Significance of Tropisms for Psychology 55 



It is hardly necessary to point out here that the effects of 

 rapid changes in intensity, when they are very marked, can 

 easily complicate and entirely obscure the heliotropic phe- 

 nomena. In Hypotricha and other infusoria this differential 

 sensibility is very pronounced in response to sudden touch or 

 sudden alteration of the chemical medium, and like the tube- 

 worms they thereupon draw back very quickly. Since their 

 locomotor organs are not symmetrical, but are arranged in a 

 peculiar unsymmetrical manner, they do not, after the next 

 progressive movement, return to the former direction of move- 

 ment, but deviate sideways from it, and it is therefore easy 

 to understand that such animals do not furnish the best ma- 

 terial for demonstrating the laws of heliotropism, especially 

 since they possess only a slight photochemical sensitiveness. 

 But Jennings^ has with special preference used observations on 

 such organisms to argue against the theory of tropisms. Just 

 as the action of a constant current in muscles and nerves is 

 different from that of an intermittent current, so we find an 

 analogous case in the action of light. If we wish to trace all 

 animal reactions back to physico-chemical laws we must take 

 into consideration besides the tropisms not only the facts of the 

 differential sensibility but also all other facts which exert an 

 influence upon the reactions. The influence of that mechanism 

 which we call "associative memory" also belongs in this cate- 

 gory, but we cannot discuss this further at this place. The 

 reader is referred to my book^ as well as to the more recent 

 works of Bohn, La naissance de V intelligence^ and La nouvelle 

 psychologie animale.^ Let us bear in mind that "ideas" also 



Inst. gen. psychol., 1907; "Intervention des reactions oscillatoires dans les tro- 

 pismes," Ass. franc, d. Sciences, 1907. 



1 Jennings, The Behavior of Lower Organisms, 1906. 



2 Comparative Physiology of the Brain and Comparative Psychology, New York 

 and London, 1900. 



3 Paris, "Bibliothequedephilosophiescientifique," 1909. 



* Paris, " Bibliotheque de philosophic contemporaine," 1911. 



