If we want to preserve our youth for a long time and attain an old age, we must take all available means to avoid such air contaminated by billions of microbes and vitiated by the exhalation of so many human beings and animals, who also absorb much of the oxygen. To this is added the smoke from the numerous manufactories, houses, and plants, and the dust and exhalations from many noxious substances of various kinds. As, however, fortunately, all this vitiated air is generally found in the lower strata, always endeavor to find a lodging in the more elevated portions of the city, and on the highest floor possible if staying in an apartment house or in a hotel. If possible our houses should be built on the outskirts of the city, and preferably near a park, or wood, or at least a meadow where there is a free circulation of pure air. In our rooms, and especially in the sleeping room, the window, or at any rate the transom, should always stand open, and if possible also during the night. But when obliged to sleep in a room with a closed window to avoid the noise of the street traffic, the first thing to do in the morning, directly one gets up, is to open the window and let in the fresh air, and do not close the window again until night-time. When we are well covered we need not be afraid of catching cold. As a rule only those take cold who keep in a warm room and live at enmity with fresh air. Fresh air, as a matter of fact, never does any harm to its friends; it is only dangerous to its enemies. As Captain Svaerdrup, a member of Nansen’s expedition to the North Pole, told us, he and his comrades never suffered from colds as long as they were in the polar regions. They first caught them when they approached Christiania. When standing at the window inhale the fresh air deeply several times and retain it as long as possible before exhaling it. Indeed we could preserve our health much more effectively if we imitated the Indian and slept in the open air. It is a fact that many Indians possess great immunity to all kinds of fatigue, enjoy very robust health, and reach a green old age. This is undoubtedly due to the fact that they pass the whole of their life in the open air. When tuberculous people are kept under the free-air treatment we are, after all, only following the example of the red man. Nobody who is accustomed to live in a close room with heavy curtains at an average temperature of 75° to 80° from October to May, can imagine the pleasures of a wooden hut or tent for day and night use. When Dr. Pottenger, of the Monrovia Sanatorium, near Los Angeles, California, showed me around his little wooden cottages in which his patients lived, I simply envied them. I cannot imagine a more healthy dwelling-place than a tent in summer and a wooden hut in winter, with a stove in it for the cold weather; and if we cannot raise the heat over 75°, so much the better.