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.
The Tonic Effect of Cold Upon the System.—The effect of cold upon the muscles, when given in the form of a cold bath, douche, or spray, is to augment muscular energy and tone to a very great extent; this increased muscular tonicity is the cause of the slight shivering. The cold douche, if short,—one or two seconds,—and given with a pressure of from 25 to 30 pounds, is a powerful restorative in fatigue resulting from severe muscular effort, but it must be immediately preceded by a short hot bath, and must be followed by vigorous rubbing and wrapping in a hot blanket.
Short cold applications cause elevation of temperature and increased metabolism, while prolonged cold applications cause a fall of temperature and decrease of metabolism.
The tonic effect of cold water is believed to be due to the stimulation of the sympathetic nerve-centers. The sympathetic nervous system controls the blood-vessels, heart, the functions of secretion and excretion; and, indeed, all the vital functions of the body.
The sensation of well-being which accompanies the reaction following a general cold application is largely due to an increased activity of the cerebral circulation. Cold water is a physiologic tonic, and the cold bath, properly employed, increases the vital resistance to pathologic processes.
All applications of water at a temperature low enough to provoke vital resistance are tonic; hence, tonic effects are produced by all temperatures below 90° F., but the most certain and pronounced results are obtained from the douche in every form, which adds mechanical impact to the thermic effects of cold. The most durable tonic effects are produced by the frequent use of very cold and very short baths.
A tepid bath causes a lowering of the body temperature.