salts, alkalis or any condition which acts as a depressant 

 may produce the same effect on the reactions of certain 

 organisms to light seems to Indicate that the reactions 

 are, at least In some Instances, due to a general effect on the 

 organism as a whole. 



