Copper is present in very small amounts in the human body and cannot be detected by normal histologic methods. There is more copper in the liver, and when hepatomegaly or cirrhosis occurs, the copper content increases significantly. The principle of the erythrocyanine method lies in the reaction between erythrocyanine and copper salts to produce an erythrocyanine-diimine (ethylenediamine disulfide erythrocyanine)-type precipitate of copper salts, which is blackish-green in color.