Cusanus' life and work stand, then, as a type of the accomplishment, the opportunities, the power of thought, the practical scholarship, the mathematical accuracy, the fine scientific foresight of a scholar of the fifteenth century. For us, in medicine, it is interesting indeed to realize that it is from a man of this kind that a great new departure in medicine with regard to the employment of exact methods of diagnosis had its first suggestion in modern times. The origin of that suggestion is typical. It has practically always been true that it was not the man who had exhausted, or thought that he had done so, all previous medical knowledge, who made advances in medicine for us. It has nearly always been a young man early in his career, and at a time when, as yet, his mind was not overloaded with the medical theories of his own time. Cusanus was probably not more than thirty when he made the suggestion which represents the first practical hint for the use of laboratory methods in modern medicine. It came out of his thoughtful consideration of medical problems rather than from a store of garnered information as to what others thought. It is a lesson in the precious value of breadth of education and serious training of mind for real progress at all times. XIV BASIL VALENTINE, LAST OF THE ALCHEMISTS, FIRST OF THE CHEMISTS "Fieri enim potest ut operator erret et a via regia deflectat, sed ut erret natura quando recte tractatur fieri non potest." "For it is quite possible that the physician should err and be turned aside from the straight (royal) road, but that nature when she is rightly treated should err is quite impossible." This is one of the preliminary maxims of a treatise on medicine written by a physician born not later than the first half of the fifteenth century, and who may have lived even somewhat earlier. We are so prone to think of the men of that time as utterly dependent on authority, not daring to follow their own observation, suspecting nature, and almost sure to be convinced that only by going counter to her could success in the treatment of disease be obtained, that it is a surprise to most people to find how completely the attitude of mind, that is supposed to be so typically modern in this regard, was anticipated full four centuries ago. There are other expressions of this same great physician and medical writer, Basil Valentine, which serve to show how faithfully he strove with the lights that he had to work out the treatment of patients, just as we do now, by trying to find out nature's way, so as to imitate her beneficent processes and purposes. It is quite clear that he is but one of many faithful, patient observers and experimenters--true scientists in the best sense of the word--who lived in all the centuries of the Middle Ages.