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Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
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.
Malaria was not eliminated in the United States until 1951. The term eliminated means that no new cases arise in a country for 3 years.