In Mr. John Bach McMaster’s “History of the People of the United States,” is a narrative of the terrible yellow-fever epidemic which occurred in Philadelphia in the year 1793, causing the death of over four thousand people in four months. In those days men had strange ideas as to the causes of yellow fever; they believed, in this case, that it “had come from a pile of stinking hides that had been on one of the wharves.” The historian goes on to describe the strange expedients they adopted to get rid of it. “People were bidden to keep out of the sun, and not to get tired. The doctors had little faith in bonfires as purifiers of the air, but much in the burning of gunpowder. Every one then who could buy or borrow a gun, loaded and fired it from morning till night. Then one remedy after another would be suggested, and people would cover themselves with it—nitre, tobacco, and garlic, mud-baths, camphor, and thieves’ vinegar. The last could only be procured by going to the shop. The purchaser going to get it was careful to have a piece of tarred rope wet with camphor at his nose, and in his pocket his handkerchief soaked with the last preventive he had heard of. He shunned the footpaths, fled down the nearest alley at sight of a carriage, and would go six blocks to avoid passing a house where a dead body had been taken out a week before. He would not enter a shop where another man stood at the counter; he would rush in, throw down the money, and rush home—soak everything in this prepared vinegar, and live on a prescribed diet, water-gruel, oatmeal, tea, barley-water, or a vile concoction called apple-tea. If his head pained him or his tongue felt rough, he would immediately wash out his mouth with warm water and honey and vinegar——” etc., etc. At the time when I read all this, it made a peculiar impression upon me, because the newspapers happened just then to be full of the discovery of the true cause of yellow fever. And so all the time that I was reading about the man with the tarred rope in his hands and a sponge wet with camphor at his nose, I had this thought in my mind: And while he was waiting outside of the shop, a mosquito flew up, all unheeded, and bit him. And so he died! It seemed to me a peculiarly neat illustration of the precise difference between knowledge and ignorance. It led me to reflect how very eager men ought to be to possess the former; and I put the anecdote away in my mind, thinking, “I shall use it some day when I want—all of a sudden—to scare someone out of a prejudice!”