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Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
Vaccines prevent between 2.5 and 4 million deaths every year.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
The first oncogene was discovered in 1970 and was termed SRC (pronounced "SARK").

