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Pink eye is a term that refers to conjunctivitis, which is inflammation of the thin, clear membrane (conjunctiva) over the white part of the eye (sclera). It may be triggered by a virus, bacteria, or foreign body in the eye. Antibiotic eye drops alleviate bacterial conjunctivitis, and antihistamine allergy pills or eye drops help control allergic conjunctivitis symptoms.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
Although the Roman numeral for the number 4 has always been taught to have been "IV," according to historians, the ancient Romans probably used "IIII" most of the time. This is partially backed up by the fact that early grandfather clocks displayed IIII for the number 4 instead of IV. Early clockmakers apparently thought that the IIII balanced out the VIII (used for the number 8) on the clock face and that it just looked better.