Livingstone, David, 1813-1873. Letter to Thomas B. Johnston, 3 October 1857. Images copyright Wellcome Library, London. Creative Commons Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/). As relevant, copyright Dr. Neil Imray Livingstone Wilson. Creative Commons Attribution-NonCommercial 3.0 Unported (https://creativecommons.org/licenses/by-nc/3.0/). 