Just how little consideration has been given to such matters in the past [as study into the effects of media] can be gathered from the consternation of one of the editors of this book [Understanding Media]. He noted in dismay that "seventy-five per cent of your material is new. A successful book cannot venture to be more than ten per cent new." Such a risk seems quite worth taking at the present time when the stakes are very high, and the need to understand the effects of the extensions of man becomes more urgent by the hour.