C₅H₅N₅ + H₂O = C₅H₄N₄O + NH₃; C₅H₅N₅O + H₂O = C₅H₄N₄O₂ + NH₃ Adenine. Hypoxanthine. Guanine. Xanthine. By the action of oxidases also present in the tissues hypoxanthine is changed into xanthine and xanthine into uric acid (trioxy-purine), this by a specific ferment xanthine oxidase. C₅H₄N₄O O—C₅H₅N₄O₂; C₅H₅N₄O₂ O C₅H₄N₄O₃ Hypoxanthine. Xanthine. Xanthine. Uric acid. [Illustration: SCHEME ILLUSTRATING THE PROBABLE STAGES IN THE PASSAGE OF PURIN THROUGH THE BODY (WALKER HALL)] It will be seen that the disintegration of nucleic acid involves many stages, and its complexity is such that we make no apology for drawing upon the masterly monograph of Walter Jones for further elucidation of this intricate question. In relating the history of nucleic acid in the animal body Jones has found it convenient to introduce certain terms wherewith to designate the various elements of the _nucleic acid molecule_. Thus, the molecule in its entirety is termed a _tetra-nucleotide_. The cleavage of this complex is initiated by the action of two specific enzymes. Through their agency the tetra-nucleotide is first cloven into two _di-nucleotides_, which immediately divide up into four _mono-nucleotides_. These ferments are:— (1) _Phospho-nuclease_ (which splits off the phosphoric acid radicle, leaving a nucleoside, guanosine or adenosine). H₂PO₄—C₅H₈O₃—C₅H₄N₅O + H₂O----->H₃PO₄ + C₅H₉O₄—C₅H₄N₅O Guanylic acid. Phospho-nuclease. Guanosine. (2) _Purin-nuclease_ (which splits off the purin radicle, viz., separates out both phosphoric acid and carbohydrate groups, leaving free purin bases). H₂PO₄—C₅H₈O₃—C₅H₄N₅O + H₂O----->H₂PO₄—C₅H₉O₄ + C₅H₅N₅O Guanylic acid. Purin-nuclease. Guanine. Now, in sequence to either of the foregoing cleavages by the phospho- or purin-nucleases another set of enzymes come into the field. Under their _deaminising_ effect the amino group is abstracted, with the formation of either free _oxy-purins_ or oxy-purins still bound in glucoside-like combination with sugar. If the oxy-purins are free, the following is the reaction:— C₅H₅N₅O + H₂O------>C₅H₄N₄O₂ + NH₃ Guanine. Guanase. Xanthine. Should, however, the guanine glucoside be present:— C₅H₉O₄—C₅H₄N₅O + H₂O------>C₅H₉O₄—C₅H₃N₄O₂ + NH₃ Guanosine. Guanosine-deaminase. Xanthosine. In the latter instance a hydrolysing enzyme, _xanthosine-hydrolase_, by its action, splits off xanthine. We see, therefore, that by either route the end-product is the same. Following a like series of changes, the adenine radicle is transmuted into hypoxanthine. This either directly by the action of adenase:— C₅H₅N₅ + H₂O------>C₅H₄N₄O + NH₃ Adenine. Adenase. Hypoxanthine. or indirectly through the agency of adenosine-deaminase, the hypoxanthine-glucoside (inosine) is formed, and subsequently the hypoxanthine is split off.