This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
One object of bathing is to cleanse the skin; but it is also useful to strengthen and invigorate the whole frame. For strong healthy persons a cold bath is the best; in severe weather the temperature of the water should be raised to 15° C. (about 60° F.), at which it still feels quite cool to the surface. The first effect of a cold bath is to contract all the skin-vessels and make the surface pallid. This is soon followed by a reaction, in which the skin becomes red and full of blood, and a glow of warmth is felt in it. The proper time to come out of the bath is while this reaction lasts, and after emersion it should be promoted by a good rub. If the stay in the cold water be too prolonged, the state of reaction passes off, the skin again becomes pallid, and the person probably feels cold, uncomfortable, and depressed all day: such bathing is injurious instead of beneficial ; it lowers instead of stimulating the activities of the body. How long one may remain in cold water with benefit, depends greatly on the individual; a vigorous man can bear and set up a healthy reaction after much longer immersion than a feeble one; moreover, a person used to cold bathing can with benefit remain in the water longer than one not accustomed to it. Of course, apart from this, the temperature of the water has a great importance. Water which feels cold to the skin may, as shown by the thermometer, vary within very wide limits of temperature. The colder it is, the shorter the time which it is wise to remain in it.
How often should soap be used in the bath ? Why is the too frequent use of soap not desirable? What is a good substitute for it in cases where soap is injurious to the skin ? How does an unclean skin influence internal organs ? When are its results apt to show themselves ?
The sweat glands secrete more vigorously when the body is heated, and the evaporation of their secretion cools it. In most fevers the sweat glands are paralyzed; and the abnormally warm body is not cooled by loss of the heat, which in health would have been carried off by the evaporating sweat.
It is perfectly safe to bathe when warm, provided the skin is not perspiring profusely; the common belief to the contrary notwithstanding. On the other hand, no one should enter a cold bath when feeling chilly, or in a depressed vital condition. It is not wise to take a cold bath immediately after a meal, for the afterglow of the skin tends to draw away too much blood from the digestive organs, which are then actively at work. The best time for a long bath is two or three hours after breakfast; but for a brief daily dip there is no better time than while the body is still warm from bed.
What ends are obtained by bathing? What sort of a bath should healthy persons take ? What is the primary effect of a cold bath on a healthy person ? What follows next ? When should one leave a cold bath? What happens if one stays too long in a cold bath? Point out conditions which influence the time of remaining with benefit in a cold bath.
Shower Baths abstract less heat from the body than an ordinary cold bath, and at the same time give it a greater stimulus, tending to set up the warm reaction. Hence they are valuable to persons in not very vigorous health.
Warm Baths, except occasionally for purposes of cleanliness, are medical remedies, and not proper things for daily use. While promoting the tendency to perspiration (which it is often important to do in disease), they also, if often repeated, lower the general vigor of the body. Persons in feeble health, who cannot stand an ordinary daily cold bath, may diminish the shock to the system by raising the temperature of the water they bathe in to any point at which it still feels cool to the skin.