The severity of Mercury's effect on human health depends on the following things: the chemical form, duration, and dosage of the Mercury, and the age and overall health of the exposed person. There are three chemical forms of Mercury: Methyl-, Elemental, and compound Mercury. Each has their own symptoms of poisoning. Methylmercury (absorbed through ingestion of food items containing Mercury) mostly causes vision and speech impairment, unusual sensations, lack of balance/coordination, and muscle weakness. Elemental Mercury causes effects (through vapor absorption in the lungs) such as tremors, emotional swings, insomnia, and neuromuscular changes. Other mercury compounds (both organic and inorganic) often cause damage to the gastrointestinal tract (where it is absorbed), the kidneys, and the nervous system.