We have seen that the number of books printed in Cracow alone in the years 1503-1536 was two hundred ninety-four. The total number of books printed in Poland toward the end of the fifteenth and during the sixteenth century is estimated to have been seven thousand five hundred.[224] This extensive printing and publishing activity contributed greatly to the popularization and spread of the ideas of humanism and the doctrines of the Reformation. Then, too, the spread of the new ideas in Poland was due to close intellectual connections between Poland and the West and to the influence of German and Swiss universities. It was customary for the sons of the Polish aristocracy and the well-to-do gentry to frequent foreign universities for the purpose of rounding out their education. The leaders of that day, whether in science, literature, or politics, were invariably men educated abroad. Moreover, visits home on the part of the Polish students, regardless of whether they were studying in Germany, Switzerland, or Italy, were more common and frequent in the sixteenth century than today.[225] The University of Cracow, famous for its learning, attracting students from all over Europe, and flourishing in the fifteenth century, lost its influential position and its drawing power with the beginning of the sixteenth century, owing to its reactionary character and its pronounced opposition to the new current of thought and learning. The universities of the West and of the South superseded it in influence and attractiveness. The flow of foreign students to Cracow ceased; and Polish students began to turn now more and more to German, French, Swiss, and Italian universities in search of learning and knowledge.[226] Up to 1525 the sons of distinguished Polish families still frequented the University of Cracow, spending their first years there and then finishing their studies in universities abroad. After that, however, the character of the student body at the university changed entirely. The sons of the Polish aristocracy disappeared; they turned to other universities. The names appearing on the university register after 1525 were names of the small gentry, the town population, and the peasantry.[227] The youth of the Protestant families in particular had nothing to gain by registering at the University of Cracow; it, therefore, sought the universities of Wittenberg, Zurich, and Basel, especially so by the middle of the sixteenth century.[228]