A third class of preventives of malignant fever, are such as excite a general action, more powerful than that which the miasmata are disposed to create in the system, or an action of a contrary nature. These are,
1. Onions and garlic. All those citizens who used these vegetables in their diet, escaped the yellow fever in 1793. The greater exemption of the natives of France from this disease, wherever they are exposed to it, than of the inhabitants of other European countries, has been ascribed in part to the liberal use of those condiments in their food. The Jews, it has been said, have often owed to them their preservation from the plagues which formerly prevailed in Europe. It is probable leeks and onions, which to this day form a material part of the diet of the inhabitants of Egypt, were cultivated and eaten originally as the means of obviating the plagues of that country. I have been at a loss to know why the Author of Nature, who has endowed these vegetables with so many excellent qualities for diet and medicine, should have accompanied them with such a disagreeable smell. Perhaps the reason was, kindly to force them into universal use; for it is remarkable their smell in the breath is imperceptible to those who use them.
2. Calomel, taken in such small doses as gently to affect the gums. It preserved most of the crew of a Russian ship at Plymouth, in the year 1777, from a fever generated by filth in her hold. In a letter which I received from Captain Thomas Truxton, in the year 1797, he informed me, that an old and respectable merchant at Batavia had assured him, he had been preserved in good health by calomel, taken in the way that has been mentioned, during the sickly seasons, for upwards of thirty years. The mortality of the fevers of that island may easily be conceived of, when I add, on the authority of a physician quoted in Sir George Staunton's Account of his Embassy to China, that one half of all new comers die there on the first year of their arrival.
Our principal dependence should be placed upon those two preventives under this head. There are several others which have been in common use, some of which I believe are hurtful, and the rest are of feeble, or doubtful efficacy. They are,
3. Wine and ardent spirits. They both prevent a malignant fever, only when they excite an action in the system above that which is ordinarily excited by the miasmata of the fever; but this cannot be done without producing intoxication, which, to be effectual, must be perpetual; for the weakness and excitability, which take place in the intervals of drunkenness, predispose to the disease. Agreeably to this remark, I observed three persons, who were constantly drunk, survive two of our most fatal epidemics, while all those persons who were alternately drunk and sober, rarely escaped an attack of the fever. In most of them, it terminated in death.
4. Tobacco. Many hundreds of the citizens of Philadelphia can witness, that no benefit was derived from this weed, in any of the ways in which it is commonly used, in the late epidemics of our city. Mr. Howard says it has no effect in preserving from the plague.
5. Camphor suspended in a bag round the neck, and rags wetted in vinegar, and applied to the nose. These means were in general use in the fever of 1793, in Philadelphia, but they afforded no protection from it. It is possible they had a contrary effect, by entangling, in their volatile particles, more of the miasmata of the fever, and thus increasing a predisposition to it.
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.