Introductory Remarks ii 



a guide wherever we attempt to put science beyond the 

 possibiHty of mysticism. As soon as we can show that 

 a hfe phenomenon obeys a simple physical law there 

 is no longer any need for assuming the action of non- 

 physical agencies. We shall see that this has been 

 accomplished for one group of animal instincts ; namely 

 those which determine the relation of animals to light, 

 since these are being gradually reduced to the law of 

 Bunsen and Roscoe. This law states that the chemical 

 effect of light equals the product of intensity into dura- 

 tion of illumination. Some authors object to the 

 tendency toward reducing everything in biology to 

 mathematical laws or figures; but where would the 

 theory of heredity be without figures? Figures have 

 been responsible for showing that the laws of chance 

 and not of design rule in heredity. Biology will be 

 scientific only to the extent that it succeeds in reducing 

 life phenomena to quantitative laws. 



Those familiar with the theories of evolution know 

 the extensive role ascribed to the adaptations of organ- 

 isms. The writer in 1889 called attention to the fact 

 that reactions to light — e. g., positive hehotropism — 

 are found in organisms that never by any chance make 

 use of them; and later that a great many organisms 

 show definite instinctive reactions towards a galvanic 

 current — galvanotropism — although no organism has 

 ever had or ever will have a chance to be exposed to 

 such a current except in laboratory experiments. This 



