vi INSTINCT 75 



has some outward effect in modifying her actions, is a 

 piece of pure anthropomorphic imagery. Upon its own 

 conditions, this argument is sound. In comparative 

 psychology the legal maxim must hold, that the thing 

 which does not at some point or other appear in action 

 must be treated as non-existent. And it may freely be 

 admitted that in many actions we ordinarily class as 

 instincts, instances of rigid adherence to type-action may be 

 found. But alongside of these, often intertwined with them 

 in the very same series of acts, will be found adaptive 

 modifications, combinations, inhibitions. Some of these 

 are sensori-motor, some of higher type, but they agree in 

 this that they are adapted to the changing and even the 

 unique and therefore they fall outside our definition of the 

 mechanical. Instincts present such modifications in very 

 various character and degree. In proportion as an instinct 

 is poor in them and therefore rigid in its execution it 

 approaches the compound reflex type, but at the limit 

 where plasticity disappears we should as a matter of 

 terminology say that the sphere of instinct is left behind 

 and reflex mechanism reigns in its stead. 



The true compound reflex is of two kinds. In the first, 

 a single stimulus sets in motion a co-ordinated series of 

 muscular contractions. Thus the contact of a foreign 

 substance with .the interior of the windpipe produces the 

 series of contractions which we call a fit of coughing. 

 Here the whole machinery must be prearranged. There 

 are in the arrangements of muscles, nerves, and nerve 

 centres certain lines of communication as complex but also 

 as definitely and rigidly fixed as those of a telephone when 

 the connection is made. The impulse having once set the 

 wave of excitement in motion, the wave travels along the 

 ordained channel till the end is reached, and organic 

 equilibrium is again restored. In the second and more 

 complex case, there is a series of stimuli as well as a series 

 of actions, the actions being so adjusted as to bring the 

 new stimuli into play. This arrangement may be wholly 

 internal, the stimuli themselves being changes within 

 the organism, as in the case of respiration. But this is 

 not essential. Under ordinary circumstances walking the 



