In any civilization there will be found something in the way of esoteric knowledge. This body of knowledge will vary characteristically from one culture to another, differing both in content and in respect of the canons of truth and reality relied on by its adepts. But there is this common trait running through all civilizations, as touches this range of esoteric knowledge, that it is in all cases held, more or less closely, in the keeping of a select body of adepts or specialists—scientists, scholars, savants, clerks, priests, shamans, medicinemen—whatever designation may best fit the given case.