Smallpox vaccine Smallpox vaccine Smallpox vaccine, the first successful vaccine to be developed, was introduced by Edward Jenner in 1796. He followed up his observation that milkmaids who had previously caught cowpox did not later catch smallpox by showing that inoculated cowpox protected against inoculated smallpox. Dryvax is a freeze-dried calf lymph smallpox vaccine. It is the world's oldest smallpox vaccine, created in the late 19th century by American Home Products, a predecessor of Wyeth. By the 1940s, Wyeth was the leading US manufacturer of the vaccine and the only manufacturer by the 1960s. After world health authorities declared smallpox had been
Usable fuel zero. Although the term is mainly used in aviation it is sometimes also used for other craft with engines. Usable fuel In aviation, usable fuel is the fuel on board an aircraft that can actually be used by its engines. The opposite of usable fuel is unusable fuel. The unusable fuel figure is calculated for an aircraft fuel tank in "the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank". The figure usable fuel is used when calculating or defining other key figures of an aircraft such as MTOW, zero-fuel weight etc. Usable