XANTHINE, or XANTHIC OXIDE (CloH4N40,), was first described by Dr. Marcet, who regarded it as a very rare constituent of urinary calculi, and from its composition he gave it the name of uric oxide. During the last ten years it has been proved to be a normal ingredient (although to a very small amount) of human urine, and has been found in the brain, the spleen, the pancreas, and the liver of the ox; in the thymus gland of the calf: and in the muscular tissue of the horse, the ox, and of fishes; as well as in the liver of various animals. Calculi composed of this substance are extremely rare, the total known number obtained from the human subject being less than half a dozen. They are of a light-brown cinnamon color, assume a waxy appearance when rubbed, and consist of concentric layers easily separable from one another. Xanthine occurs in such very minute quantities in the various tissues, and is so rare an ingredient of calculi, that it is unnecessary for us to enter into any description of its properties, further than to state that, when dried, it exists as a yellowish-white powder, which assumes a glistening appearance when rubbed, and exhibits no signs of crystallization under the microscope; moreover, the chemical difficulties of detecting traces of this substance are so great that we shall not attempt to describe its tests. It seems to be intermediate to uric acid and
hypoxanthine, both in a chemical and a physiological point of view. The composition of uric acid is represented by the formula 01.114S40e, that of xanthine by C1oH4N404. and that of hypoxanthine by C.H.N40,. The former two occur simultaneously, not only in the urine, but in the spleen, the liver, and the brain; while xanthine is not only invariably accompanied by larger or smaller quantities of hypoxanthine, but the latter can be made by the oxidizing action of nitric acid to yield a product from which xan thine (in place of hypoxanthine) may be obtained by a process of reduction. Xanthine must be regarded na higher stage of oxidation of hypoxanthine. and a product of the regressive metamorphosis of the tissues, which, in the ordinary condition of the system, is excreted in a more highly oxidized form of urea, uric acid, etc.
This substance is staked to have been found by Gael in some oriental bezoars extracted from the intestines of certain ruminating animals. It is most probable that the supposed bezoars were in reality urinary calculi.