PARAGUAY                                               1420                                             PARCHMENT

Paraguay, river of South America, rises in the Brazilian state of Matto Grasso, and flows southwesterly into the Parana. Its largest tributaries are the Jauru, Cuyab, Tacuary, Mondego, Aoa, Pilcomayo and Vermejo. The river is 1,800 miles long, and is navigable to the mouth of the Cuyab. It was declared open in 1852, and now has steamers running upon it, carrying mail from Rio Janeiro to Cuyab. At its outlet the Parana (a. v.), with its tributaries, forms the large estuary of Rio de la Plata (q. v.).

Parallax (pr'al-lăks), an optical and astronomical term used to denote the change in direction of an object due to a change in the position of the observer. This phenomenon is, perhaps, most easily observed in viewing a landscape from a railway train. When one's attention is concentrated upon any point in the landscape, all the more distant points appear to move in the same direction as the train, while the nearer points appear to move in a direction opposite that of the train. Thus, as the observer continually changes his position, being on the moving train, the direction of the point to which his attention is directed is continually changing. In the same way, if one could suddenly step from Chicago to New York on any moonlight night, the position of the moon among the fixed stars would also suddenly change. Since the earth is rotating and carrying the observer with it, the position of the moon or of one of the planets among the fixed stars depends upon the hour of the day at which the observation is made as well as upon the latitude and longitude of the observer. Accordingly, astronomical observations of this kind are all "reduced" to the center of the earth ; that is, the position of a heavenly body is given as that which it would appear to have for an observer situated at the center of the earth. Parallax of this kind is called diurnal. There also is a parallax due to the motion of the earth in its orbit about the sun; this is known as annual parallax, because it goes through all its changes in the course of one year. The principle of parallax is one of great usefulness in adjusting certain optical instruments and in making certain optical measurements. See Young's General Astronomy.

Paramaribo (păr'-mr'-bō), the capital of Dutch Guiana, lies on the Surinam, about ten miles from its mouth. It has broad streets, wooden houses, a governor's palace, a court of justice, two forts and a park. Almost all the trade of Dutch Guiana (q. v.) is centered here. Population 54,085.

Parana (pā'r-nā'), a large South American river, rises as the Rio Grande about 100 miles northwest of Rio de Janeiro. Flowing northwest and west, it unites with the Paranahyba, and receives its name and flows southwest and south to the point where it is joined by the Paraguay. It then

flows through Argentina, uniting with the Uruguay to form Rio de la Plata. Its total length is nearly 2,000 miles, and it drains over 1,100,000 square miles of territory. Its longest tributaries are those named and the Mogy Guassu, Tiet Parana-panema, Ivahy, Iguassu and Salado. It is navigable for 705 miles, and has rapids over 100 miles in length immediately above the junction with the Iguassu. Parana also is a state of Brazil with an area of 85,430 square miles and population of 250,000.

Parasites (par'a-slts), among plants those which obtain food by attacking living plants or animals. The majority of parasitic plants are fungi (which see). Many of them have cultivated a very selective habit, restricting themselves to certain plants or animals or even to certain organs. Some of the highest plants are also parasitic, as, for example, the dodder, whose thread-like body is often seen enwrapping tall herbs like skeins of yellow yarn ; and the mistletoe, growing in tufts on the branches of trees. In every case the plant or animal attacked is called the host. Sometimes the attacks are harmless, but often they are very destructive. The results of the most destructive parasites have come to be spoken of as diseases, and among them are some of the common contagious diseases. Among animals representatives of almost any class or order may be parasitic. Many of the parasites are insects; some are parasites of other insects, some of vertebrates. Parasites may serve as hosts to lesser parasites. Some in their earlier stages live within their host, some or the host. The parasite frequently destroys its host. Numbers of insects injurious to vegetation are held in check by parasites that destroy eggs and larvae; the chalcis flies are parasitic upon grain weevils, the destructive scale insects have for enemies various internal parasites. A common and troublesome parasite is the bot-fly, pest of horses. Lice are thoroughly parasitic. So are many families of worms.

Parch'ment, the prepared skins of sheep, goats and calves, generally used to record wills, deeds and other important papers that demand durable material. The coarser kinds are used for drumheads and tambourines. After the hair is removed from the skin, it is stretched over a board and scraped on both sides, powdered chalk is spread on the flesh side, and then it is gone over with a pumice stone and rubbed until smooth. Unsized paper is sometimes dipped for a few moments in a solution of sulphuric acid, which renders it transparent, tough and impervious to water. This is called vegetable parchment, and is much used. Vellum is a fine parchment made from the skins of kids, lambs and young calves. Parchment has been used for writing upon since the earliest periods, and from the 10th to the 14th century was almost the only material that could be used for that purpose.