Liver

The liver of mammals, fowl, and fish is commonly eaten as food by humans . Pork, lamb, veal, beef, chicken, goose, and cod livers are widely available from butchers and supermarkets while stingray and burbot livers are common in some European countries. Animal livers are rich in iron, copper, B vitamins and preformed vitamin A. Daily consumption of liver can be harmful; for instance, vitamin A toxicity has been proven to cause medical issues to babies born of pregnant mothers who consumed too much vitamin A. For the same reason, consuming the livers of some species like polar bears, dogs, or moose is unsafe. A single serving of beef liver exceeds the tolerable upper intake level of vitamin A. 100 g cod liver contains 5 mg of vitamin A and 100 μg of vitamin D. Liver contains large amounts of vitamin B12, and this was one of the factors that led to the discovery of the vitamin. From Middle English liver, from Old English lifer, from Proto-Germanic *librō, from Proto-Indo-European *leyp- "to smear, smudge, stick", from Proto-Indo-European *ley- "to be slimy, be sticky, glide". Cognate with Saterland Frisian Lieuwer "liver", West Frisian lever "liver", Dutch lever "liver", German Leber "liver", Danish, Norwegian and Swedish language lever "liver" the last three from Old Norse lifr "liver".

Source: Wikipedia