Pratt, working in Folin’s laboratory, investigated a series of cases of gout, selecting only those in which (1) Tophi were found, (2) A history of characteristic attacks of acute gout was obtained, or (3) Typical symptoms developed while under observation. At the time of examination the average uric acid content, irrespective of the diet or condition, was 3·7 mg. In three patients on _ordinary diet_, who were seen during attacks, the amounts were 4·5, 4·8 and 5·7 mg. of uric acid. In two other patients, also seen during attacks, and while on a _purin-free_ diet, the uric acid in four estimates ranged from 2·4-5·1 mg., viz., an average of 3·6 mg. None of these patients were taking atophan. Seven patients, on a _mixed_ diet, and free at the time from symptoms of gout, contained on the average 4·3 mg. of uric acid in their blood. On the other hand, examination of the blood in six patients on a _purin-free_ diet, at the time manifesting no acute symptoms of gout, revealed an average uric acid content of 3 mg. From the foregoing considerations it may be deduced that:— (1) In gout there is a condition not of uricæmia, but of _hyper-uricæmia_. (2) That on the average the blood in _gouty_ subjects contains twice as much uric acid as that of _non-gouty_ subjects, as evidenced by comparison of the average uric acid content of the blood in Pratt’s series of gouty cases (4·5 mg.) with Adler and Ragle’s non-gouty examples (1·7 mg.). (3) In contrast with non-gouty subjects, the uric acid content of the blood in _gouty_ subjects is augmented on a purin-rich diet. (4) Both in the inter-paroxysmal periods and during attacks the uric acid content of the blood, when on a _mixed_ diet, is higher than when on a purin-free diet. HYPER-URICÆMIA IN NON-GOUTY ARTHRITIS Pratt, of Boston, has found that a condition of hyper-uricæmia is sometimes demonstrable in joint disorders other than gouty; but he maintains that the following distinction obtains, viz., that while in gout the hyper-uricæmia is generally _constant_, in other forms of arthritis it appears to be _transient_. He cites a case of _infective_ arthritis, not exhibiting the clinical features of gout, in which the first analysis of the blood by Denis revealed a uric acid content of 7·6 mg.; but on a subsequent examination, seven months later, only 0·8 mg. was found, this, though the patient at the time was on a _purin-rich_ diet. This difference is response to exogenous purins in gouty, as opposed to _non-gouty_ arthritics, is well illustrated in the following table. According to Walker Hall, the following example illustrates the effect of purin-free as opposed to purin diet on the uric acid blood content in a gouty subject:—