IN THE YEAR OF THE PLAGUE (It is known that some ancient Roman coins have medical instruments on them. My only image of a microscope on a coin is a Zeiss commemorative that I do not own. My Zeiss commemoratives are postage stamps, a different collectible entirely. Just to say that these examples are circulated world banknotes but the topic is open.) Darwin is iconically famous. Pasteur is well known but well worth reading more about as you wish. He was a chemist who took an interest in a problem with wine and went from there to anthrax and rabies. Oswaldo Gonçalves Cruz is less well known. "Cruz found the seaport of Santos ravaged by an epidemic of bubonic plague that threatened to reach Rio de Janeiro and engaged himself immediately in the combat of this disease. The mayor of Rio de Janeiro authorized the construction of a plant for manufacturing the serum against the disease which had been developed at the Pasteur Institute by Alexandre Yersin and coworkers. He asked the institution for a scientist who could bring to Brazil this know-how. The Pasteur Institute responded that such a person was already available in Brazil: Dr. Oswaldo Cruz." -- https://en.wikipedia.org/wiki/Oswaldo_Cruz Collectors of American coins may know John Leonard Riddell, chief melter at the New Orleans Mint and the author of Monograph on the Silver Dollar which identified many circulating counterfeits of the 1840s. Riddell was a scientist, inventor of the binocular microscope and a firm advocate of the germ theory of disease at a time when it was argued against. (See, also, the professional life of Pasteur.) m.