If to MacArthur and John Reid was due the credit of first directing Simpson's thoughts to the study of medicine, to Professor John Thomson belongs the credit of having made him an obstetrician. "At Dr. Thomson's earnest suggestion and advice," says Simpson, "I first turned more especially to the study of midwifery with the view of becoming a teacher of this department of medical science." He lost no time in throwing himself heartily into the work that was nearest to him, and became almost indispensable to his chief. Most of his time was spent in the Pathological Museum, busily engaged in arranging, classifying, and describing the preparations, but he also assisted in preparing the professor's lectures. He took up more readily than Thomson the then new mode of study by the microscope, and it is related that once he composed a lecture for his chief on this subject which Thomson delivered without previous perusal. Several times as Thompson read the lecture to the class he looked up to glare at his assistant, and when they returned to the side room he shook his fist in his face, saying, "I don't believe one d--d word of it." Although Simpson was now earning enough by his salary as assistant to meet his expenses at the time, his family maintained their loving interest in his welfare. His sister told him he was working too hard and hurting his health. "Well," he replied, "I am sure it is just to please you all." Sandy, who had married in 1832, watched his career carefully, and when the cholera made its appearance in Scotland he made a will with a provision for "my dear James" in the event of his death. "I daresay," he addressed his family therein, "every one of you has a pleasure in doing him good by stealth as I have had myself."