Moreover, there is no oil or gas stove which ever burns perfectly all the time, either because there is too much gas or insufficient air. Oil and gas stoves sometimes give a partly yellow flame. You can cause them to give a yellow flame at any time by blowing air against them, and that yellow flame means imperfect combustion, and a probability of the deadly carbon monoxide. These facts are known to every chemist and to every student of hygiene, and the fact that civilized people continue to burn such oil and gas stoves in their homes and offices is simply one more proof that our civilization values human welfare and health at nothing whatever in comparison with profits. Not merely should you see that you have a continuous supply of fresh air in your home, but you should try to keep down dust in your home, and especially fine particles of lint. Once upon a time our ancestors were unable to make houses and floors tight, and so they put rugs on the floors and hung tapestries on the walls to keep out the wind. We civilized people are able to make both floors and walls absolutely tight, and yet we continue to use rugs and curtains, it being the first principle of our education that propriety requires us to continue to do the things which our ancestors did. I am unable to think of a more silly or stupid thing in the world than a rug or a curtain, but I have lived in the house with them all my life, because, alas, the ladies cannot be happy otherwise. They want their homes to be "pretty," and so they continue to set dust traps, and to set themselves futile jobs of house cleaning and shopping. Not all of us are able to be out of doors as much as we ought to be, but all of us spend seven or eight hours out of every twenty-four in sleep, and this time at least we ought to spend out of doors. I understand that this is futile advice to give to the very poor. I was poor myself for many years, and had to put all my clothes on at night in order to keep warm, and even then I could not always do it. Nevertheless, from the time I first realized the importance of ventilation I never slept in a room with a closed window. I say, sleep outdoors if you possibly can. You do not have to be afraid of exposure, for cold will not hurt you if you keep your body in proper condition. I have slept out in a rubber blanket, with the rain beating on my head and face; I have spread a rubber blanket on a hummock in the midst of a swamp, and waked up in the morning with my hair and face soaked in cold, white fog, but I never caught cold from such things; there is no harm whatever in dampness or in "night air," if you are in proper condition. Of course, you may get your ears frostbitten in the middle of winter, but you can have a sleeping hood to remove that danger.