This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
When water is withheld from the system for a considerable length of time its absence is first apparent in the secretions and excretions, and next in the various tissues of the body, the last of all being those of the nervous system. More than ten or twelve hours of abstention from drinking produces uncomfortable thirst, and one or two hours of violent exercise may do so at once.
Continued deprivation of water causes the blood, by virtue of its self-regulating power, to withhold fluid from the kidneys and digestive glands. The digestive secretions therefore become less fluid, of more intense reaction, and greatly diminished in quantity. The mucous surfaces become dry, and the dryness, owing to the passage of air and the consequent evaporation, is first felt in the mouth and pharynx. The diminution in the digestive secretions, as well as their altered strength, interferes with or retards their normal action upon the ingesta. The proper movement of the food in the stomach and intestines is retarded by its greater solidity and by the increased friction of the mucous walls, especially in the lower bowel. Constipation therefore results. The absorption of fluid through the walls of the alimentary canal is retarded, and nutrition suffers in consequence. Meanwhile the blood, to maintain its normal character, reabsorbs water from the lymph spaces and different tissues of the body. The muscles and other structures become dry and diminish in volume. Emaciation results, which quickly reaches an extraordinary and painful degree. The mind dwells on water constantly, and taste is diminished.
Finally, the nervous system suffers from dryness and various nervous symptoms ensue, so that, in addition to extreme muscular weakness and prostration, there may be convulsions, delirium, and finally coma and death.
As far as the individual is concerned, the suffering from deprivation of water is mainly confined to the sensations of thirst and dryness of the mouth. Thirst is commonly, and somewhat erroneously, referred to the mouth and the pharynx. It is true that the mucous membrane in these regions becomes dry when water is withheld, but thirst may be also keen when these surfaces are abundantly moist. The sensation is the result chiefly of the expression through the nervous system of the need of the body tissues in general for fluid, and it is referred to the mouth and throat from force of habit, which associates the act of swallowing fluid, and the use of certain muscles in that process, with the subsequent relief of thirst. In support of the above statement is a fact that I have several times witnessed in patients having a gastric fistula made in consequence of oesophageal stenosis, or in patients nourished wholly through nutrient enemata, that the sensation of thirst referred by them to the mouth is immediately relieved by the injection of water into the stomach through the fistula, or of salt and water into the rectum.
It is asserted that shipwrecked sailors in open boats have relieved their thirst by immersing their bodies in salt water. A very little water is possibly absorbed under these conditions through the skin. Ordinarily, however, the skin is not capable of absorbing fluid of any kind to a practical extent, but immersion in water prevents evaporation from the surface of the body, and by saving its loss in that direction lessens thirst. Sucking a slice of lemon or drinking water acidulated with a few drops of lemon juice or vinegar sometimes allays thirst better than plain water. The same may be said of barley and oatmeal waters. Lime juice and ice is another remedy. Bitartrate of potassium or very weak brandy may be used for the same purpose, and is sometimes more satisfying.
On one of the arctic expeditions which resulted disastrously the men had no water for two months, but ate snow, having no fuel to spare to melt it.
"Hot water, as hot as can be sipped, quenches thirst much better than cold" (Balfour).
Glycerin and water is sometimes used to allay thirst by rinsing the mouth. The glycerin, being viscid, coats the surface of the mucous membrane and prevents to some extent the drying by evaporation, but it is hygroscopic and tends to abstract water if used too strong, and practically it is of little service.
When it is undesirable to give water by the mouth, thirst may be relieved by injection of salt and water beneath the skin (see Hypo-dermoclysis) or into the rectum.
Thirst may be controlled somewhat when it is desirable to restrict the fluids ingested by giving small doses of opium (Riegel). It may be that part of the benefit derived from this drug in the treatment of diabetes is due to its controlling this sympiim. It is taken sometimes by professional fasters, who aim to abstain from all food, and from as much drink as possible. The latter is done because without food water tends to promote tissue waste too rapidly, and loss of strength would be more rapid upon no food and an excess of water than upon no food with water in great moderation.
Water is drunk at various temperatures from that of melting ice to 110° or 1120 F. It is sometimes stated that the temperature of water influences digestion, but the extent to which it does so is much exaggerated. Very cold water swallowed quickly in large amount is said to contract the stomach wall and stimulate the heart action. Lehman says that water drunk at 600 causes a fall in the pulse rate and in rectal temperature, but these observations lack confirmation. This subject, as well as that of the local action of hot water, will be found more fully discussed under the heading Temperature and Digestion.
Ice is often useful in the sick-room, but it should not be given to young infants. Cracked ice sometimes soothes an inflamed throat, and occasionally it allays nausea. It relieves thirst only temporarily, and this symptom may be increased by its prolonged use. If too much is swallowed it becomes lukewarm in the stomach and may be vomited.