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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.
The B-complex vitamins and vitamin C are not stored in the body and must be replaced each day.
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.
Interferon was scarce and expensive until 1980, when the interferon gene was inserted into bacteria using recombinant DNA technology, allowing for mass cultivation and purification from bacterial cultures.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.