PHYSICAL ACTIVITY. The difference between sticks and stones and living beings consists primarily in the fact that the latter are positively active; the former are passively acted upon. The stone will stay put, unless moved by some external agent, but even the amoeba will do something to its environment. It will stretch out pseudopodia to reach solid objects to which to cling; it will attempt to return to these objects when dislodged; it will actively absorb food. Higher up in the animal scale, "Rats run about, smell, dig, or gnaw, without real reference to the business in hand. In the same way Jack (a dog) scrabbles and jumps, the kitten wanders and picks, the otter slips about everywhere like ground lightning, the elephant fumbles ceaselessly, the monkey pulls things about."[2] "The most casual notice of the activities of a young child reveals a ceaseless display of exploring and testing activity. Objects are sucked, fingered and thumped; drawn and pushed, handled and thrown."[3] [Footnote 2: Hobhouse: _Mind in Evolution_, p. 195.] [Footnote 3 Dewey: _How We Think_, p. 31.] When vitality is at its height in the waking period of a young child, its environment is a succession of stimulations to activity. Man's "innate tendency to fool" is notorious, a tendency particularly noticeable in children. Objects are responded to, not as means to ends, not with reference to their use, but simply for the sheer satisfaction of manipulation. Facial expressions, sounds, gestures, are made almost on any provocation; they are the expressions of an abundant "physiological uneasiness." The two-year-old is a mechanism that simply must and will move about, make all kinds of superfluous gestures and facial expressions, and random sounds, as it were, just to get rid of its stored-up energy. Man's laziness and inertia are not infrequently commented on by moralists, but it is not laziness and inertia _per se_; certainly in normal individuals in the temperate zone, to do _something_ most of their waking time is a natural tendency and one intrinsically pleasant to practice. That the tendency to be active should vary in different individuals and at different times is, of course, as important a fact as it is a familiar one. Some of the causes of this variation will be noted in the succeeding. In adult life for casual and random activity is substituted activity directed by some end or purpose which determines the responses called into play. Professional and business, domestic and social enterprises and obligations take up most of the adult's energy. The contrast between the play of the child and the work of the adult is that in the case of the former actions are done for their own sake; and in the latter for some end. The child, we say, plays "for the fun of the thing," the adult works for pay, for professional success, for power, reputation, etc.