Here, for instance, is a parchment which contained some Grecian tragedy, the Agamemnon of AEschylus, or the Phoenissae of Euripides. This had possessed a value almost inappreciable in the eyes of accomplished scholars, continually growing rarer through generations. But four centuries are gone by since the destruction of the Western Empire. Christianity, with towering grandeurs of another class, has founded a different empire; and some bigoted yet perhaps holy monk has washed away (as he persuades himself) the heathen's tragedy, replacing it with a monastic legend; which legend is disfigured with fables in its incidents, and yet, in a higher sense, is true, because interwoven with Christian morals and with the sublimest of Christian revelations. Three, four, five, centuries more find man still devout as ever; but the language has become obsolete, and even for Christian devotion a new era has arisen, throwing it into the channel of crusading zeal or of chivalrous enthusiasm. The _membrana_ is wanted now for a knightly romance--for "my Cid," or Coeur de Lion; for Sir Tristrem, or Lybaeus Disconus. In this way, by means of the imperfect chemistry known to the mediaeval period, the same roll has served as a conservatory for three separate generations of flowers and fruits, all perfectly different, and yet all specially adapted to the wants of the successive possessors. The Greek tragedy, the monkish legend, the knightly romance, each has ruled its own period. One harvest after another has been gathered into the garners of man through ages far apart. And the same hydraulic machinery has distributed, through the same marble fountains, water, milk, or wine, according to the habits and training of the generations that came to quench their thirst.