In this movement, naturally, the printing-press played an all-important part.

Medical books, hitherto practically inaccessible to the great mass of physicians, now became common, and this output of reprints of Greek and Arabic treatises revealed the fact that many of the supposed true copies were spurious.

These discoveries very naturally aroused all manner of doubt and criticism, which in turn helped in the development of independent thought.
A certain manuscript of the great Cornelius Celsus, the De Medicine, which had been lost for many centuries, was found in the church of St.
Ambrose, at Milan, in 1443, and was at once put into print.

The effect of the publication of this book, which had lain in hiding for so many centuries, was a revelation, showing the medical profession how far most of their supposed true copies of Celsus had drifted away from the original.

The indisputable authenticity of this manuscript, discovered and vouched for by the man who shortly after became Pope Nicholas V., made its publication the more impressive.