Bennett returned to Edinburgh in 1841, and on the 1st October published “Treatise on the Oleum Jecoris Aselli, or Cod-liver Oil, as a Therapeutic Agent in certain Forms of Gout, Rheumatism, and Scrofula, with Cases.” His knowledge of this remedy had been acquired in Germany, where cod-liver oil was being used in the treatment of these diseases. Its use had however long been known among the Scotch fishing folk, and Drs. Kay and Bardsley had many years before prescribed it in the Manchester Infirmary. The publication, however, stagnated, and there was added in 1847 to the remaining copies an appendix of cases benefited by cod-liver oil. By this time its administration was decidedly on the increase, and one firm of druggists in Edinburgh had sold six hundred gallons in the preceding year, as compared with one gallon in 1841. At the same time Dr. C. J. B. Williams was introducing purer forms of the oil in London, as we have already related, and by his writings and practice and study of cases of pulmonary consumption did very much to promote its general use. In November 1841 Bennett started a course of lectures on histology at Edinburgh, in which he illustrated physiology and pathology by microscopical preparations: he also formed classes for private instruction in microscopical manipulation. At that time minute changes in structure were generally overlooked, and to Bennett belongs the credit of first giving such instruction in a systematic form. He strongly desired to gain the chair of General Pathology at Edinburgh, which was vacant in 1842, but he was unsuccessful. When he was soon afterwards appointed physician to the Royal Dispensary, Bennett had an opportunity of putting into practice what he had learnt in Germany, by establishing what he called a polyclinical course, his students being taught practically, under the eye of the teacher, to examine and prescribe for patients. It must not be forgotten, however, that Syme had previously introduced a somewhat similar procedure at his Minto House (Surgical) Hospital. As Pathologist to the Royal Infirmary, Bennett had great opportunities of studying morbid specimens, and he got together a large pathological collection. He further gave courses of lectures on pathology. For many years Bennett took a large part in maintaining the literary activity of the Edinburgh School. Many papers by him appeared in the _London and Edinburgh Monthly Journal of Medical Science_, of which he subsequently was part and sole proprietor two or three times, being so lucky as to make a profit on each of his transactions.