Curiosity passes thus from casual rudimentary inquiry into genuinely scientific investigation. At first it is merely physical manipulation, then merely disconnected questionings; it becomes genuinely intellectual when it passes from "inquisitiveness" to inquiry. To be inquisitive means merely to want to know facts rather than to solve problems. To be scientifically inquiring is to seek on one's own account the significant relations between things. But these earlier and more casual forms of curiosity are not to be despised. If developed and controlled they lead to genuinely disinterested study of Nature and of men, to the spirit and the methods of science. That free play of imagination which was spoken of above as the chief source of original thinking and discovery is stimulated by an active hunting-out of new suggestions. Curiosity might also be defined as aggressive imagination, which, frequent enough in children, remains among adults to a pronounced degree only in geniuses of art and science. We may not agree with Bertrand Russell that "everything is done in education to kill it," but the dogmatism and fixity of mind which so soon settle down on maturity, the inability to be sensitive to new experiences, these are discouragingly familiar phenomena clearly inimical to science and to progress.
An active imagination that finds new materials to play over is the basis of both science and art. A skillful manipulation of its materials in words or sounds, colors, or lines makes its result art. Their controlled examination and systematization makes them science.
QUIESCENCE--FATIGUE. That all life, animal and human, is characterized by activity of a more or less persistent and positive kind has already been noted. But in human beings, as well as in animals, activity displays a "fatigue curve." The repeated stimulation of certain muscles produces fatigue toxins which impair the efficiency of response and make further stimulation painful. Of the causes of this lessened functional efficiency we may quote from Miss Goldmark's painstaking study:
During activity, as will be shown later, the products of chemical change increase. A tired person is literally and actually a poisoned person--poisoned by his own waste products. But so marvellously is the body constructed that, like a running stream, it purifies itself, and during repose these toxic impurities are normally burned up by the oxygen brought by the blood, excreted by the kidneys, destroyed in the liver, or eliminated from the body through the lungs. So rest repaires fatigue.[1]