It were well in approaching any acute polyarthritis of obscure nature to bear in mind the axiom that _any or all infections may be complicated by arthropathies_, also that if the said polyarthritis does not respond quickly to colchicum or salicylate of soda we are almost certainly dealing with an infective arthritis either of specific or undifferentiated type. The _specific_ forms of infective arthritis, as far as seems necessary, have been dealt with, but those rarer forms not referred to, viz., _influenzal_, _pneumococcal_, _dysenteric_, _meningococcal_, etc., have also to be borne in mind, if the history reveal any recent occurrence of these disorders. Still far more common than any of these are the _acute infective arthritides_ of _undifferentiated_ type. As we before remarked, an extraordinary general clinical resemblance obtains between these types of joint disorder and _acute gouty polyarthritis_. Indeed, _in the absence of tophi_, their differentiation is well-nigh impossible. Even the blood picture in both types of the disorder is strikingly similar in the matter of _leucocytosis_ and _secondary anæmia_. Recently Dr. Henry A. Christian, lecturing at a clinic of the Harvard Medical School, emphasised this clinical similarity and the difficulty of discriminating between these two types of joint disorder. As he rightly says, “while there is a definite _acute gouty polyarthritis_ (as evidenced by external tophi or deposits in bone or cartilage with variations in uric acid output) and also an equally definite _infective arthritis_, yet between those two there is a very considerable number of cases that present some of the factors suggestive of _gout_ and other factors suggestive of an _infectious arthritis_, and there is where the difficulty comes.” This is precisely the state of affairs, and one may well ask where _gout_ ends and _infection_ begins. Let us take an example. A man exhibiting _tophi_, the subject also of _pyorrhœa alveolaris_, develops an _acute polyarthritis_. What then is the nature of the joint disorder? There is a gouty element in his case, as attested by _tophi_, also an infective element, as evidenced by _oral sepsis_. Now are we to regard such a case as one of _infective arthritis_ of _undifferentiated_ type occurring in a _gouty_ subject, or are we to proceed on the assumption that the presence of _tophi_ negatives the possibility of infection and forthwith to class it as a case of _acute gouty polyarthritis_ of so-called _metabolic_ origin?