But, although it is necessary to say little with regard to temperaments obviously distinguishable; yet it is well known, that very great varieties in the operation of mercury arise from peculiarities in constitution. And this happens where there are no particular marks indicating such a singularity. Some constitutions are affected by mercury with very great ease, whether as acting on the alimentary canal, or as entering the system, and exerting its effects there. In cases, therefore, where the constitution of the patient is not previously known, some degree of preference is, on this account, due to the mildest forms. And, in those cases for which the more acrid ones seem best fitted, it is necessary to begin with the employment of small doses; and, if the action of these shall be found to be too violent, to have recourse to the different means of taking off sensibility. The most immediate, and perhaps the most effectual, means of removing or diminishing sensibility, is by the use of opium. But the same end may, in many cases, be obtained with equal ease, and less hazard, from the use of emollient and mild diluents; such as decoctions and emulsions, abounding with vegetable mucilage. While some constitutions are easily affected by mercury, others, on the contrary, are acted upon with difficulty only. With these last, after the use of even a very considerable quantity of mercury, little, or perhaps no obvious action on the system can be observed. This is to be ascribed to one of two causes; either it arises from the mercury’s never having entered the system; or from its being accumulated there without proving a stimulus to any secretion. In the latter of these cases, all the effects wanted from the use of mercury may be obtained with greater ease than in any other. The only thing, then, which is necessary in such cases is to proceed with caution, and not to throw into the system an unnecessary quantity of mercury, by which the patient may be exposed to those inconveniencies which, in a greater or less degree, accompany every increased excretion. But it is not always an easy matter to distinguish betwixt this and the case first mentioned, in which it was alledged, that the want of obvious action arose from the mercury’s not having entered the system. When this happens, a gradual and slow procedure would not only be losing time to the patient, but allowing the disease to gain ground. The only certain mark for distinguishing betwixt these two cases, is the change produced in the morbid symptoms. In the one, the disease remains either unaltered or increased; in the other, all the symptoms are manifestly changed for the better.