152 THE PHILOSOPHY OF BIOLOGY 



organism ? It is true that their elements are energies 

 such as we have indicated, but these energies are 

 integrated to form individualised stimuli (Driesch). 

 The stimulus in an experimentally studied taxis is, 

 perhaps, a field of parallel pencils of light rays of 

 definite wave length ; but in the action of a man, or 

 a dog say, the stimulus is an immensely complicated 

 disturbance of the ether, producing an image upon 

 the retina of the animal. A sound stimulus employed 

 in an investigation may be the relatively simple 

 atmospheric disturbance produced by the sustained 

 note of a syren or violin-string ; but the stimulus in 

 listening to an orchestra may consist of dozens of 

 notes, with all their harmonies, sounding simultaneously 

 at the rate perhaps of some hundred or two in the 

 minute. All these are integrated by the trained listener, 

 and one or two false ones among the multitude may 

 entirely spoil the effect of the execution. Surely there 

 is here something more than a mere difference in 

 degree. 



More important still is the strict functionality 

 between stimulus and action that the theory of tactic 

 responses imposes on itself. Putting this very precisely 

 (but no more precisely than the theory demands), we 

 say that 2,A=f(x, y, z), that is, the series of actions 

 2,A (the dependent variable) is a mathematical 

 function of the independent variables x, y, z. Now is 

 there anything like this functionality between the 

 acting of the higher animal and the stimulus ? Evi- 

 dently there is not. We recognise someone whom we 

 know very well by any one of a hundred different 

 characters, mannerisms of walk, speech, dress, etc. 

 He or she is the same person, whether seen close at 

 hand, or afar off, or sideways, or in any one of almost 

 infinitely different attitudes, and we respond to each 



