These were stirring times in Edinburgh medical circles. The strong, cool demeanour of Knox under the persecutions to which he was subjected, must have made an indelible impression on Simpson's mind, and the memory of it may have served to strengthen him in later years when himself subjected to the unjust accusations of thoughtless and ignorant people. One night when Knox had attracted a large class to hear him on a favourite subject, the crowd in the street mustered in unusual force; the yells and howls from outside were heard distinctly in the class-room. The students got alarmed, and kept looking to the doors of egress. Knox perceiving the restlessness and alarm of his audience paused, and then addressed to them reassuring words, expressing his contempt for the cowardly mob, and reminding them of the great men who at different times had suffered persecution for the cause of their science. His statement was received with such cheers as resounded beyond the class-room walls and actually cowed the uproarious mob, so loudly did the students applaud the words of the man who, they knew, daily placed his life in danger in order to lecture to them, and whose last hour seemed to have come, so great and threatening was the crowd on this particular evening. If Simpson did not actually witness such a scene as the foregoing--he was not a member of Knox's class until the session 1830-31--he must at least have known full well about it at the time, and shared with the whole body of students the worship of the man as a hero. His fellow lodger, Reid, was not only a distinguished pupil in Knox's class, but became one of Knox's demonstrators in 1833, and was always a prominent Knoxite. We know also that Knox went down to Bathgate to visit Reid's relations there, so that it is justifiable to conclude that Simpson came closely in contact with this remarkable teacher. That the relationship between Reid and Simpson was most intimate we have the former's own words for. At a public dinner given to him when appointed to his professorship in 1841, he said, "In the croupier (Simpson) I recognise my earliest friend, a native of the same village. We were rivals at school and at college. We stood to each other from boyhood upwards in every possible relation, whether of an educational, warlike, delicate, or social character, which the warm and fitful feelings peculiar to boyhood and youth can produce."