What are the various uses of this elaborate organ? In the first place, it serves as a protection to the softer parts beneath. Secondly, it serves to regulate the temperature of the body, by preventing, on the one hand, the too rapid radiation of the natural heat, and, on the other, by providing a very large surface for the evaporation of the constantly exuding perspiration, it prevents the overheating of the body. Thirdly, it is constantly removing from the body certain effete materials. These are the scales of the cuticle (which we remove whenever we wash and rub the surface), the perspiration, and the sebaceous, or greasy secretion. The amount of sweat varies immensely; it may be almost nil, or as much as a pint in an hour. The secretion of sweat is influenced by the temperature of the air, by exercise, by the drinking of fluids (especially warm fluids), and notably by the emotions. There can be no doubt that the secretion of a certain amount of sweat is necessary for perfect health; and it is the common experience of all that the checking of perspiration is very liable to be followed by dangerous internal congestion. It has been demonstrated on some of the lower animals that, if the skin be shaved and varnished, death speedily ensues. This has been spoken of as a sort of cutaneous suffocation, death taking place owing to the charging of the blood with matter which should have been removed by the skin. It has been asserted, however, that death is due to cold in these cases; and it has certainly been demonstrated that animals so treated live much longer provided they be kept warm by a layer of cotton wool. Sometimes the skin is superficially destroyed by accidental burning or scalding, and it is well recognised that a burn or scald is dangerous to life in proportion to its superficial extent, rather than to its depth or severity. The blood-vessels of the skin vary much in size under different circumstances, and the different degrees of pallor or redness of the skin are due to the condition of these superficial blood-vessels. The phenomenon of blushing is well known; and this should serve to remind us that the emotions can not only influence the amount of perspiration, but the size of the cutaneous blood-vessels. The intimate relations existing between the skin and the great nerve-centres should never be lost sight of. The cutaneous blood-vessels enlarge in certain fevers, as scarlet-fever and measles; they can be made to enlarge also by the application of warmth, or irritants, such as mustard, or the stroke of a whip. Contraction of the blood-vessels is most marked in conditions of fear, or as the result of the prolonged application of cold.