At the same institution in Boston, Adler and Ragle conducted a similar series of investigations, though on a more extended scale. These observers, taking 156 unselected _psychopathic_ patients, found that in 107 examples the uric acid content of the blood was from 1-2 mg., in thirty-eight more than 2 mg., and in eleven instances less than 1 mg. To sum up, the uric acid content varied from 0·7-4·5 mg. per 100 grams of blood, an average of 1·7 mg. As before stated, it was until recently maintained that in the blood of _normal_ individuals, on a _purin-free_ diet, _uric acid_ was undemonstrable. But McLester, utilising Folin’s method, found uric acid in the blood of fifteen _healthy_ individuals, who had been on a _purin-free_ diet for at least three days, and this in amounts ranging from 0·5-2·9 mg. per 100 grams of blood, an average of 1·4, as contrasted with 1·7, the average amount in Adler and Ragle’s series. Pratt, discussing these findings, considers that the fact that the _average_ amounts approximate so nearly in the two series is worthy of emphasis. This especially as all McLester’s examples were young healthy adults on a _purin-free diet_, while the patients studied by Adler and Ragle were of all ages and on a _mixed_ diet.[21] EFFECT OF EXOGENOUS PURINES As we are aware, the amount of uric acid excreted in the _urine_ increases markedly on a _purin-rich diet_. But recent researches appear to raise doubts as to whether the uric acid content of the _blood_ rises correspondingly. Thus, according to Walker Hall, “a state of _uricæmia_ is said to exist if the amount of uric acid in the blood exceeds 0·8 mg. per 100 c.c.” The figure he considers is probably too low for, after an average meat breakfast, the blood uric acid rises to 1 or 2 mg. per 100 c.c. _in normal_ adults, or even higher after an excessive intake of _purin-rich_ foods. On the other hand, Denis, investigating the effect of ingested purin on the uric acid content of the blood, found that in _normal_ individuals _no increase in the circulating uric acid_ follows the intake; in other words, the kidney, in _normal_ persons, is quite capable of excreting any excess of uric acid presented to it, thereby keeping the uric acid of the blood at the same level as obtains when only the _endogenous_ moiety thereof has to be eliminated. Moreover, another factor, according to Folin and Denis, that operates in the same direction is the _binding capacity of the tissues for uric acid_. Pratt of Boston’s observations, too, appear to indicate “That the uric acid derived from exogenous purin does not accumulate in the blood unless there is a disturbance in the uric acid metabolism.” On the other hand, given damage to the _kidney_ (even when this has not progressed to the point when nitrogen retention is apparent, as shown by the non-protein nitrogen values), an accumulation of uric acid takes place in the blood after a short period of purin feeding.[22]