Now, as to the second regulating factor, the _retention capacity_ of the _tissues_ for _uric acid_, it may be said that the amount, in _normal_ subjects, would appear to be small. But Fine, it may be noted, found that the uric acid content in divers tissues was relatively proportionate to that of the blood, whether normal or increased in amount. But, to resume, Denis also demonstrated that the uric acid content of the blood in patients suffering from various _chronic diseases other than gout_ was also not increased on a purin-rich diet. To sum up, the researches of Denis would appear to indicate that:— (1) In _normal_ subjects _no increase_ in the _uric_ acid content of the _blood_ follows exogenous purin intake. (2) The uric acid content of the blood in patients suffering from chronic diseases, other than _gout_ or _renal_ disease, is similarly _not_ augmented on a _purin-rich_ diet. (3) The _uric acid content_ of the _blood_ is _increased_ more or less markedly, after a short period of purin feeding, in the presence of defective _renal elimination_. In amplification of the second of the foregoing postulates some observations by Pratt may be quoted. This authority is of opinion that the low amount of uric acid present in the blood of unselected _psychiatric_ patients on a mixed diet (Folin and Denis, Adler and Ragle) shows that a retention of uric acid in the blood in any considerable amount for twenty-four to twenty-eight hours rarely occurs. For, as he informs us, these patients at the Boston Psychopathic Hospital, when on ordinary diet, are eating purin-containing food daily, and they might take as much or more purin during the forty-eight hours preceding the blood analysis as is contained in a single sweetbread meal. Now, as Pratt argues, if the uric acid thus derived accumulated in the blood, the amount found would be considerably greater than that of individuals on a _purin-free_ diet. But, on the contrary, it transpires that the average amount of uric acid found by Adler and Ragle in the blood of patients on an ordinary diet was only 0·3 mg. more than that found by McLester in normal individuals on a _purine-free_ diet. The diagnostic significance of these observations will be better appreciated when we come to discuss the sequential increase of the uric acid content of the blood in _gouty_ subjects after the ingestion of purin-rich substances. URIC ACID CONTENT OF BLOOD IN GOUT Taking 1-3 mg. per 100 c.c. as the normal, the uric acid content of the blood, in typical cases of gout, according to MacLeod, rises to nearly 10 mg. Gudzent, from his studies, maintains that the blood, in almost all cases of gout, contains as much or even more _mono-sodium urate_ than it can hold in solution (1-8 mg.), in other words, it is in effect a supersaturated solution of the relatively insoluble _lactim_ urate.