Types. Economists Ronald G. Ehrenberg and Robert Smith, authors of Modern Labor Economics, identify two main types of labor unions: craft unions and industrial unions. Craft unions represent workers in a specific occupation.lthough union membership in the United States peaked in the mid-20th century and has declined since then, various types of labor unions remain an influential force in American business and politics.
U.S. Army Physicians Discovered the Cause of Yellow Fever. August 27, 1900. No one knew what caused the often-deadly yellow fever, but it occurred in epidemic proportions, with one person after another in a given area becoming sick. People feared the mysterious disease, until U.S. Army physician James Carroll endangered his own health in the name of science.
Knowledge center. Yellow fever is an acute systemic illness-a hemorrhagic fever-caused by the Flavivirus. Acute means it comes on (onset) rapidly, while systemic means it affects the whole body. In severe cases yellow fever causes a high fever, bleeding into the skin and the death of cells in the liver and kidneys.ellow fever is caused by a flavivirus; it is transmitted by the bite of mosquitoes, usually the Aedes aegypti mosquito, which had become infected by biting an infected human or animal (a monkey). An infected mosquito is a source of infection for the rest of its life.