A fourth class of the preventives of malignant fevers are certain substances which are said to destroy miasmata by entering into mixture with them. Two persons, who were very much exposed to the causes of the fever in 1798, took each of them a table spoonful of sweet oil every morning. They both escaped the fever. Did the oil, in these cases, act by destroying miasmata in the stomach chemically? or did it defend the stomach mechanically from their action? or did it prevent the disease, only by gently opening the bowels? It is certain the fat of pork meat protects the men who work in the lead-mines of Great-Britain from the deleterious effects which the fumes of that metal are apt to bring upon the stomach and bowels, and that a poisoned arrow, discharged into the side of a hog, will not injure him, if it be arrested by the fat which lines that part of his body. The vapour which issues from fresh earth has been supposed to destroy the miasmata which produce malignant fevers, by entering into mixture with them. Most of the men who were employed in digging graves and cellars, and in removing the dirt from the streets of Philadelphia, in 1793, escaped the fever of that year. In the new settlements of our country, it is said, the poison of the rattlesnake is deprived of its deadly effects upon the body, by thrusting the wounded limb into a hole, recently made in the earth. The fable of Anteus, who rose with renewed strength from the ground after repeated falls, was probably intended to signify, among other things, the salutary virtues which are contained in the effluvia which issue from fresh clods of earth. 3. There are many facts which show the efficacy of the volatile alkali in destroying, by mixture, the poison of snakes. One of them was lately communicated to the public by Dr. Ramsay, of South-Carolina. What would be the effect of the daily use of a few tea spoonfuls of this medicine in a liquid form, and of frequently washing the body with it, during the prevalence of pestilential epidemics? The miasmata which produce malignant fevers often exist in an inoffensive state in the body, for weeks, and perhaps months, without doing any harm. With but a few exceptions, they seldom induce a disease without the reinforcement of an exciting cause. In vain, therefore, shall we use all the preventives that have been recommended, without, V. Avoiding of all its exciting causes. These are,