38 THE PHILOSOPHY OF BIOLOGY 



carried out, becomes a " motor habit " or the basis of 

 a reflex, or in some other way, as in the process of 

 immunisation, remains a part of the modes of function- 

 ing of the animal. In our behaviour certain cerebral 

 nerve tracts become laid down and continue to exist 

 throughout life, modifying all our future experience. 

 Our past experience accumulates. There must be 

 direct continuity in our flux of consciousness, for no 

 perception seem.s ever to fade absolutely from memory. 

 This continual addition of perceptions to those that 

 already exist makes our consciousness ever become 

 more complex, so that a perception experienced for 

 the first time is never quite the same when it is again 

 experienced. The first time that we go up and down 

 in an elevator, or sit on a " joy-wheel," or ascend in a 

 balloon or an aeroplane, or become intoxicated, con- 

 stitutes an unique event in our lives, and we experience 

 a " new sensation." What the blase man of the world 

 complains of is this accumulation, or rather persistence, 

 of his experiences. A repetition of the same stimulus 

 never again begets the same perception. The first 

 hearing of a modern drawing-room song may be 

 enjoyable, but the next time we hear it we are not 

 interested, and by-and-bye it becomes very tiresome. 

 The first hearing of a great symphony usually perplexes 

 us, and we are perhaps repelled by unusual harmonies, 

 or progressions, or strange modulations, but subsequent 

 hearings afford increasing pleasure. We say that there 

 was " so much in it " that we did not understand it, 

 yet precisely the same series of external stimuli affected 

 our auditory membranes on each occasion, and the 

 same molecular disturbances were transmitted along 

 our afferent nerves to the central nervous system, 

 where the same physical effects must have been pro- 

 duced. The difference in all these cases between the 



