Kennaway, discussing the effect of _muscular exercise_ on the excretion of endogenous purins, noted that during unaccustomed exercise the _uric acid output_ of the kidneys diminished, but that of the purin bases is relatively augmented, but, on the whole, he found that the total purin output (bases plus uric acid) was not very much increased. Leathes and others, investigating the effects on uric acid excretion of strenuous exercise, established the occurrence of a distinct increase. Given that the same kind of exercise is practised on the day following, the said increase is much less marked. If, however, some different form of muscular activity is undertaken, another increase in uric acid follows. It would appear, therefore, that, despite conflicting evidence, the balance of opinion favours the view that muscular activity does lead to increase in endogenous uric acid excretion. (_b_) _Periodic Variations._—Leathes noted _diurnal_ and _nocturnal_ variations in the excretion of endogenous uric acid, the maximum occurring within the early waking hours, and sinking to a minimum towards the evening. His experiments, he held, indicated a variation in the actual formation of endogenous uric acid at different periods of the day. Rockwood also found that an increase occurred during the daytime, and Pfeil, that there was a morning rise in the amount of uric acid passed. The fact that doubt still obtains as to whether muscular exercise has any effect on endogenous uric acid excretion, renders explanation of this diurnal variation difficult. This especially as there are no fluctuations in the urinary functions that could in any way account for it. PATHOLOGICAL STATES Endogenous uric acid is increased under certain pathological conditions. Leathes’ recent work confirmed the view that there is an increased production of nitrogenous waste in _fevers_. After taking a large dose of anti-typhoid serum his temperature rose to 103° F. Experimenting on himself, he found his output of urea, uric acid, and creatinine all increased, but of all three _uric acid_ showed the most marked alteration. The question now arises as to whether such is due to increased production or diminished destruction. Some further experiments conducted by Leathes on himself may serve to elucidate this point. Subjecting himself for a prolonged period to cold baths, a similar increase in his _uric acid_ output ensued. This would appear to indicate that, through increased loss of heat, the bodily processes of combustion were augmented to maintain the body temperature, with, as a consequence, increased uric acid excretion.