Prevention is aimed at generally by maintaining health and a vigorous circulation. Anything which depresses the health and lowers vitality predisposes to frost-bite. In polar work the most important are exhaustion, hunger and vitamin deficiency. During a sledge journey vitamin deficiency, the consequent lack of resistance, and the more easily induced frost-bite create a condition of the gravest danger to the man or the party so affected. Locally, prevention lies in providing suitable clothing. In whatever form it takes the principle aimed at is the same, viz. _to provide a non-conducting air space round the skin_. The head and ears are protected by woollen and windproof helmets. The face cannot be covered, for masks get so heavily iced up as to make things worse. A cowl can be fitted to the helmet which, when thrown forward, to some extent shields the face from winds. The hands are enclosed in mitts, not gloves, in which the fingers are all together. The finger portion should be large enough to allow inclusion of the thumb when the hand is not in use. Sometimes two or three pairs are worn, the outer pair being of windproof material. To provide adequate foot protection which shall not at the same time be cumbersome is not an easy matter, for things which are loose about the feet are unwieldy. Woollen socks which enmesh the air in their stitches provide a good insulating air space. In low temperatures two, three or four pairs may be necessary. To prevent constriction of the feet it is of importance that each outer pair of socks should be a size larger than the one inside, and so they should be supplied in series. The cramming of a foot with too many pairs of socks into a boot too small for them is bad, for the circulation of blood to the toes is restricted and the air space is lost. Cold feet have often been cured by telling the wearer to _remove_ a pair of socks. All possible steps must be taken to see that the air space is not replaced by moisture, i.e. the feet and coverings must be kept dry. This is a difficult problem; coverings which allow of ventilation allow access of damp from the outside, and waterproof coverings retain perspiration. It is usually impossible to ensure absolute dryness, and therefore socks should always be changed before turning in to sleep. This should be made an inviolable rule, yet it is one which is often broken. Damp socks should not be placed in a freezing atmosphere, for the moisture in them will freeze and render difficult the putting of them on in the morning. They should be kept in the sleeping-bag or placed under the jersey. By this means they dry rapidly. Sennegrass may be used for taking up perspiration; it has the property of rapidly giving up its moisture. Some people prefer to use pieces of flannel instead of socks; the pieces are wrapped about the feet, and have the advantage that when taken off they can be spread out and thus dry more rapidly.