vii ASSIMILATION AND READJUSTMENT 109 



necessarily learnt anything by experience of results. Thus 



any organism, from Protozoa to man, is likely to tolerate 



unusual heat or cold better after a certain amount of 



exposure to it than at first. 1 But we do not tolerate 



extreme heat better because we have found its effects to 



be beneficial. The exposure puts a certain strain on the 



organism. If the organism responds to the strain, and 



does not sink under it, it is able to bear a similar strain 



better a second time. We are not, without further 



evidence, warranted in attributing such a change to 



experience of the results of such a response. For it is 



part of the general law of organic adaptability that a thing 



done once is more easily done a second time, and a thing 



suffered once is, if recovery is complete, more easily 



suffered a second time. So far as this law applies, the 



organism is modified not by experience of the consequences 



of what it does, but by the doing itself. Many of the 



effects of practice and exercise seem to be referable to the 



direct influence, as we may call it, of experience. Thus, 



as we have seen, many reflexes are more or less imperfect 



at birth, and are improved by practice. But it does not 



follow that the improvement is due to experience of the 



results of the reflex. In any exercise involving strength 



in a particular muscle we improve with practice because 



the muscle itself grows stronger, and it grows stronger, 



not because we find that it is better so, but through a 



reflex arrangement by which exercise increases its blood 



supply, that is to say, secures it more nourishment. 2 In 



the same way there is every probability that a reflex 



mechanism improves not only through the confirmation of 



well adapted actions and the inhibition of others, but also 



because usage makes the different parts work better 



together. In learning to ride a bicycle, we are told to 



turn to the side towards which we are beginning to fall. 



We do this at first consciously and awkwardly. By 



degrees we respond at once more rapidly and more gently 



1 For adaptation of this sort among Protozoa see Verworn, Prot. S/.; 

 for Fiagellata, p. 42 ; Stentor, p. 72, &c. 



2 This is, of course, a result of the exercise, but it is not through 

 learning that this result follows that we modify our use of the limb, but 

 the result itself is such as to give us an improved limb. 



