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Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.
Hypertension is a silent killer because it is deadly and has no significant early symptoms. The danger from hypertension is the extra load on the heart, which can lead to hypertensive heart disease and kidney damage. This occurs without any major symptoms until the high blood pressure becomes extreme. Regular blood pressure checks are an important method of catching hypertension before it can kill you.
Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.
![Inflammation. Inflammation is characterized by the presence of swelling, redness, heat, and pain. Sw](https://biology-forums.com/gallery/47/medium_14755_11_11_12_7_18_45_10040570.jpeg)
![Immunization with a vaccine. A healthcare professional is injecting a vaccine into the patient’s arm](https://biology-forums.com/gallery/47/medium_14755_11_11_12_7_20_13_10048217.jpeg)