This depends on the condition of the bill. In normal used condition, they are worth exactly $2. $2 bills dated 1976 and newer are the ones worth face value only. The $3/$4 figure is reasonable for bills dating back to the 1950s.
Klein thought he had, discovered the poison to be due to a disease of the cow. An epidemic of scarlet fever broke out in London in December, 1885, and the outbreak could be traced to the milk supplied by a herd in Hendon.
It is thought that the disease originated in Africa and spread to the Americas in the 17th and 18th centuries through trading ships. The flavivirus that causes yellow fever was first identified in 1928 and the first vaccine against the disease was produced at the Rockefeller Institute in New York in 1937.