I had given my landlady particular instructions about not handling the various things in my laboratory. I strictly enjoined her not to touch anything under any circumstances--I would keep the place in order myself. Nevertheless, she could not be prevented from entering the laboratory to dust and tidy it up a bit, and she generally knocked over a thing or two in the process. One day, I brought home a pint glass jar of pure nitroglycerin, setting it up out of reach of the little three-year-old girl, who often used the laboratory as a playground, in spite of my protestations. I called my landlady's attention to the fact that this bottle contained nitroglycerin, and I explained its dangerous character unless it were left undisturbed. I told her that, if she found it out of the question to let the bottle alone, and should, in dusting, succeed in knocking it over and spilling its contents upon the table where it stood or upon the floor, and should wipe up the oily liquid with a rag, not to put the rag in the stove, for, if she did, she would blow the roof of the house off, and project herself into the empyrean, and through it and out at the other side. She actually remembered this injunction for more than three days, but, on the fourth day, on my return home, the little three-year-old met me as I came in, and said: "Mamma very sick. Cure Mamma." "Mamma" was lying upon a sofa, pale as a ghost, and breathing heavily. When I asked her what the matter was, she answered, "Oh, I am so sick!" I began to be thoroughly frightened, and wormed out of her the fact that she had a terrible nitroglycerin headache. It came out that she had been dusting and tidying the laboratory that day, and had inadvertently knocked over the bottle of nitroglycerin. Fortunately, it did not explode as it fell, the contents being merely spilled upon the table and floor. She took an old towel and soaked the liquid up with it. She then rolled up the towel in a tight, snug, compact wad, and started toward the kitchen to put the wad in the cook-stove and burn it up, when, just as she arrived at the stove, she felt a dizziness in the head, and a strange sort of sinking sensation in the stomach. The top of her head began to buzz and pound. Then, she saw light. It dawned upon her, like the inspiring flash that came upon Saul, that this was nitroglycerin, and she recalled what I had told her about the effect it would have upon her if she handled it, and my direction that, if she should spill the stuff and then wipe it up, she must not burn the rag. THE FATAL HAT Out in the Pennsylvania oil regions in the early days, while nitroglycerin in the liquid state was being used experimentally as a blasting agent, some boys found in a creek an old felt hat, which had been used as a filter for nitroglycerin.