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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.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
The word drug comes from the Dutch word droog (meaning "dry"). For centuries, most drugs came from dried plants, hence the name.
Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.