If only mankind caught a glimpse of what infinite enjoyments, what perfect forces, what luminous reaches of spontaneous knowledge, what wide calms of our being lie waiting for us in the tracts which our animal evolution has not yet conquered, they would leave all and never rest till they had gained these treasures. But the way is narrow, the doors are hard to force, and fear, distrust and scepticism are there, sentinels of Nature to forbid the turning away of our feet from less ordinary pastures.