268 Animal Instincts and Tropisms 



TABLE IX 



A Table Based on the Measurements of 2700 Trails Showing 



the Angular Deflections at Five Different Absolute 



Intensities 



Such constancy of quantitative results is only 

 possible where we are dealing with purely physico- 

 chemical phenomena or where life phenomena are 

 unequivocally determined by purely physicochemical 

 conditions. 



5. It seems difficult for some biologists, even with 

 the validity of the Bunsen-Roscoe law proven, to 

 imagine that the movements of the animals under the 

 influence of light are not voluntary (or not dictated by 

 the mysterious "trial and error" method of Jennings). 1 



1 According to this theory the animal is not directly oriented by the 

 outside force, e. g. the light, but selects among its random movements the 

 one which is most " suited " and keeps on moving in this direction. This 

 idea is untenable for most if not all the cases of tropisms and has been 



