The arbitrary order of the university, which compelled the booksellers to lend their books to scholars, shows that it was customary for a student or a poor man of letters to copy the books he needed. The little books sold for a sol were manifestly made for readers who could not even buy the vellum [p164] required for a book of the usual size. It was necessary that books sold at this price should be of the cheapest materials, and that the text should be abbreviated by contractions[78] so that it would occupy but little space. The despised fabric of paper, and the remnants of vellum rejected by professional copyists after the skin had been cut up for leaves of folio or of quarto size, were cheerfully accepted by readers who valued a book more for its contents than for its appearance. The scarcity of vellum in one century, and its abundance in another, are indicated by the size of written papers during the same periods. Before the sixth century, legal documents were usually written upon one side only; in the tenth century the practice of writing upon both sides of the vellum became common. During the thirteenth century, valuable documents were often written upon strips two inches wide and but three and a half inches long. At the end of the fourteenth century these strips went out of fashion. The more general use of paper had diminished the demand for vellum and increased the supply. In the fifteenth century, legal documents on rolls of sewed vellum twenty feet in length were not uncommon. All the valuable books of the fourteenth century were written on vellum. In the library of the Louvre the manuscripts on [p165] paper, compared to those on vellum, were as one to twenty-eight; in the library of the Dukes of Burgundy, one-fifth of the books were of paper. The increase in the proportion of paper books is a fair indication of the increasing popularity of paper; but it is obvious that vellum was even then considered as the more suitable substance for a book of value.