The canon law was closely associated with the civil, indeed for many purposes it was desirable to graduate in both these subjects as a _Doctor utriusque juris_, or as we say a J.U.D. or an LL. D. Canon law was condemned by the theologians as a “lucrative” subject, which drew students away from pure learning toward the path of ecclesiastical preferment. By the thirteenth century the mediaeval church was a vast administrative machine which needed lawyers to run it, and a well-trained canonist had a good chance of rising to the highest dignities.[6] No wonder canon law attracted the ambitious, the wealthy, even the idle, for at Paris we are told that the lazy students frequented the lectures of the canonists in the middle of the morning, rather than the other courses which began at six. The standard textbook in canon law was the _Decretum_ of Gratian, supplemented by the decretals of subsequent popes, especially the great collection which Gregory IX in 1234 distributed to the principal universities. The methods of studying these texts were the same as in the civil law, giving rise to the rich canonistic literature of the later Middle Ages and the marginal glosses for which, according to Dante, “the Gospel and the great doctors are deserted.” Of the textbooks needed in all these subjects the university undertook to secure a supply at once sufficient, correct, and cheap, for the regulation of the book trade was one of the earliest and most valued of university privileges. As books were costly they were commonly rented, at a fixed price per quire, rather than owned; indeed the sale of books was hedged in by close restrictions designed to curb monopoly prices and to prevent their removal from town. The earliest Paris tariff, ca. 1286, lists for rent copies of one hundred and thirty-eight different books. In course of time many students came to have books of their own--a Bible, or at least some part of it, a piece of the _Digest_, perhaps even the “twenty bokes clad in blak or reed” of Chaucer’s Oxford clerk. Whether rented or owned, the supply was not inconsiderable; on the Bolognese monuments each student has a book before him. So long as each copy had to be made by hand, accuracy was a matter of much importance, and the university had its supervisors and correctors who inspected periodically all the books for sale in the town. Moreover, at Bologna a constant supply of new books was secured by the requirement that every professor should turn over a copy of his repetitions and disputations to the stationers for publication. The principal books of law and theology were the natural outgrowth of university lectures. With demand and supply so largely concentrated in the universities, it is not surprising that these should have become the chief centres of the book trade and, as we should say, of the publishing business. So long as students could rent the books they required, there was less need for libraries than we might at first