154 THE PHILOSOPHY OF BIOLOGY 



it should do on a purely mechanistic hypothesis of 

 action, but to the typical wholes which are expressed 

 in these groupings. 1 



It is no answer to this argument to say that it is 

 not the actual atmospheric vibrations (in the case of 

 the conversation), nor the optical image (in the case 

 of the recognition of a friend), which are the true 

 stimuli, but rather the mental conditions, or states of 

 consciousness, aroused by these physical agencies. If 

 we are to adopt a strictly mechanistic method of ex- 

 plaining actions, such a method as that indicated by 

 Loeb's hypothesis of the purely tactic behaviour of 

 his caterpillars, then these atmospheric vibrations 

 and optical images are most undoubtedly the true 

 stimuli, and the reactions must be functions of them 

 in the mathematical sense. But since this strict 

 functionality does not exist in any behaviour-reaction 

 closely analysed, we must grant at once that it is, 

 indeed, not the physical series of events that deter- 

 mines the actual response, but truly the conscious 

 state immediately succeeding to these physical sense- 

 impressions. Now let us see to what conclusions this 

 admission leads us. 



Between the external stimulus (the atmospheric 

 undulations impinging on the auditory membranes, 

 or the light radiations impinging on the retinae) and 

 the behaviour-reaction something intervenes. This is 

 the individual history of the organism, the " associa- 

 tive memory ' of Jacques Loeb, the ' physiological 

 state " of Jennings, the " historical basis of reacting ' 

 (historische Reaktionsbasis) of Driesch, or the " dura- 

 tion " of Bergson. The last concept is the most subtle 



1 Thus to the ordinary woman the sight of a cow in the middle of a country 

 road produces a certain definite feeling of apprehension, which is always the 

 same although the optical image of the animal differs remarkably in different 

 adventures. 



