An alkaloid is a nitrogenous organic molecule that has a pharmacological effect on humans and other animals. The name derives from the word alkaline; originally, the term was used to describe any nitrogen-containing base (an amine in modern terms). Alkaloids are found in plants (e.g., in potatoes and tomatoes), animals (e.g., in shellfish) and fungi (e.g., in mushrooms), and can be extracted from their sources by treatment with acids (usually hydrochloric acid or sulfuric acid, though organic acids such as maleic acid and citric acid are sometimes used).