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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.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Patients who have undergone chemotherapy for the treatment of cancer often complain of a lack of mental focus; memory loss; and a general diminution in abilities such as multitasking, attention span, and general mental agility.
Cocaine was isolated in 1860 and first used as a local anesthetic in 1884. Its first clinical use was by Sigmund Freud to wean a patient from morphine addiction. The fictional character Sherlock Holmes was supposed to be addicted to cocaine by injection.
In ancient Rome, many of the richer people in the population had lead-induced gout. The reason for this is unclear. Lead poisoning has also been linked to madness.