iv REFLEX ACTION 45 



5. So far we have found nothing to differentiate the 

 reflex mechanism from any other piece of machinery. 

 There is a certain arrangement a sense-organ, an afferent 

 nerve, a nerve centre consisting essentially of a more or less 

 complicated ramification of nerve fibres, one or more 

 efferent or motor nerves, and one or more muscles. Apply 

 a stimulus, and the machinery works. Nerves, nerve 

 centres, and muscles are thrown into activity. As in a 

 machine the parts not merely act, but act together in a 

 prearranged harmony, the general tendency of which is to 

 deal with the stimulus in the way best suited to the needs 

 of the organism. 



These last words recall us once more to the conception of 

 purpose, and we may now put the question thus. Is it 

 the needs of the organism that determine the action, or is 

 it the preformed structure ? Is the act the result of a struc- 

 ture that is already there, or is it adopted as a means to an 

 end, which is still to be realised ? Broadly speaking the 

 facts leave us in no doubt as to the answer. In the typical 

 reflex the structure is " already there." The organism or 

 part of it is attuned to a certain kind of stimulus so as to 

 react to it in a special manner. It is so attuned that the 

 manner of reaction adopted for each stimulus is under 

 ordinary circumstances beneficial to the organism. Of the 

 structure we may perhaps say with certain reservations 

 that it has grown up because it is useful to the organism. 

 But of the particular act we must say that it is performed 

 not because it is useful at the present moment, but because 

 it is the necessary result of the action of a given stimulus 

 upon a given structure. Circumstances may be such that 

 this response does not serve the normal " purpose," but 

 unless these " circumstances" are counter stimuli acting on 

 the nerve centres, they have no effect. Taking this last 

 qualification into account, we may say that a reflex action 

 is a response to the present operative stimuli as such. 

 This differentiates it from an act of purpose. Purposive 

 action may also from one point of view be regarded as the 

 response of a structure to its surroundings in accordance 

 with laws which are uniform after their kind. But here 

 the fundamental law is precisely that action is determined 



