Cholesterol a complex fatty alcohol, is essential for the proper working of the digestive and nervous systems. It is present in foods of animal origin, large amounts being found in egg yolk. Cholesterol is insoluble in water. In the body of a man or an animal; it is carried around by two types of proteins, low density lipoproteins (LDL) and high density lipoproteins (HDL). LDL is notorious as a contributory cause of atherosclerosis—clogging of the arteries with fatty deposits of pure cholesterol as well as gallstones. HDL, in contrast, is wholly beneficial and helps to keep the arteries clear. But it should be noted that some LDL is necessary; it is only harmful in excess.