When Dr. Christison was about to leave Paris, Dr. Gregory’s death led to a vacancy in the Chair of Medical Jurisprudence at Edinburgh, and Christison was proposed to fill it while still absent. It is significant of the state of knowledge that not one of the candidates besides Christison had any practical knowledge of chemistry. The influence of Lord Melville, however, who had been his father’s resident pupil when young Christison was born, was the determining cause of his success in the election. At first students were very few, not half-a-dozen attending the earliest course. Christison devoted himself with characteristic energy to make his chair a real influence in the university. And here we may remark briefly on the extraordinary vigour of constitution which the new professor possessed, and retained almost till death. He could walk, run, or row better and with more endurance than any man of his time in Edinburgh, and that is saying a great deal. He made his new chair his primary object. Being an extremely neat and clean worker in the laboratory, his investigations soon became noted, and it was found, when he was called in to give evidence on matters of medical jurisprudence, especially in poisoning cases, that his mind was equally clear and accurate, and that he could give reasons for his beliefs which rendered his statements unimpeachable. From the famous trial of Burke and Hare in 1829 down to 1866 Dr. Christison appeared as a scientific witness in almost every case of medico-legal importance in Scotland, and in many in England. “As a witness,” says the _Scotsman_ (Jan. 28, 1882), “he was remarkable for a lucid precision of statement, which left no shadow of doubt in the mind of court, counsel, or jury as to his views. Another noteworthy characteristic was the candour and impartiality he invariably displayed, and which, backed as it was by the confidence that came of mature deliberation, rendered him almost impregnable to cross-examination. This was notably illustrated in the celebrated Palmer trial. Some of the medical witnesses for the Crown had got so severely handled by the prisoner’s counsel that the case seemed in danger of breaking down, but Christison had not been long in the box when the lawyers found they had at last met one who was a match for the subtlest of them: and so complete was the failure of all their efforts to discredit his evidence, that the case, by the time he finished, had assumed the gravest possible complexion.”