The job: Homeopathy is a system of medicine, founded by German doctor Samuel Hahnemann, at the turn of the 19th century and reached the height of its popularity in the U.S. in the early part of the 20th century. It was based on the idea of treating "like with like." Homeopathists (or homeopaths) treated patients by administering small doses of substances that would in large doses cause symptoms similar to the disease or ailment. For example, small doses of caffeine might be used to treat insomnia or restlessness.

Killed by: Increased standards in U.S. medical education. In 1908, a government study found the quality of American medical schools lacking. And a subsequent report called for stricter admission and graduation requirments. Medical schools across the country, many of them homeopathic, closed as a result. Today, homeopathy remains popular in other parts of the world, including the U.K. and France, and a small number of homeopaths continue to practice in the U.S.