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
URIC ACID IN RELATION TO GOUT
It will be recalled that at the close of our chapter on Pathogenesis we referred to the growing scepticism of Garrod’s views as to the pathogeny of gout. Still, if we except Edward Liveing’s pertinent observation that uricæmia was not peculiar to gout, naught, save alternative hypotheses, unsupported by pathological data, was advanced. Consequently, Garrod’s facts never being seriously called in question, his position remained unassailable, until, in the year 1898, his original observations as to the lowered alkalinity of the blood in acute gout, and the increased uric acid content thereof during the same, were definitely contradicted by Magnus Levy.
Working with more modern and more reliable methods of technique, this observer, in a series of seventeen cases of acute gout, found no evidence of any lessening in alkalinity of the blood or of any augmentation of its uric acid content as compared with the inter-paroxysmal period.
Again, as to Garrod’s claim that there was a diminished excretion of uric acid during the attack, this also, while supported by Minkowski, was called in question by Pfeiffer, Levy, and Badt, who found the reverse to be the case, i.e., a notable increase in the excretion of uric acid during the paroxysm.
These results were again in 1900 confirmed by Chalmers Watson. An exhaustive study of a series of cases of acute gouty polyarthritis convinced him that:—