The feather beds, much used in Europe, are undesirable, as they are unsanitary and are too warm for nearly all seasons of the year. It is always best to sleep between clean linen sheets. For purposes of warmth, however, bear in mind that cotton is of very little value, whereas animal-product covers such as wool and down, or feathers, are exceptionally warm. Cotton comforters in cold weather are very heavy, but cold, whereas woolen blankets, wool-filled comforters or down- filled comforters are warm, but light. "A warmth without weight" should be the chief consideration in cold weather. And in using woolen coverings you can get sufficient warmth without much weight and with the very least quantity of covering. In summer use only a single woolen blanket or a light cotton coverlet over the sheet. When the nights are hot and sultry it would be well to use no covering of any kind. For warmth in winter special attention should be given to warm fabrics underneath the lower sheet as well as the coverings. One may become chilled from underneath if lying upon a thin mattress or an uncovered mattress. A wool-filled comforter, or double woolen blanket, placed over the mattress and under the sheet will contribute greatly to one's warmth. If the mattress is of proper thickness one can be comfortable with less covering and therefore less weight. However, I would suggest as a better plan the one that I have presented of sleeping in a virtual air bath the whole night through. The use of a pillow is necessary in nearly all cases. When one is sleeping on his back a pillow is certainly an objectionable feature. It tips the head forward and is conducive to round shoulders. A pillow is of value when sleeping on the side or in the partial face-downward position, as indicated in the illustration.