This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
Refrigerants are remedies which allay thirst, and give a feeling of coolness.
There appear to be two kinds of thirst: one of which is general, the other of which is local. Local thirst is occasioned by dryness of the mouth and fauces. It may be quenched by washing the mouth and gargling the throat with water, although none of it be swallowed, or by anything which will increase the flow of saliva, and thus keep the mouth and fauces moist. Thus, a pebble under the tongue, or chewed, will lessen thirst by increasing the secretion of saliva; and acids, both mineral and vegetable, as well as effervescing drinks containing carbonic acid and the juices of fruits, which contain either free vegetable acid or acid salts, acetates and tartrates, have a similar effect. When the secretion from the mouth and throat is very scanty, it is dried up by the passage of air to and fro in the process of respiration. The evaporation thus occasioned may be lessened, and the feeling of thirst diminished by the use of mucilaginous substances, which will form a thin coating over the mucous membrane of the mouth and pharynx. Thus, the addition of oatmeal to water will increase its power to quench thirst, and a very little milk added to water has a similar effect.
General thirst depends upon the condition of the organism generally, which appears to be due either to deficiency of water or excess of soluble and especially saline substances in the circulation.
General thirst is very often accompanied by local thirst, and may be partially alleviated by the means already described, but cannot be removed excepting by the introduction of water into the organism, or removal from it of the saline or other substances which are present in excess, or by lessening the excitability of that part of the nervous system by which the sensation of thirst is perceived.
This part of the nervous system, or thirst centre as Nothnagel calls it, is probably situated, according to him, in the occipital lobes of the brain, and it is possible that it may be irritated directly by mechanical injury, or by the condition of the blood circulating in it, as well as reflexly from mucous membranes, such as that of the mouth and throat, and possibly also from the kidneys. Its excitability is lessened by opium, and this may be used to diminish thirst in cases where other remedies fail to relieve.