The efficiency of mercurial medication must depend in a great degree on the concentration of mercury in the body; this, in turn, depends on the balance between the absorption and excretion of the mercury; this, again, can be learned only through chemical analysis. The importance of such chemical studies is evident; but the difficulty of exact determination of small quantities of mercury in the excreta has naturally resulted in limiting these studies. There are only a few series of quantitative observations, each limited to a few cases, and usually confined to the urine. These are much more difficult to analyze, but they play a not inconsiderable part and, what is most serious, a variable part in the excretion. Moreover, some if not most of the analytic methods contained inherent faults, and it was difficult to judge how far these might have influenced the results. Although these results were not worthless,