On the other hand, _guanase_, also a deaminising enzyme, is in man to be detected in the _kidney_, _lung_, and _liver_, but not in the pancreas or spleen. In the pig, however, guanase is lacking, and its absence no doubt explains why deposits of guanine may occur in the muscles constituting the so-called _guanine gout_ met with in swine. It is worthy of note also that in pigs’ urine the content of purin bases exceeds that of uric acid. To sum up, in man the enzyme, _xanthine-oxidase_, which forms uric acid from xanthine, is located chiefly or exclusively in the _liver_. This, of course, represents the _final_ stage of purin metabolism, but the antecedent chemical processes involved in the disruption of nucleic acids are initiated by the action of enzymes in the _intestinal juices_ and _wall_, and to a consideration _seriatim_ of these changes we now proceed. STAGES IN DISRUPTION OF NUCLEIC ACID As might be expected from the complex structure of the nucleic acid molecule, a number of ferments are concerned in its disruption. The gastric and pancreatic juices contain not a trace of any enzymes. Thus, when _nucleo-protein_ is subjected to the gastric juice a moiety of protein is readily split off and hydrolysed to peptone and other products of proteolysis. But the nuclein element remains unacted upon until it comes under the action of the pancreatic juice. Hydrolysis then ensues, and the ingested nuclein is broken down into nucleic acid and protein. The _nucleic acid_ remains unaffected by the pancreatic juice, but, coming in contact with the _succus entericus_, it undergoes partial decomposition through the action of a ferment called nuclease or _nucleic_-acidase. Under its disruptive effect the nucleic acids or _poly-nucleotides_ are further split up into groups known as _nucleotides_. The two _pyrimidine_ nucleotides split off and undergo no further change. But, through the action of another ferment, _nucleotidase_, the _purin_ nucleotides are further decomposed to yield _nucleosides_ (substances of the glucoside class made up of a combination of a purin base with a carbohydrate group of the nucleic acid with which also phosphoric acid is linked). No further stage in hydrolysis of nucleic acid occurs in the intestine, but the _nucleosides_ are again in turn split up after reaching the tissues, particularly in the _spleen_, _liver_, and _thymus_. This, under the action of specific enzymes, _nucleosidases_, which succeed in breaking the nucleosides down into the so-called “building stones” of the _nucleic acid molecule_, phosphoric acid group, carbohydrate group, pyrimidine and purin bases, especially adenine and guanine. The adenine and guanine thus formed are, by the action of the ferments _adenase_ and _guanase_, converted and, by the removal of their amino group, transformed, adenine into hypoxanthine, and guanine into xanthine, thus:—