The healthful effects of swimming in cold water in the open air result from the peculiar exercise, the temperature of the surrounding mediums, and the exhilaration of the spirits it causes. Before entering the water, and each time of leaving it, we enjoy an air-bath, the beneficial effects of which are not solely or chiefly dependent on the temperature, but are mainly owing to the actual impact of the atmospherical gases, and of the light, and possibly the direct rays of the sun upon the skin. In the water, if it be considerably colder than the ordinary summer air, say 50° to 60°, there is a rapid abstraction of heat from the surface, causing contraction of the cutaneous blood-vessels, and expulsion of their blood, which sometimes produces an almost painful sensation. If we then get out of the water at once, there is a rapid reaction and an intense glow, often so intense as to cause tingling over the whole surface, accompanied with visible redness, owing to the sudden reflux of the blood into the cutaneous vessels. If, however, we remain in the water in spite of the painful sensation caused by the first action of the cold, this gradually subsides, and if the water be not very cold, and our reactive powers good, and we keep ourselves always moving, the blood gradually returns towards the cutaneous surface, and we thus become accustomed to the low temperature, and can remain a considerable time in the water that seemed at first too chilly to be borne. When we then come out of the water we do not perceive any sudden reaction, but unless we have remained too long in the water, we only feel refreshed and invigorated.