"From 1815 to 1817 Maclean travelled in Spain, Turkey, and the Levant, and he studied the plague at the Greek Pest Hospital at Constantinople, in the service of the Levant Company. His experiences in the Levant and in India provided the basis for his most important medical work, The Results of an Investigation Respecting Epidemic and Pestilential Diseases (1817). Here Maclean restated his opposition to the theory that epidemic diseases were contagious, adding that the quarantine measures then imposed routinely in most Mediterranean ports against vessels sailing from the Levant had no basis in medical fact" (ODNB).  Digital facsimile from the Internet Archive at this link.