218 JACQUES LOEB AND HARDOLPH WASTENEYS 



darkness to light gather under the red ; and animals which prefer 

 light to darkness gather under the blue glass. This led him to 

 enunciate the law that animals which are 'fond' of light are also 

 'fond' of the blue; and animals which are 'fond' of the darkness 

 are also 'fond' of the red. We see again the tacit assumption 

 that animals which collect under blue glass do so because they 

 are 'fond' of this type of light, while animals which collect under 

 the red light do so because they are 'fond' of this type of light. 



The field of animal reactions received a different interpretation 

 by Loeb/ who showed that these results can be explained on a 

 purely objective basis without our ascribing to lower organisms 

 sensations the existence of which we can neither prove nor 

 disprove. Loeb showed that the phenomena observed by Bert, 

 Graber, and others can be explained on the assumption that the 

 light automatically orients the animals or determines the direction 

 in which they move, there being two classes of animals, one 

 class being automatically compelled to move to the source of 

 light, the other being compelled to move in the reverse direc- 

 tion; and he pointed out that this phenomenon is the same as 

 the heliotropic reaction in plants, the stem of plants bending to 

 the source of light, the roots bending away from it ; or the swarm- 

 spores of algae moving to or from the light. Accordingly he 

 designated the animals going to the light as positively heliotropic, 

 those going away from the light as negatively heliotropic. 



As this bending effect in the plant is a purely automatic orien- 

 tation of the plant, brought about through the influence of the 

 light, so in the animals we are, according to Loeb's theor}^, deal- 

 ing only with an orienting effect of the light for the explana- 

 tion of which merely physicochemical conditions are adequate; 

 without our being compelled to introduce hypothetical sensations 

 as a necessary link in the mechanism. This purely mechanistic 

 conception of the motions of animals to or from the light has 

 recently received a new support by the invention of heliotropic 

 machines by Mr. John Hays Hammond, Jr., in which the two 



* Loeb, J. Der Heliotropismus der Tiere unci seine Uebereinstimmung mit 

 dem Heliotropismus dcrPflanzen. Wiirzburg, 1890. Sitzungsber. d. Wiirzburger 

 physikal-mcd. Oospllsch., Jan. ISSS. 



