"The individual metabolism," as a distinguished authority in this field has expressed it, "is the reproductive metabolism."[18] Thus the establishment of our complete activities as human beings in the world is aided by, if not indeed ultimately dependent upon, a perpetual and many-sided play with our environment.
[18] W.Blair Bell, _The Sex-Complex,_ 1920, p.108.This book is a cautious and precise statement of the present state of knowledge on this subject, although some of the author's psychological deductions must be treated with circumspection.
It is thus that we arrive at the importance of the play-function, and thus, also, we realise that while it extends beyond the sexual sphere it yet definitely includes that sphere.

There are at least three different ways of understanding the biological function of play.

There is the conception of play, on which Groos has elaborately insisted, as education: the cat "plays" with the mouse and is thereby educating itself in the skill necessary to catch mice; all our human games are a training in qualities that are required in life, and that is why in England we continue to attribute to the Duke of Wellington the saying that "the battle of Waterloo was won on the playing fields of Eton." Then there is the conception of play as the utilisation in art of the superfluous energies left unemployed in the practical work of life; this enlarging and harmonising function of play, while in the lower ranges it may be spent trivially, leads in the higher ranges to the production of the most magnificent human achievements.

But there is yet a third conception of play, according to which it exerts a direct internal influence--health-giving, developmental, and balancing--on the whole organism of the player himself.

This conception is related to the other two, and yet distinct, for it is not primarily a definite education in specific kinds of life-conserving skill, although it may involve the acquisition of such skill, and it is not concerned with the construction of objective works of art, although--by means of contact in human relationship--it attains the wholesome organic effects which may be indirectly achieved by artistic activities.