THE PURPOSE OF YOUTH 229 



thought of his own safety, and so exercises much more than his 

 ordinary strength. The events of some cases of somnambuhsm are 

 still more remarkable examples of what happens when the higher 

 ceUs of the brain are temporarily shut off from their control. Metch- 

 nikoff has collected a number of cases in which persons in the condi- 

 tion of somnambulism performed with sureness and agility feats 

 such as running up and down the steep roofs of houses, climbing 

 to places that they could not have reached and where they certainly 

 would not have retained their balance had they been in the normal 

 condition. He suggests that these are real returns to the automatic 

 fearlessness and semi-conscious gymnastics of the great apes. 



The period of youth in mammals is the time when the brain-cells 

 of the superficial grey matter increase in size, throw out fibres, 

 and come into more and more complex connection with each other 

 and with the different systems of the body. Just as the number 

 of these cells forms an index of the natural endowment of an 

 animal, so the extent to which these interconnections are developed 

 is a measure of the effect of education, in the widest sense of the 

 word. An animal with a smaller natural endowment might reach, 

 by a greater development of the initijJ stock, a higher mental plane 

 than another animal with many more cells that had remained 

 quiescent. No doubt a certain amount of development of these 

 cells takes place throughout the whole period of life, particularly 

 in the higher and more intelligent animals. But even in human 

 beings, at least in average cases, there appears to be comparatively 

 little further change in female brains after the age of fifteen, and 

 in male brains after that of twenty-four or twenty-five. In animals, 

 which after they have come to maturity seldom change the cha- 

 racter of their experiences or of their abilities much, it is probable 

 that the growth of the processes of the brain-cells practically is 

 limited to the period of youth. We may in fact say more definitely 

 that the period of youth is necessary for and is occupied by the 

 co-ordination of the brain-cells of the grey matter and the develop- 

 ment of a greater complexity of the intercommunications of these. 



We are on safer ground, however, when we turn from the physical 

 mechanism of the mind to the mental qualities themselves, and 

 consider the effect of education on these, without too nice an inquiry 

 as to what is education of the body and what is education of the 

 mental qualities. We like to think that animals have instinct and 

 that we have intelligence, but the passage from one to the other is 

 gradual. All instinct can be modified to a certain extent by expe- 



