Quinine is one of the most important of the group of compounds known as the alkaloids. It occurs largely together with an allied alkaloid known as cinchonine in cinchona bark. It is found in the greatest quantity - 2 or 3 per cent. - in the variety known as yellow bark, Cinchona calisaya, and may be extracted by suitable solvents. The exact methods of extraction and details of process by which the compounds are commercially obtained are kept to an extent as trade secrets. Quinine in its chemical deportment behaves as a basic substance, uniting with acids to form salts. Of these, sulphate of quinine is that which is commonly used, and the form in which quinine is almost universally used. The alkaloid itself crystallises in needle-shaped crystals, melting about 147° and possessing a bitter taste. The sulphate forms shining needle-like crystals slightly soluble in cold water and more easily in hot. It dissolves readily in dilute sulphuric acid, and the solution is distinguished by being fluorescent, having a fine blue fluorescent tint. Quinine can be readily detected by the beautiful green coloration produced when chlorine water, followed by ammonia, is added to the compound or its solution. Its chemical constitution is not yet satisfactorily determined, but it appears to be a quinoline derivative. The sulphate of quinine is often given in one-grain doses as a tonic, and in larger doses in fevers or malaria. It is liable when administered in large doses to produce headache, deafness, singing in the ears, and other symptoms; to this condition the term "Cinchonism" is applied.