To have any semblance of diagnostic value, the patient should be on a _purin-free_ diet, and a long series of exact quantitative examinations made. C. v. Noorden, to gauge the limit of tolerance of his patients, gives them increasing amounts of purin, and so determines the quantity the subject can deal with without showing retention. But, as Von Fürth satirically observes, “when a physician allows a quantitative analysis to be made of any arbitrarily collected specimen of urine of his patient and then makes a diagnosis of the presence or absence of a ‘gouty diathesis’ after a glance at the list of data of the analysis, he is really not proving by his actions his possession of diagnostic acumen as much as he is laying bare his total ignorance of bio-chemical matters.” So much for the diagnostic valency of uric acid estimates in chronic gout, but if the patient be on purin-free diet, and an acute attack ensue, the curve of uric acid excretion is fairly characteristic. In other words, for a day or two preceding the outbreak, the uric acid output falls below the usual level, but early in the attack rises markedly, to be followed by a secondary fall. Some aid in diagnosis has been afforded by the fact that after ingestion of purin-containing food the gouty individual does not, like a normal person, eliminate the excess of uric acid, but the excretion is “spread out over a number of days.” But this retardation and diminution in the excretion of exogenous purins has been seen in non-gouty forms of arthritis, not to mention some cases of nephritis and chronic alcoholism. Hence delayed nuclein exchange, though highly suggestive of gout, is not infallibly diagnostic thereof. _As to uric acid in the blood_, it will, I fear, not for long, if ever, be easy to prevail on patients to submit to withdrawal of the amount of blood necessary, even by modern methods, for its estimation. Fortunately, our American _confrères_ appear to be more successful in securing such opportunities. Pratt states that in his twenty-one cases of genuine gout the uric acid content of the blood, irrespective of diet, was 3·7 mg. per 100 grams, as opposed to 1·7 mg., the average amount in 156 non-gouty cases studied by Adler and Ragle. Still Pratt noted that in a few cases of undoubted gout the uric acid content of the blood was within normal limits, though it never fell, even on a purin-free diet, below 1·4 mg. Nevertheless he holds that there is conclusive evidence that the uric acid content of the blood is in gouty individuals notably increased both in the intervals and during attacks.