How Four Discoveries Changed Lives

Jonas Salk and the Polio Vaccine

An information text written for this worksheet. Polio is a disease caused by a virus. It can make muscles weak and sometimes leaves people unable to walk or to breathe on their own. In the early 1950s, polio struck tens of thousands of Americans every year, most of them children. Many families kept their children away from swimming pools and summer camps, afraid of catching it. Jonas Salk, an American doctor and scientist, made a vaccine to protect people from polio. In 1954, more than a million children took part in a test of the vaccine. In April 1955 the vaccine was announced as safe and effective. Salk did not patent it, so it could be made widely. Within a few years, polio cases in the United States fell sharply.

Cyrus McCormick and the Reaper

An information text written for this worksheet. In the early 1800s, farmers cut ripe wheat by hand with a curved blade called a sickle or a scythe. Wheat must be harvested quickly once it is ripe, so a farm family could only plant as much as they could cut in a few weeks. In 1831, Cyrus McCormick showed a reaper on his family's farm in Virginia. Jo Anderson, a man enslaved on the farm, helped with the work, but the records say little about what he did. Pulled by a horse, the machine cut the wheat as it moved across the field. With a reaper, a few workers could harvest far more wheat in a day than many workers could by hand. In 1847 McCormick opened a factory in Chicago, close to the prairie farms. Farmers on the wide prairies of the Midwest began to plant much bigger fields, and fewer people were needed for farm work.