In order to keep warm in winter it is, however, necessary that the cotton material should be of a certain thickness, besides being of the best quality and of the best make. As already mentioned it is of the utmost importance that the underwear should not fit too closely around the body, but that there should always be a layer of warm air between the skin and the garment. Instead of the present custom of wearing close-fitting trousers it would be much more beneficial to adopt the very large loose linen trousers that are worn in certain countries, such as Hungary. When once accustomed to such, and especially in the case of the younger generation, they can readily be worn also in winter time. Then, possibly, porous cotton can take the place of linen, although many people may feel just as warm in porous linen underwear; or we could possibly follow the example of an English gentleman who told me he never wore any underdrawers at all. In many European countries women, especially of the lower classes, wear no undergarments on their legs at all. In healthy women such a custom may be of great advantage, as it permits of the free passage of air and the elimination of the perspiration from the skin, being in effect a continuous free-air bath for the lower parts of the body. It is not so necessary to keep the lower extremities, except the feet, warm (provided that the feet are made warm by the constant motion of their muscles), as we do not need to be so well protected there as on the upper parts of the body; we also feel the cold less in these parts, which we can all appreciate if we are in the habit of walking much and not sitting about all day. Before putting on clean underwear we must be careful to ascertain that it has been thoroughly aired and is quite dry, for it happens in more cases than one knows of that the linen arrives from the laundry quite damp, although apparently it appears and feels dry. After having caught cold each time I changed my linen, after having perspired, I had the idea to put my vest over an electric lamp, and was surprised to see a cloud of moisture arise from it. As moisture readily absorbs the warmth of the body, we can therefore easily lose too much warmth and thus catch cold. Before putting on clean linen it is also advisable to rub the body with a brush (or rough towel) until the skin glows, and the linen itself should of course be put into a hot-air cupboard or be aired before a stove or fire, by which means many colds will be prevented; and these precautions are particularly necessary in all cases after free perspiration, in which latter case also a bath is very desirable before putting on our clean linen. It is of primary importance to change underwear every day, so as not to leave the products of perspiration on the skin for several days (see chapters on the hygiene of the skin and kidneys through perspiration).