8 THE PHILOSOPHY OF BIOLOGY 



the stimulation of our organs of sense that we are 

 sure that take place. These stimuli pass through us, 

 as it were, unless they are reflected out again as 

 actions. In this reflection, or translation of neutral 

 into muscular activity, perceptions arise. 



But even then perception need not arise. It does 

 not, as a rule, accompany the automatically per- 

 formed reflex action, because the latter is the result of 

 intra-cerebral activities that have become so habitual 

 that they proceed without friction. There are innumer- 

 able paths in the brain along which impulses from the 

 receptor organs may pass into the motor ganglia, but 

 in the habitually performed reflex actions these paths 

 have been worn smooth, so to speak. The images 

 of objects which are perceived over and over again by 

 the receptor organs glide easily through the brain and 

 as easily translate themselves into muscular, or some 

 other kind of activity. The things that matter in the 

 life of an animal which lives ' ' according to nature ' 

 are cyclically recurrent events in which, after a time, 

 there is nothing new. Most of them proceed just as 

 well in the animal deprived of its cerebral hemispheres 

 by operation as in the intact cerebrate animal. In 

 the performance of actions of this kind the organism 

 becomes very much of an automaton. 



Let something unusual happen in the street while 

 we are walking through it a runaway horse, or the 

 fall of an overhead " live " wire, for instance, something 

 that has seldom or never formed part of our experience, 

 and something that may have an immediate effect on 

 us as living organisms. Then perception arises at 

 once because the stimulation of our organs of sense 

 presents us with something which is unfamiliar, and yet 

 not so unfamiliar that it does not recall from memory, 

 or from derived experience, reminiscences of the 



