Manchester Memoirs, Vol. xlii. (1898), No. \%, 45 



fested in the grosser changes which we call growth. But 

 such large effects are nothing more than the summation 

 of smaller changes ; to produce the total each contri- 

 bution must have brought its share. And we shall 

 probably not err in supposing that every influence 

 brought to bear on a nerve unit produces an effect which 

 lasts far beyond the passing functional activity. When 

 light falls on sensitive retina for a moment only the effect 

 on the higher parts of the visual mechanism may be traced 

 long afterwards, under favourable circumstances, as a 

 gradually fading series of images alternating with rests or 

 rather with reversions, and even when the effects have 

 fallen below the threshold of consciousness, and thus 

 seem to have passed away, a study of the results of a 

 fresh stimulation shows that the machinery is not yet at 

 rest, is not as yet what it was before. Moreover, 

 the finer our means of testing, the longer may we 

 trace out the effects. Yet, in this visual mechanism 

 which supplies the earlier links of the nervous chain 

 for the production of psychical effects, which has to 

 be used again and again in order to feed the higher, 

 more distinctly psychical links, there must, we may 

 suppose, be agencies at work tending to wipe out all 

 previous effects in order to prepare for new events. In 

 the higher links the need of such tergative agencies will, 

 we may further suppose, become less and less. If so, in 

 them we may fairly expect that the effect of an influence 

 once brought to bear will last far longer, will last long 

 enough, may I say, to give us a glimpse of seeing what 

 may be the physical basis of the psychical fact of memory. 

 One word more. In the lower tissues, in undifferenti- 

 ated protoplasm, in muscle and the like, spontaneous 

 activity, automatism seems to be the direct outcome of 

 nutrition, the direct effect of the blood supply working on 

 the molecular machinery, and to be independent of the 



