The way in which mercury prepares the body for the small-pox, seems to be by promoting the several excretions, particularly that by perspiration, which, by diminishing the quantity of the fluids, and weakening the tone of the solids, renders the system less liable to a plentiful eruption of the small-pox. But I object to the use of this medicine for the following reasons: 1. It effectually deprives us of all the benefits of the cool regimen; for mercury, we know, always _disposes_ the system to take cold. 2. All the good effects of mercury may be produced by PURGES, which do not subject the body to the above-mentioned inconvenience. The PURGES may be suited to the constitutions, and in some cases, even to the inclinations of our patients. I have seen jalap, rhubarb, senna, manna, aloes, soluble tartar, glauber and Epsom salts, and the butter-nut pill, all given with equal success. The quantity should be sufficient to procure three or four stools every day. A little magnesia should always be mixed with rhubarb and jalap in preparing children. It will be sufficient for the mothers and nurses of infants to conform strictly to the vegetable diet. I have never seen any advantages from giving them even a single dose of physic. It is hardly necessary to observe, that the quality, dose, and number of purges are to be determined by the age, sex, and habits of our patients. A constitution enfeebled by a previous disease forbids the use of purges, and requires medicines of a restorative kind. Patients afflicted with cutaneous diseases bear larger and more frequent doses of physic, than are indicated in more healthy subjects. In adult subjects of a plethoric habit, blood-letting is very useful on the third or fourth day after inoculation. We are not to suppose, that every fat person labours under a plethora. A moderate degree of fat is so far from rendering the disease more violent, especially in children, that I think I have generally found such subjects have the small-pox more favourably than others. Moderate exercise in the open air should be used during the preparation. But hard labour, and every thing that promotes sweat or fatigue, as also the extremes of heat and cold, should be avoided.