A hot-water bottle or fomentations, placed over the stomach for an hour or two after eating, increase the gastric secretions, and, when placed over the liver, increase the flow of bile. =The Physiologic Effects of Cold.=—In suitable cases a short general application of cold is a powerful heart tonic. Cold causes a contraction of the vessels of the skin and of those of the brain, with a dilatation of the internal vessels. There are pallor and coldness of the skin, and an almost instantaneous suspension of perspiration, which is dangerous only when the body is in a state of fatigue. If the application of cold is long continued, the surface becomes blue, the temperature of the muscles beneath the skin is lowered, thus checking heat-production in these muscles; the circulation is slowed, and the heart’s action is diminished in frequency. There is a goose-flesh appearance of the skin; a sensation of chilliness, trembling, shivering, chattering of the teeth; at first a quickening and then slowing of the pulse, and deep gasping respiration. When the cold application is considerably prolonged, the tendency to reaction is suppressed. There is an exhaustion of the nerve-centers as well as of the heat-producing powers of the body. Thus, the system gradually loses its power to resist the depressing effects of cold. The repeated chillings of the body increase the length of time required to return to the normal temperature. Applications of water below the temperature of the body always lower the temperature. _Reaction._—If the application of cold is of very short duration, of very low temperature, and given under high pressure, the phenomena of reaction begin immediately on its cessation. The reaction consists in a dilatation of the surface capillaries, with contraction of the internal vessels; redness of the skin; the skin is smooth, soft, and supple; there is a sensation of warmth, comfort, and well-being; respiration is slower and deeper; there are a fall of the internal temperature and increase of perspiration. Certain measures to favor reaction should be taken before the bath, such as exposure to the air of a warm room, drinking hot water, and short exercise of a rather vigorous kind. During the bath the measures which favor reaction are short, sudden applications of cold, friction while in the bath with the hand, and pressure effects in the douche. After the bath reaction is favored by vigorous rubbing, a thorough drying of the body, warm clothing, warm air of the room, and as vigorous exercise as the strength of the individual will permit.