Cod-liver oil from various kinds of fish has been used since time immemorial (sometimes involuntarily) to increase resistance to winter's afflictions with its high vitamin content. In addition, special elements have been discovered in shark cod-liver oil (shark liver oil): the alkylglycerols. Alkylglycerols are also found in the oil of the rabbit fish (Chimaera Monstrosa), a particular deep-water shark, whose cod-liver oil is especially rich in alkylglycerols and almost 2,5 times as plentiful as that of the ordinary shark. Alkylglycerols close the gaps in our defence mechanism. They stimulate the production of antibodies (subtances that intervene in common immune responses) and the activity of the white blood cells. They also contribute their part to controlling and destroying ageing cells, which can invade some tissues.