At Oxford he formed a close friendship with John Locke, better known afterwards as a philosopher than as a physician. Their intimacy, which lasted to the end of Sydenham’s life, probably contributed not a little to give form to the disgust which he soon displayed at the unsatisfactory and fluctuating state of medical opinion, and to the zeal with which he sought to establish it on surer grounds; for he appeals, as to the highest authority, in confirmation of some of his new views on the treatment of fever, to the approval of his illustrious friend, who even paid him the compliment of prefixing a eulogy in indifferent Latin verse to the treatise in which these views are developed. On the 14th of April, 1648, he took the degree of bachelor of medicine, being then twenty-four years old; and in the same year obtained a fellowship at All Souls College, by the interest of a relation. The degree of doctor he subsequently took at Cambridge, where, being among those who thought with him in politics, he probably found himself more at his ease. After a visit of some length at Montpellier, then considered the best practical school of medicine on the continent, he settled in Westminster, and soon after married. His progress to eminence in his profession must have been unusually rapid, which might be owing, in some measure, to the call for men of good capacity to the more stirring scenes of civil strife; for at thirty-six he had succeeded in establishing a first-rate reputation, which he continued to sustain in spite of much hostility and ill-health for upwards of twenty years. He witnessed the breaking out of the plague in 1665, but when it reached the house adjoining his own, he was induced to remove with his family some miles out of town. Of this desertion of his post, however, he seems to have repented; for he afterwards returned, and occupied himself diligently in visiting the victims of that devastating malady, and has left a short but interesting account of his opinions respecting it, and of the treatment he adopted; for the comparative success of which, he appeals to the physicians who had witnessed or followed his practice. At the age of 25, though a man of remarkably temperate and regular habits, he became afflicted with gout and stone, from which he suffered extreme torment with great resignation and patience for the rest of his life. Of course he did not neglect the opportunity of studying those diseases in his own person, and recording the result of his observations. His account of gout, especially, is considered to be a most accurate and able history of that disease.