Balneotherapeutics (Lat. balneum, a bath, and Gr. θεραπεύειν, to treat medically). The medical treatment of disease by internal and external use of mineral waters is quite distinct from "hydrotherapy," or the therapeutic uses of pure water. But the term "balneotherapeutics" has gradually come to be applied to everything relating to spa treatment, including the drinking of waters and the use of hot baths and natural vapour baths, as well as of the various kinds of mud and sand used for hot applications. The principal constituents found in mineral waters are sodium, magnesium, calcium and iron, in combination with the acids to form chlorides, sulphates, sulphides and carbonates. Other substances occasionally present in sufficient quantity to exert a therapeutic influence are arsenic, lithium, potassium, manganese, bromine, iodine, etc. The chief gases in solution are oxygen, nitrogen, carbonic acid and sulphuretted hydrogen. Argon and helium occur in some of the "simple thermal" and "thermal sulphur waters." There are few doctors who would deny the great value of special bathing and drinking cures in certain morbid conditions.

In the employment of the various mineral waters, many of the spas adopt special means by which they increase or modify their influence, e.g. the so-called "aromatic" or "medicated" baths, in which substances are mixed to exert a special influence on the skin and peripheral nerves. Of these the "pine-needle" bath has the greatest repute; it is made by adding a decoction of the needles or young shoots of firs and pines. Fir wood oil (a mixture of ethereal oils) or the tincture of an alcoholic extract acts equally well. The volatile ethereal constituents are supposed to penetrate the skin and to stimulate the cutaneous circulation and peripheral nerves, being eliminated later by the ordinary channels. Similar effects follow the addition to the bath of aromatic herbs, such as camomile, thyme, etc. For a full-sized bath 1½ to 2 lb of herbs are tied in a muslin bag and infused in a gallon of boiling water; the juices are then expressed and the infusion added to the bath. Astringent baths are prepared in a similar way from decoctions of oak bark, walnut leaves, etc. In many spas on the European continent baths are prepared from peat or mud mixed with hot mineral water.

Mineral peat consists of decomposing vegetable soil that has been so long in the neighbourhood of the medicinal spring that it has undergone peculiar and variable chemical changes. This is mixed with the hot mineral water until the bath has the desired consistency, the effect on the patient being in almost direct proportion to the density. These baths vary greatly in composition. Mud baths are chiefly prepared from muddy deposits found in the neighbourhood of the springs, as at St Amand. They act like a large poultice applied to the surface of the body, and in addition to the influence of the temperature, they exert a considerable mechanical effect. The pulse is accelerated some 6 to 12 beats a minute, the respiration number rises, and the patient is thrown into a profuse perspiration. They have very great value in gouty and rheumatic conditions and in some of the special troubles of women.

There are certain conditions in which mineral water treatment is distinctly contra-indicated. Advanced cardiac disease and cardiac cases with failure of compensation must pre-eminently be treated at home, not at a spa. Advanced arterio-sclerosis, any form of serious organic visceral disease, advanced cirrhosis, pulmonary tuberculosis with a tendency to haemoptysis, much elevation of temperature or emaciation, are all entirely unsuited for this form of treatment. Serious organic nervous diseases, great nervous depression and old cases of paralysis are all contra-indicated. Any trouble, however suited in itself for spa treatment, must be considered inapplicable if complicated with pregnancy.

In advising balneotherapeutic treatment in any case, all the conditions and habits of the patient - pecuniary, physical and psychical - must be considered, as the spa must be fitted to the patient, not the patient to the spa. Besides the particular disease, the idiosyncrasy of the patient must be considered, the same morbid condition in different people requiring very different treatment. Retarded convalescence is a condition often treated at the spas, although hygienic surroundings, both mental and physical, are usually all that is necessary to ensure complete recovery. After rheumatic fever, however, if the joints remain painful and the heart is dilated, the thermal gaseous saline water of Nauheim, augmented by Schott's resistance movements, will often appear to work wonders. Chronic rheumatism, where there is much exudation round a joint or incipient stiffness of a joint, may be relieved by hot thermal treatment, especially when combined with various forms of massage and exercises. Simple thermal waters, hot sulphur springs and hot muriated waters are all successful in different cases. Chronic muscular rheumatism can also be benefited in a similar manner. Diseases of the nervous system are on the whole treated by these means with small success.

Mental diseases other than very mild cases of depression should be considered inapplicable. Neurasthenics are sometimes treated at chalybeate or thermal muriated saline spas; but such treatment is entirely secondary to the general management of the case. Neuralgic affections and the later stages of neuritis, especially when dependent on gout or rheumatism, are often relieved or cured. Abdominal venosity (abdominal plethora), a feature of obesity, glycosuria, etc., are extremely well fitted for this form of treatment. The alkaline sulphated waters, the bitter waters and the common salt waters can all be prescribed, and after a short course can be supplemented with various forms of active and passive exercises. Diseases of the respiratory organs are far more suited for climatic treatment than for treatment by baths. Anaemia can usually be better or equally well treated at home, or by seaside residence or a sea voyage, though many physicians prescribe chloride of sodium waters, followed by a course of iron waters at some suitably situated spa. In the anaemia dependent on malarial infection, the muriated or alkaline sulphated waters at spas of considerable elevation and combined with iron and arsenic are often very beneficial.

Gravel and stone, if of the uric acid variety, can be treated with the alkaline waters, but the case must be under constant observation lest the urine become too alkaline and a deposition of phosphates take place on the already formed uric acid stone. Gout is so variable both in cause and effect that much discrimination is required in its treatment. Where the patient is of "full habit," with portal stagnation, the sulphated alkaline or mild bitter waters are indicated, especially those of Carlsbad and Marienbad; but the use of these strong waters must be followed by a long rest under strict hygienic conditions. Where this is impossible, a milder course must be advised, as at Homburg, Kissingen, Harrogate, Wiesbaden, Baden-Baden, etc. For very delicate patients, and where time is limited, the simple thermal waters are preferable.

For radiant heat and light baths and electric baths of all kinds, see Electrotherapeutics; and for compressed air baths, Aerotherapeutics. (See also Baths, Therapeutics, and the articles on diseases.)