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 gravity, "and I lament your lack of mental initiative. However, the points that this case illustrates are these: First, the danger of delay; the vital importance of instant action before that frail and fleeting thing that we call a clue has time to evaporate. A delay of a few hours would have left us with hardly a single datum. Second, the necessity of pursuing the most trivial clue to an absolute finish, as illustrated by the spectacles. Third, the urgent need of a trained scientist to aid the police; and, last," he concluded, with a smile, "we learn never to go abroad without the invaluable green case."