Ricin immunogenic in mice, rabbits, and humans. It has completed two successful clinical trials. Ricin has been involved in a number of incidents. In 1978, the Bulgarian dissident Georgi Markov was assassinated by Bulgarian secret police who surreptitiously shot him on a London street with a modified umbrella using compressed gas to fire a tiny pellet contaminated with ricin into his leg. He died in a hospital a few days later and his body was passed to a special poison branch of the British Ministry of Defence (MOD) that discovered the pellet during an autopsy. The prime suspects were the Bulgarian
Umbrella gas used by riot police. In the 1950s Frei Otto transformed the universally used individual umbrella into an item of lightweight architecture. He developed a new umbrella form, based on the minimum surface principle. The tension loaded membrane of the funnel-shaped umbrella is now stretched under the compression-loaded bars. This construction type made it technically and structurally possible to build very large convertible umbrellas. The first umbrellas of this kind (Federal Garden Exhibition, Kassel, 1955) were fixed, Frei Otto constructed the first convertible large umbrellas for the Federal Garden Exhibition in Cologne 1971. In 1978 he built a group of