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LEFT HYDROSULPHURIC ACID 99 HYMANS tal level. If two or more liquids be placed in the same vessel they will ar- range themselves according to their rela- tive densities, after which the equi- librium vnll be stable. According to Hallam, the real creators of the science were Castellio (1577-1644), and Torri- celli (1608-1647). HYDROSULPHURIC ACID, or sul- phuretted hydrogen or hydrothionic acid (H:;S), is a colorless inflammable gas produced by the putrefaction of sulphur- ous organic matters. Many mineral wa- ters contain it naturally. It may be ar- tificially produced by burning sulphur vapor in hydrogen, or by passing hydro- gen through sulphur. It has a sweet taste but a very nauseous odor as of rotten eggs. It has poisonous effects when breathed, and experiments have shown that birds perished in air which contained Usooth part of the gas. HYDROTHERAPY, the scientific use of water in the treatment of human dis- orders and ailments. This is one of the oldest knoMTi curative methods, for it is known that Hippocrates used it in the treatment of many kinds of disease, and it is also a matter of record that the Emperor Augustus had a personal hy- dropathic physician. There were many practitioners of hydrotherapy during the Middle Ages, and in 1723, Niccolo Lan- zani, a physician of Naples, issued a treatise on some phases of the subject, as did Dr. Bayard and Sir John Floyer in England at about the same time, and in 1797 Dr. Currie published "The Medi- cal Report of the Effects of Water" in which the use of cold water for fevers was advocated. About 1820, Vincent Priessnitz, not a doctor but a Silesian farmer, insisted that water was a cure for a great many ailments because of its beneficial effects upon him, and he be- gan to practice his ideas upon his neigh- bois with remarkable results. It was he who introduced many of the methods of using water, such as the sheet bath, the compress, and the douche. He insisted that his patients drink large quantities of water, take vigorous outdoor exercise, pay strict attention to their diet, and have long periods of complete relaxation, thus combining all the resources of hy- giene for his new system of treatment, which was so successful that in twenty years of treatment he had only about 40 deaths out of nearly seven thousand patients. In 1883 Dr. Winternitz, a Ger- man, established the scientific principle that water may be used internally for its own properties, and either internally or externally as a mechanical carrier of heat or cold, and may be used in any of its three physical forms — ice (solid), liquid, or steam (gas). While the most modern practice does not consider water a cure-all, there are few physicians who do not use hydrotherapy in some form, such as ablution, affusion, the drip sheet, wet pack, compress, tub bath or douche. HYDROTHORAX, a name given to serous fluid occupying the pleura. It may take place as the result of inflam- mation, also in heart disease, in disease of the kidneys, and sometimes in anaemia. HYERES (e-ar') a small town of France, 3 miles from the Mediterranean. It is celebrated for the beauty of the situation and the mildness of the climate, and is therefore much resorted to by for- eigners suffering from consumption or nervous complaints. HYGIENE, the study of the preven- tion of disease, the art of preserving health, through wise sanitary precau- tions, such as attention to diet, regimen, etc. HYGROMETER (hi-grom'eter), an instrument for measuring the compara- tive moisture of the air. There are three kinds: (1) those which act by absorp- tion; (2) by condensation, and (3) those in which the hygrometric condi- tion is deduced from observations of a wet and dry bulb. Of the first class is the hygrometer of Saussure (died 1799). It consists of a human hair boiled in lye, and acts by absorption and evaporation, lengthening or contracting as the air is more or less moist. HYL.S30SAURUS (hi-le-o-sou'ros), a gigantic fossil lizard discovered in the Wealden formation of Tilgate Forest. Its probable length was about 25 feet. It is one of the Ornithoscelida, the group which presents a structure intermediate between that of existing birds and rep- tiles. HYMANS, PAUL, a Belgian states- man. He was born in Brussels in 1865 and was educated at Brussels University. Since 1900 has been member of the House of Representatives for Brussels, and of the Brussels Municipal Council since 1911; professor for some years at Brussels University and vice-president of the University's Board. In 1915 he became Belgian envoy extraordinixry and minister plenipotentiary to the Court of St. James, and in 1917 Minister for Foreign Affaires in the Belgian Govern- ment. His works include: "Histoire parlementaire de la Belgique"; "Brus- sels Moderne"; "Frere Orban"; "Por- traits, Essais et Discours."