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.
At the start of the twentieth century, the United States Army had a Yellow Fever Commission. The Army wanted medical experts to study yellow fever and find a way to stop the disease. One team went to Cuba to test the idea that mosquitoes spread yellow fever.The team was led by Walter Reed, the Army doctor and scientist noted for his work on infectious diseases.he was a nurse who worked with yellow fever patients in Cuba. Clara Maass was bitten by infected mosquitoes seven times between March and August of 1901. Only one of the nineteen people developed the disease -- until that August. Then seven people got yellow fever.