Conditions which are unfavorable to healthy reaction are: old age, infancy, exhaustion, either temporary or from an excessive loss of sleep, or extreme nervous exhaustion, obesity, rheumatic diathesis, unhealthy or inactive skin, profuse perspiration when accompanied by a state of fatigue, extreme nervous irritability, a very low temperature of the skin, an immediately preceding or impending chill, and extreme aversion to cold applications. The average temperature of the human nude skin is in the neighborhood of 90° F. The difference between the temperature of the skin and water is the chief element in determining the reaction of the individual. It is evident that water at a temperature of 90° F. would be neutral or indifferent; the difference of intensity of effect is in proportion to the difference of temperature of the water and skin. The duration of the cold procedure is an important element in the production of reaction. It may be laid down as a rule never to give any cold-water application without friction. The physical and psychic state of the individual exerts more or less influence upon his reactive capacity. An anemic, or otherwise depressed individual must be managed with great circumspection, because she bears heat abstraction badly. The hydriatic procedure must always be adapted to the reactive capacity of the bather. The woman must be thoroughly rubbed after the bath until a good reaction has occurred. Especial attention must be paid to the feet and legs. The bather should first be rubbed with a warm towel or sheet, and then with the bare hands of the attendant, as the warm hand greatly facilitates the reaction. The bather is by no means dry when the skin ceases to feel wet. So long as the skin is soft and spongy, it still contains moisture which has been absorbed by the superficial layers of the epidermis. The absorbed moisture, being left to evaporate after the bath, the individual is liable to become chilly and contract a cold, which is erroneously attributed to the bath itself. Other injurious effects following imperfect reaction after the cold bath are secondary chills or a continuous chill lasting for several hours. The hands and feet are cold, there is headache, not infrequently diarrhea, and other evidences of internal congestion, such as abdominal or ovarian pain, vertigo, etc. Reaction may be favored by covering the patient with blankets, surrounding her with hot-water bottles, and giving her hot tea to drink. Exercise should follow the bath. Walking for from twenty minutes to an hour is the most usual form of exercise. Very vigorous exercise for a short time cannot be substituted for moderate exercise for a longer time.