On the other hand, Wells, discussing the destruction of uric acid, observes that repeated investigations show “that the tissues of man have no power whatever to destroy uric acid _in vitro_; the earlier reports of positive uricolysis undoubtedly being erroneous.” His final conclusion, after weighing all available evidence, is that it is highly probable that in man “most of the purin absorbed from the food, and practically all the purin from cell metabolism, is converted into uric acid and excreted as such.” MacLeod, however, reflecting on the fact that uric acid is not destroyed when extracts of the organs are incubated at body temperature with uric acid or its precursors, bids us bear in mind that, “although the uric acid is thus shown not to be destroyed _in vitro_, it may nevertheless be destroyed in the living animal.” We see, therefore, that the question, Whether uric acid can undergo destruction in the human body? is still a matter of dispute, and must, pending further investigation, remain _sub judice_. Still, despite the conflict of evidence, clinicians have felt justified in assuming that one of the factors in the genesis of gout may be an entire _absence_ or a _diminution_ in the amount or activity of this _uricolytic ferment_. But the awkward fact remains that all researches up to date have failed to establish the presence in the human body of any enzyme which can decompose uric acid. Should, therefore, future investigators place beyond the reach of cavil the claim that no _uric-acid-destroying enzyme exists in the body_, it would seem that, _ipso facto_, man, through lack of this capacity for rapid oxidation of uric acid, is, by this same disability, rendered a potential victim of _uric acid retention_ and _deposition_. Elucidation of this vexed point seems more probable in view of the striking discovery recently made by R. Benedict, viz., that in one particular breed of dog, the Dalmatian, _uricase_ is wholly absent. In respect of this _lack of a uric-acid-destroying ferment_, the Dalmatian breed of dog has a _purin_ metabolism apparently identical with that of man.[16] Thus, if fed on a purin-free diet, he passes large quantities of uric acid, and if the latter be injected subcutaneously, elimination in quantity as such ensues; this, in striking contrast to what obtains in all other animals in whom, as before noted, uric acid is mostly oxidised to _allantoin_ before excretion. Now, as MacLeod observes, investigation into the metabolism of nucleic acid has, in man, been hampered greatly, in that the absence of uricase from his tissues, prior to Benedict’s discovery, rendered experimental researches on the lower animals valueless. But, in light of the above revelation later by R. Benedict, it may reasonably be hoped that in the near future our knowledge as to the location and nature of the intermediary chemical processes occurring in the metabolism of nucleic acids may be materially clarified. CHAPTER IX