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Investigator of the physiology of plants, physicist, and physician, b. at Breda in North Brabant, 8 Dec., 1730; d. at London, 7 Sept., 1799. He attended the Latin school at Breda, studied at Louvain, and later at Leyden, medicine, physics, and chemistry, and received the degree of Doctor of Medicine, although when and where the degree was obtained is unknown. Originally (from 1757) he practised medicine at Breda, but after the death of his father and on the invitation of the royal physician John Pringle he settled in London (1765), where he became acquainted with William Hunter, Alexander Monro, and George Armstrong. He studied the inoculation of children for small-pox, then a new theory, under Armstrong, and became a zealous advocate of it. In the spring of 1768 he was called to Vienna to inoculate the imperial family, a task which he accomplished successfully, notwithstanding the hostility of the Viennese physician Anton de Haen. In 1780 he travelled from Vienna to Paris in order to make the acquaintance of Benjamin Franklin. The great veneration he felt for Franklin caused Ingen-Housz to determine to settle in America, but unexpected occurrences, a long illness, and the death of Franklin in 1790 prevented the carrying out of this plan. He returned, therefore, to London to regain his health, and to await the restoration of political peace before returning to Vienna. The remainder of his life was spent at London. In 1775 he married Agatha Maria Jacquin, sister of the Viennese botanist Nicholas Jacquin; the marriage was childless.
To Ingen-Housz is due the discovery of the exchange of gas in plants under the influence of light. The green parts of plants, especially the leaves, exhale oxygen and absorb carbonic acid. In the dark the green parts exhale carbonic acid. The latter process goes on almost continuously in the parts of plants that are not green, as well as in the flowers and fruits. Before this Joseph Priestly (1733-1804) had explained the exhalation of oxygen as a result of the growth of plants, but later he adopted the views of Ingen-Housz, without mentioning the latter; the same course was followed by Jean Senebier (1742-1809). Ingen-Housz discovered the vegetable character of algae and introduced in microscopics the use of the cover glasses (mica-scales). Fired by Franklin's discoveries he devoted himself as early as 1757 to the study of electricity; the plate electrical machine is his invention. He supported the theory of Franklin's lightning conductor with a pointed tip, while in England a metal ball was used at the tip. Under his direction the palace and the powder-magazine at Vienna were equipped with Franklin's lightning-conductor. Mention should be made of his proposals concerning the construction of the ship's compass, the discovery that platinum is paramagnetic, the experiments begun with Franklin on the conduction of heat by metals, the discovery of oxy-hydrogen gas, and the invention of an air pistol with electrical ignition. Besides introducing inoculation for small-pox into Austria Ingen-Housz proposed the inhalation of oxygen in diseases of the lungs.
His most important works are, in botany: "Experiments upon Vegetables Discovering Their Great Power of Purifying the Common Air in the Sunshine" (London, 1779; German, 1780, 1786-1790; Dutch, 1780; French, 1780, 1785); "An Essay on the Food of Plants and the Renovation of Soils" (London, 1796; German, 1798; Dutch, 1797); in physics: treatises in "Philosophical Transactions": "Easy Methods of Measuring the Diminution of Bulk, taking place upon the mixture of common and nitrous air, together with experiments on platina" (1776); "Electrical Experiments to Explain how far the Phenomena of the Electrophorus may be accounted for by Dr. Franklin's Theory" (1778); "On Some New Methods of Suspending Magnetic Needles" (1779); "Account of a New Kind of Inflammable Air or Gas". "Vermischte Schriften physisch-medizinischen Inhaltes", translated by Niklas Karl Molitor (Vienna, 1782; 2nd ed., 2 vols., 1784), contains all the papers which appeared in the "Philosophical Transactions". The same miscellany appeared in Franch and Dutch in 1785; "Miscellanea physico-medica", ed. Jo. Andreas Scherer (Vienna, 1795). Manuscript collections of letters are privately owned, excepting the letters to Franklin which belong to the "American Philosophical Society" of Philadelphia; 27 letters written by Ingen-Housz are in the Imperial Library at Vienna; Franklin's letters, verbally in part, are to be found in the "Auktionskatalog VIII" of 11 Mar., 1901, issued by Gilhofer and Ranschburg of Vienna.
Old biographies by M.J. GODEFROI (1875) and TREUB (1880), in De Gids, No. 9, both in Dutch. The latest biography and an exhaustive one is by WIESNER, Jan Ingen-Housz, Sein Leben und sein Wirken als Naturforscher und Arzt (Vienna, 1905).