Pneumococci growing on blood agar, illustrating α hemolysis and optochin sensitivity (zone around optochin disk). Inset: Gram’s stain, illustrating gram-positive diplococci. (Photographs courtesy of Paul Turner, University of Oxford, United Kingdom.) Source: PNEUMOCOCCAL INFECTIONS, Harrison's Infectious Diseases, 3e Citation: Kasper DL, Fauci AS. Harrison's Infectious Diseases, 3e; 2017 Available at: http://accessbiomedicalscience.mhmedical.com/DownloadImage.aspx?image=/data/books/2073/harid3_ch42_f001.png&sec=156819368&BookID=2073&ChapterSecID=156819362&imagename= Accessed: November 08, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved