On his return to Salem, Dr. Oliver commenced the practice of medicine, and in July, 1811, as appears from his diary, he connected himself with Dr. R. D. Mussey, then a rising young surgeon, and with whom he was afterwards so long associated. From the following entry in the diary referred to, under date of July 12, 1812, may be learned somewhat of his tastes at this time, and his mode of passing the waiting hours of an early professional life: "This day completed the first year of my connection in the medical profession with Dr. R. D. Massey. On reviewing this period, I am sensible of a great loss of time, and of a degree of professional and literary improvement altogether inadequate to such an extent of time. Some improvement, however, has I hope, been made. With respect to the books which I have read during the past year, the most important are Mosheim's 'Ecclesiastical History,' which I have not yet quite completed,--a learned and judicious outline of the history of the church, embracing many collateral topics of learning and philosophy ...; Homer's 'Iliad' in Greek, with the exception of the last book; the 'Æneid' except the last two; two or three books of Livy, and several of Juvenal's 'Satires.' "The most important literary enterprise which I have undertaken and accomplished has been the delivery of a course of lectures on Chemistry in connection with Dr. Mussey. In Anatomy, also, we have executed something. Medicine will, in future, claim more of my attention, but not to the neglect of the two important collateral branches above mentioned." In the autumn of 1815, Dr. Oliver was appointed to deliver a course of chemical lectures before the medical class at Dartmouth College. Although he had thus far pursued the study of chemistry as a collateral branch of medical science, he felt warranted in accepting the appointment, without, however, proposing to himself a more permanent position in this department. In 1817, he was married to Miss Mary Robinson Pulling, the only daughter of Edward Pulling, Esq., an eminent barrister of Salem, and almost immediately went again to Philadelphia to avail himself of the advantages of that seat of medical learning, returning to Salem in the spring of 1818. In the following year he was induced to undertake, in connection with the Hon. John Pickering, the preparation of a Greek lexicon, a work involving much labor and research, and the larger portion of which fell to his lot. Although mainly based on the Latin of Schrevelius, many of the interpretations were new, and there were added more than two thousand new articles. The magnitude of the task and its successful accomplishment at once raised him to a conspicuous rank among the scholars of his day.