At the very end of the Middle Ages came the father of modern pharmaceutical chemistry, Basil Valentine. Already the spirit that was to mean so much for scientific investigation in the Renaissance period was abroad. Valentine, however, owes little to anything except his own investigations, and they were surprisingly successful, considering the circumstances of time and place. His practical suggestions so far as drugs were concerned did not prove to have enduring value, but then this has been a fate shared by many of the masters of medicine. There were many phases of medical practice, however, that he insisted on in his works. He believed that the best agent for the cure of the disease was nature, and that the physician's main business must be to find out how nature worked, and then foster her efforts or endeavor to imitate them. He insisted, also that personal observation, both of patients and drugs, was more important than book knowledge. Indeed, he has some rather strong expressions with regard to the utter valuelessness of book information in subjects where actual experience and observation are necessary. It gives a conceit of knowledge quite unjustified by what is really known. What is interesting about all these men is that they faced the same problems in medicine that we have to, in much the same temper of mind that we do ourselves, and that, indeed, they succeeded in solving them almost as well as we have done, in spite of all that might be looked for from the accumulation of knowledge ever since. It was very fortunate for the after time that in the period now known as the Renaissance, after the invention of printing, there were a number of serious, unselfish scholars who devoted themselves to the publication in fine printed editions of the works of these old-time makers of medicine. If the neglect of them that characterized the eighteenth and early nineteenth centuries had been the rule at the end of the fifteenth and during the sixteenth century, we would almost surely have been without the possibility of ever knowing that so many serious physicians lived and studied and wrote large important tomes during the Middle Ages. For our forefathers of a few generations ago had very little knowledge, and almost less interest, as to the Middle Ages, which they dismissed simply as the Dark Ages, quite sure that nothing worth while could possibly have come out of the Nazareth of that time. What they knew about the people who had lived during the thousand years before 1500 only seemed to them to prove the ignorance and the depths of superstition in which they were sunk. That medieval scholars should have written books not only well worth preservation, but containing anticipations of modern knowledge, and, though of course they could not have known that, even significant advances over their own scientific conditions, would have seemed to them quite absurd.