All that concerns us here, however, is to note that this panegoistic extreme of thought exhibits the same paradox as the other extreme of materialism.  It is equally complete in theory and equally crippling in practice.  For the sake of simplicity, it is easier to state the notion by saying that a man can believe that he is always in a dream.  Now, obviously there can be no positive proof given to him that he is not in a dream, for the simple reason that no proof can be offered that might not be offered in a dream.  But if the man began to burn down London and say that his housekeeper would soon call him to breakfast, we should take him and put him with other logicians in a place which has often been alluded to in the course of this chapter.  The man who cannot believe his senses, and the man who cannot believe anything else, are both insane, but their insanity is proved not by any error in their argument, but by the manifest mistake of their whole lives.  They have both locked themselves up in two boxes, painted inside with the sun and stars; they are both unable to get out, the one into the health and happiness of heaven, the other even into the health and happiness of the earth.  Their position is quite reasonable; nay, in a sense it is infinitely reasonable, just as a threepenny bit is infinitely circular.  But there is such a thing as a mean infinity, a base and slavish eternity.  It is amusing to notice that many of the moderns, whether sceptics or mystics, have taken as their sign a certain eastern symbol, which is the very symbol of this ultimate nullity.  When they wish to represent eternity, they represent it by a serpent with his tail in his mouth.  There is a startling sarcasm in the image of that very unsatisfactory meal.  The eternity of the material fatalists, the eternity of the eastern pessimists, the eternity of the supercilious theosophists and higher scientists of to-day is, indeed, very well presented by a serpent eating his tail, a degraded animal who destroys even himself.

This chapter is purely practical and is concerned with what actually is the chief mark and element of insanity; we may say in summary that it is reason used without root, reason in the void.  The man who begins to think without the proper first principles goes mad, the man who begins to think at the wrong end.  And for the rest of these pages we have to try and discover what is the right end.  But we may ask in conclusion, if this be what drives men mad, what is it that keeps them sane?  By the end of this book I hope to give a definite, some will think a far too definite, answer.  But for the moment it is possible in the same solely practical manner to give a general answer touching what in actual human history keeps men sane.  Mysticism keeps men sane.  As long as you have mystery you have health; when you destroy mystery you create morbidity.  The ordinary man has always been sane because the ordinary man has always been a mystic.  He has permitted