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Certain chemicals, after ingestion, can be converted by the body into cyanide. Most of these chemicals have been removed from the market, but some old nail polish remover, solvents, and plastics manufacturing solutions can contain these substances.
Ether was used widely for surgeries but became less popular because of its flammability and its tendency to cause vomiting. In England, it was quickly replaced by chloroform, but this agent caused many deaths and lost popularity.
Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
About one in five American adults and teenagers have had a genital herpes infection—and most of them don't know it. People with genital herpes have at least twice the risk of becoming infected with HIV if exposed to it than those people who do not have genital herpes.