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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
ACTH levels are normally highest in the early morning (between 6 and 8 A.M.) and lowest in the evening (between 6 and 11 P.M.). Therefore, a doctor who suspects abnormal levels looks for low ACTH in the morning and high ACTH in the evening.
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.
The first documented use of surgical anesthesia in the United States was in Connecticut in 1844.
There are 60,000 miles of blood vessels in every adult human.