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Rh the great plague in 1605, and having contracted a rich marriage settled in 1609 at Vilvorde, near Brussels, where he occupied himself with chemical experiments and medical practice until his death on the 30th of December 1644. Van Helmont presents curious contradictions. On the one hand he was a disciple of Paracelsus (though he scornfully repudiates his errors was well as those of most other contemporary authorities), a mystic with strong leanings to the supernatural, an alchemist who believed that with a small piece of the philosopher’s stone he had transmuted 2000 times as much mercury into gold; on the other hand he was touched with the new learning that was producing men like Harvey, Galileo and Bacon, a careful observer of nature, and an exact experimenter who in some cases realized that matter can neither be created nor destroyed. As a chemist he deserves to be regarded as the founder of pneumatic chemistry, even though it made no substantial progress for a century after his time, and he was the first to understand that there are gases distinct in kind from atmospheric air. The very word “gas” he claims as his own invention, and he perceived that his “gas sylvestre” (our carbon dioxide) given off by burning charcoal is the same as that produced by fermenting must and that which sometimes renders the air of caves irrespirable. For him air and water are the two primitive elements of things. Fire he explicitly denies to be an element, and earth is not one because it can be reduced to water. That plants, for instance, are composed of water he sought to show by the ingenious quantitative experiment of planting a willow weighing 5 ℔ in 200 ℔ of dry soil and allowing it to grow for five years; at the end of that time it had become a tree weighing 169 ℔, and since it had received nothing but water and the soil weighed practically the same as at the beginning, he argued that the increased weight of wood, bark and roots had been formed from water alone. It was an old idea that the processes of the living body are fermentative in character, but he applied it more elaborately than any of his predecessors. For him digestion, nutrition and even movement are due to ferments, which convert dead food into living flesh in six stages. But having got so far with the application of chemical principles to physiological problems, he introduces a complicated system of supernatural agencies like the archei of Paracelsus, which preside over and direct the affairs of the body. A central archeus controls a number of subsidiary archei which move through the ferments, and just as diseases are primarily caused by some affection (exorbitatio) of the archeus, so remedies act by bringing it back to the normal. At the same time chemical principles guided him in the choice of medicines—undue acidity of the digestive juices, for example, was to be corrected by alkalies and vice versa; he was thus a forerunner of the iatrochemical school, and did good service to the art of medicine by applying chemical methods to the preparation of drugs. Over and above the archeus he taught that there is the sensitive soul which is the husk or shell of the immortal mind. Before the Fall the archeus obeyed the immortal mind and was directly controlled by it, but at the Fall men received also the sensitive soul and with it lost immortality, for when it perishes the immortal mind can no longer remain in the body. In addition to the archeus, which he described as “aura vitalis seminum, vitae directrix,” Van Helmont had other governing agencies resembling the archeus and not always clearly distinguished from it. From these he invented the term blas, defined as the “vis motus tam alterivi quam localis.” Of blas there were several kinds, e.g. blas humanum and blas meteoron; the heavens he said “constare gas materiâ et blas efficiente.” He was a faithful Catholic, but incurred the suspicion of the Church by his tract De magnetica vulnerum curatione (1621), which was thought to derogate from some of the miracles. His works were collected and published at Amsterdam as Ortus medicinae, vel opera et opuscula omnia in 1668 by his son Franz Mercurius (b. 1618 at Vilvorde, d. 1699 at Berlin), in whose own writings, e.g. Cabbalah Denudata (1677) and Opuscula philosophica (1690), mystical theosophy and alchemy appear in still wilder confusion.

See M. Foster, Lectures on the History of Physiology (1901); also Chevreul in ''Journ. des savants'' (Feb. and March 1850), and Cap

in ''Journ. pharm. chim.'' (1852). Other authorities are Poultier d’Elmoth, Mémoire sur J. B. van Helmont (1817); Rixner and Sieber, Beiträge zur Geschichte der Physiologie (1819–1826), vol. ii.; Spiers, Helmont’s System der Medicin (1840); Melsens, Leçons sur van Helmont (1848); Rommelaere, Études sur J. B. van Helmont (1860).

 HELMSTEDT, or more rarely Helmstädt, a town of Germany, in the duchy of Brunswick, 30 m. N.W. of Magdeburg on the main line of railway to Brunswick. Pop. (1905) 15,415. The principal buildings are the Juleum, the former university, built in the Renaissance style towards the close of the 16th century, and containing a library of 40,000 volumes; the fine Stephanskirche dating from the 12th century; the Walpurgiskirche restored in 1893–1894; the Marienberger Kirche, a beautiful church in the Roman style, and the Roman Catholic church. The Augustinian nunnery of Marienberg founded in 1176 is now a Lutheran school. The town contains the ruins of the Benedictine abbey of St Ludger, which was secularized in 1803. The educational institutions include several schools. The principal manufactures are furniture, yarn, soap, tobacco, sugar, vitriol and earthenware. Near the town is Bad Helmstedt, which has an iron mineral spring, and the Lübbensteine, two blocks of granite on which sacrifices to Woden are said to have been offered. Near Bad Helmstedt a monument has been erected to those who fell in the Franco-German War; in the town there is one to those killed at Waterloo. Helmstedt originated, according to legend, in connexion with the monastery founded by Ludger or Liudger (d. 809), the first bishop of Münster. There appears, however, little doubt that this tradition is mythical and that Helmstedt was not founded until about 900. It obtained civic rights in 1099 and, although destroyed by the archbishop of Magdeburg in 1199, it was soon rebuilt. In 1457 it joined the Hanseatic League, and in 1490 it came into the possession of Brunswick. In 1576 Julius, duke of Brunswick, founded a university here, and throughout the 17th century this was one of the chief seats of Protestant learning. It was closed by Jerome, king of Westphalia, in 1809.

See Ludewig, Geschichte und Beschreibung der Stadt Helmstedt (Helmstedt, 1821).

 HELMUND, a river of Afghanistan, in length about 600 m. The Helmund, which is identical with the ancient Etymander, is the most important river in Afghanistan, next to the Kabul river, which it exceeds both in volume and length. It rises in the recesses of the Koh-i-Baba to the west of Kabul, its infant stream parting the Unai pass from the Irak, the two chief passes on the well-known road from Kabul to Bamian. For 50 m. from its source its course is ascertained, but beyond that point for the next 50 no European has followed it. About the parallel of 33° N. it enters the Zamindawar province which lies to the N.W. of Kandahar, and thenceforward it is a well-mapped river to its termination in the lake of Seistan. Till about 40 m. above Girishk the character of the Helmund is that of a mountain river, flowing through valleys which in summer are the resort of pastoral tribes. On leaving the hills it enters on a flat country, and extends over a gravelly bed. Here also it begins to be used in irrigation. At Girishk it is crossed by the principal route from Herat to Kandahar. Forty-five miles below Girishk the Helmund receives its greatest tributary, the Arghandab, from the high Ghilzai country beyond Kandahar, and becomes a very considerable river, with a width of 300 or 400 yds. and an occasional depth of 9 to 12 ft. Even in the dry season it is never without a plentiful supply of water. The course of the river is more or less south-west from its source till in Seistan it crosses meridian 62°, when it turns nearly north, and so flows for 70 or 80 m. till it falls into the Seistan hamuns, or swamps, by various mouths. In this latter part of its course it forms the boundary between Afghan and Persian Seistan, and owing to constant changes in its bed and the swampy nature of its borders it has been a fertile source of frontier squabbles. Persian Seistan was once highly cultivated by means of a great system of canal irrigation; but for centuries, since the country was devastated by Timur, it has been a barren, treeless waste of flat alluvial plain. In years of exceptional flood the Seistan lakes spread southwards into an overflow channel called the 