Ronald Ross discovered the link between mosquitos and malaria transmission on 20 August 1897: "The work, which was continued from 8 a.m. to 3 or 4 p.m. with a short interval for breakfast, was most exhausting, and so blinding that I could scarcely see afterwards; and the difficulty was increased by the fact that my microscope was almost worn out, the screws being rusted with sweat from my hands and forehead, and my only remaining eye-piece being cracked, while swarms of flies persecuted me at their pleasure as I sat with both hands engaged at the instrument. / ... / The seventh dappled-winged mosquito was then successfully dissected. Every cell was searched, and to my intense disappointment nothing whatever was found, until I came to the insect’s stomach. Here, however, just as I was about to abandon the examination, I saw a very delicate circular cell apparently lying amongst the ordinary cells of the organ, and scarcely distinguishable from them. Almost instinctively I felt that here was something new.” From the 1902 Nobel Prize lecture by Ronald Ross. We can highly recommend reading his lecture even though it's 90 pages long: goo.gl/yNNtSr Image: The page in Ross' notebook where he recorded the "pigmented bodies" in mosquitoes that he later identified as malaria parasites.