1901.] on Memory. 599 



or leave it long enough, and the sag will remain ; the set will become 

 permanent. 



The behaviour of wood under distortion may be summarised 

 thus: — 1. It is, within limits, elastic, and if distorted within these 

 limits it instantly recovers its shape when the distorting force ceases 

 to act. 2. If distorted beyond its elastic limit, it retains a temporary 

 set, which, after a time, diminishes with varying velocity. 3. If the 

 distortion, whether within or without the elastic limit, is sufficiently 

 prolonged, or repeated sufficiently often, the set becomes permanent. 

 4. The distortion produces in the wood such a change that subsequent 

 similar distortions are facilitated. 



So far as the present argument is concerned, the walking-cane, the 

 whip-stock, the bow, the fishing-rod aud the shelf may be looked upon 

 as not only organised but live. They are, so far as concerns the 

 reactions that we have considered, in the same state as when they 

 formed part of the living tree. If we subject a dead branch to similar 

 experiences, we find that it behaves in a totally different manner. It 

 takes no set, but breaks. Now, regarding the wood as live, it is 

 evident that if we could apply our observations on wood to other live 

 tissues, our task of investigating at least the structural and dynamic 

 memories of the human brain would be greatly facilitated. There is 

 a very large body of facts, of which but a very small selection can be 

 given here, which harmonise with this assumption, and indicate that 

 we may take it provisionally as a working hypothesis without any 

 great departure from likelihood. 



Every organism has its specific shape, and if it is distorted by a 

 transient agent, it will begin after a time to return to its normal 

 sbape, by degrees that at first are slow, for a short time increase in 

 speed, and thereafter continually diminish in velocity. But if the 

 distortion is very great, or is very often repeated, or is long continued, 

 then the set becomes permanent. 



A tree which is exposed to a prevailing wind, or which is darkened 

 on one side, will grow lop-sided ; and if it is exposed long enough to 

 these conditions the distortion will be permanent. But if, while the 

 tree is young enough, that is, before the distorting agent has acted 

 too long, its action is arrested, the tree will, after a pause, begin to 

 recover its symmetrical shape ; and it will recover by stages which 

 at first increase in speed, and then become year by year slower and 

 slower. Nay, if the distortion is increased to actual disruption the 

 same redintegration often takes place. If the branch of a tree be 

 broken, or if a limb is torn off a crab or a lobster, the set that is 

 produced is not a permanent set. After a pause, the lost part begins 

 to grow again, and the growth at first increases in speed, and there- 

 after diminishes until it becomes imperceptibly slow, so that the re- 

 produced part does not for long, perhaps does not ever, attain to the 

 dimensions of the lost part. 



Moreover, it is to be noticed that in proportion to the immaturity 

 of the part in course of construction is its vulnerability. The green 



