Guanin

Guanin is a yellowish-white, amorphous substance, which derives its name from its being a constituent of guano; but it also forms the chief constituent of the excrement of spiders, has been found attached to the scales of fishes—the bleak, for example—and seems to be a normal constituent of the mammalian liver and pancreas. With regard to its occurrence in guano, as it has not been found in the recent excrement of seabirds, there is every reason to believe that it is formed by slow oxidation (from atmospheric action) of the uric acid, much as uric acid can be made to yield urea and oxalic acid. And in the pancreas and liver it probably represents one of those transitory stages of disintegrated nitrogenous tissue which are finally excreted by the kidneys in the more highly oxidised form of urea. Guanin is a diacid base, but also forms salts with metals, and combines with salts. When heated with hydrochloric acid and potassium chlorate, it is oxidised to carbon dioxide, guanidin, and parabanic acid.