i MENTAL EVOLUTION 5 



cones of the retina produce in their cells some physical 

 change. It is known that the change propagates a disturb- 

 ance along the fibres of the optic nerve and that this dis- 

 turbance proceeds at a measurable speed in the form of a 

 wave and is accompanied by certain electrical phenomena. 

 The result of this disturbance, to omit the intervening 

 stages, is to set up certain chemical changes in the muscle- 

 cells which move the eyelids, causing them to thicken and 

 shorten and thereby to draw down the lids. In the case 

 of the tears the disturbance is communicated to the cells 

 of a gland which it causes, instead of contracting, to secrete 

 their peculiar product. 



2. In all this there nowhere appears any reason to im- 

 pute the existence of any forces but those that we call 

 mechanical or chemical. It is true that the details of the 

 mechanism or of the chemical change are not yet fully 

 made out. But so far as investigation has gone it has 

 yielded no reason for excepting reflex-phenomena from 

 ordinary mechanical laws. The reaction is no doubt com- 

 plex, but it is pretty nearly as regular and undeviating as 

 the response of any confessed machine to the pressure of 

 a knob or the turning of a handle. The child squeezes its 

 doll and in virtue of a cunningly concealed mechanism it 

 cries. Something squeezes the child and in virtue of a 

 still more cunning mechanism it cries more effectually. 

 There is the mechanical view. And at least in the case of 

 blinking it has this to support it that the response as a 

 rule is given unconsciously and intelligence neither makes 

 nor meddles with it. The act serves a purpose yet it is 

 not purposive. It is the result of a preordained structure, 

 of a structure which has come into existence to do that 

 particular thing quite as much as a bit of machinery has 

 been made to play its particular part whatever it be. It 

 is a case of a function executed by the organism and 

 serving the ends of the organism, which depends never- 

 theless on purely physical laws and in which conscious 

 purpose has no part to play. 



The higher and more complex acts of animals and of 

 man differ, it would be admitted, in important respects 

 from responses of this type. They are not unattended by 



