During his last year at Edinburgh the young physician, attracted towards London practice, was prudently weighing the cost and risk of such an enterprise. He decided in favour of a more modest course of provincial practice, waiting till his book on Diagnosis should be matured. As in later life, so now he was “strong in hope, inflexible for truth and justice, but inexperienced in the ways of the world, and unable to cope with the cunning, or to dissemble with the false.” After a visit to Paris for some months he proceeded to Göttingen and on to Berlin to visit the medical schools, walking alone and on foot from Paris to Göttingen, more than six hundred miles, in November 1814. After a brief period of practice in Bridgewater he commenced practice at Nottingham in February 1817, and with remarkable rapidity attained a leading position. In 1817 his work on the Diagnosis of Diseases appeared, and at once marked him out as a man of the highest originality, applying accurate observation and classification of symptoms to the detection and distinction of diseases. Of this book the _Lancet_ of August 15, 1857, remarked: “Comprehensive, lucid, exact, and reliable, this work has, in the main, stood the test of forty years’ trial. A better has not been produced.” When Dr. Baillie, nephew of John Hunter and President of the College of Physicians, first saw Marshall Hall, he complimented him on being the son of the author of so extraordinary a work as that on Diagnosis. Being modestly told that he himself was the author, Baillie exclaimed: “Impossible! it would have done credit to the greyest-headed philosopher in our profession.”