Vanadium is a rare, soft and ductile, silver-grey metal. It has good resistance to corrosion by alkalis, sulfuric and hydrochloric acid. It oxidizes readily at about 933 K. Vanadium is found combined in certain minerals and is used mainly to produce certain alloys. In biology, a vanadium atom is an essential component of some enzymes, particularly the vanadium nitrogenase used by some nitrogen-fixing micro-organisms. Vanadium is essential to ascidians or sea squirts in vanadium chromagen proteins. The concentration of vanadium in their blood is more than 100 times higher than the concentration of vanadium in the seawater around them. Vanadium is one of the 26 elements commonly found in living things. Rats and chickens are also known to require vanadium in very small amounts and deficiencies result in reduced growth and impaired reproduction. The potential role of vanadium in human health is described as a building material of bones and teeth. Vanadium is present in a variety of foods including skim milk, lobster, vegetable oils, many vegetables, grains and cereals. Fruits, meats, fish, butter, and cheese are relatively poor sources of vanadium. The daily dietary intake in humans has been estimated to vary from 10 microg to 2 mg of elemental vanadium, depending on the environmental sources of this mineral in the air, water, and food of the particular region tested. In animals, vanadium has been shown essential (1-10 microg vanadium per gram of diet). There is only circumstantial evidence that vanadium is essential for humans. However, in doses ranging from 0.083 mmol/d to 0.42 mmol/d, vanadium has shown therapeutic potential in clinical studies with patients of both insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) type. Vanadium(IV) chloride VCl4 is a soluble form of vanadium that is commonly used in the laboratory. V(IV) is the reduced form of V(V), and commonly occurs after anaerobic respiration by dissimilatory metal reducing bacteria. VCl4 reacts violently with water.