1. http://www.ancienttexts.org/library/mesopotamian/gilgamesh/tab11.htm.
2. Sappho, fragment 58. See for example http://www-personal.umich.edu/∼rjanko/Tithonus%20Eos%20and%20the%20cicada.pdf.
3. Propertius, Elegies 2.18b. http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A2008.01.0494%3Abook%3D2%3Apoem%3D18b.
4. Living to 120 and beyond: Americans' views on aging, medical advances and radical life extension. Pew Research Center; https://www.pewresearch.org/religion/2013/08/06/living-to-120-and-beyond-americans-views-on-aging-medical-advances-and-radical-life-extension/.
5. Emergence and reemergence of smallpox: the need for development of a new generation smallpox vaccine;Shchelkunov;Vaccine,2011