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.
The yellow fever virus is in the genus Flavivirus, in the family Flaviviridae. Yellow fever is transmitted in jungle cycles between non-human primates and mosquitoes in jungles of South America and Africa, and in savannahs of Africa. Humans and monkeys are the principal animals to be infected.his favours epidemics of yellow fever. Infection causes a wide spectrum of disease, from mild symptoms to severe illness and death. The yellow in the name is explained by the jaundice that affects some patients, causing yellow eyes and yellow skin.