the last to be brought under the rule of Moscow. It already existed in the time of Rurik (oth century); and Nestor mentions under the year 914 that Olga, wife of Igor, prince of Novgorod, was brought from Pleskov (i.e. Pskov). The Velikaya valley and river were from a remote antiquity a channel for the trade of the south of Europe with the Baltic coast. Pskov being an important strategic point, its possession was obstinately disputed between the Russians and the Germans and Lithuanians throughout the 11th and 12th centuries. At that time the place had its own independent institutions; but it became in the 12th century a prigorod of the Novgorod republic-that is a city having its own free institutions, but included in certain respects within the jurisdiction of the metropolis, and compelled in time of war to march against the common enemy. Pskov had, however, its own prince (defensor municipii); and in the second half of the 13th century Prince (Timotheus) Dovmont fortified it so strongly that the town asserted its independence of Novgorod, with which, in 1348, it concluded a treaty wherein the two republics were recognized as equals. Its rule extended over the territory which now forms the districts of Pskov, Ostrov, Opochka, and Gdov (farther north on the east side of Lake Peipus). The vyeche or council of Pskov was sovereign, the councils of the subordinate towns being supreme in their own municipal affairs. The council was supreme in all affairs of general interest, as well as a supreme court of justice, and the princes were elected by it; these last had to defend the city and levied the taxes, which were assessed by twelve citizens. But while Novgorod constantly showed a tendency to become an oligarchy of the wealthier merchants, Pskov figured as a republic in which the influence of the poorer classes prevailed. Its trading associations, supported by those of the working classes, checked the influence of the wealthier merchants.
This struggle continued throughout the 14th and 15th centuries. Nothwithstanding these conflicts Pskov was a very wealthy city. Its strong walls, its forty large and wealthy churches, built during this period, its numerous monasteries, and its extensive trade, bear testimony to the wealth of the inhabitants, who then numbered about 60,000. As early as the 13th century Pskov was an important station for the trade between Novgorod and Riga. A century later it became a member of the Hanseatic League. Its merchants and trading associations had factories at Narva, Reval and Riga, and exported fiax, corn, tallow, skins, tar, pitch, honey, and timber for ship-building. Silks, woollen stuffs, and all kinds of manufactured wares were brought back in exchange. In 12399 the prince of Moscow claimed the privilege of confirming the elected prince of Pskov in his rights; and though, fifty years later, Pskov and Novgorod concluded defensive treaties against Moscow, the poorer classes continued to seek at Moscow a protection against the richer citizens. After the fall of Novgorod (147 5) Pskov was taken (1510) by Basil Ivanovich, prince of Moscow, and a voyvode or deputy was nominated to govern the city. Moscow, at the end of the 17th century, abolished the last vestiges of self-government at Pskov, which thenceforward fell into rapid decay. Near this city the Teutonic knights inflicted a severe defeat upon the Russians in 1502. Pskov became a stronghold of Russia against Poland, and was besieged (1581) for seven months by Stephen Bathory during the Livonian War, and in 1615 by Gustavus Adolphus of Sweden. Under Peter the Great it became a fortified camp. (P. A. K.; J. T. BE.)
PSORIASIS, a skin affection characterized by the occurrence of flat dry patches of varying size covered with silvery white scales. Next to eczema and ringworm it is one of the most commonly found skin diseases. It occurs frequently during infancy and early adult life, and rarely begins after the age of fifty. Though a parasitic origin has been suggested, no bacteriological factor has yet been found, and it has been demonstrated that psoriasis may follow on nervous shock, gout, mental emotion and insufficient nourishment. It may also follow an attack of scarlet fever or erysipelas. The site of the disease may be determined by an abrasion or other injury of the skin, or even an irritation caused by friction of the clothing. The favourite starting point of the lesion is either the elbows or the fronts of the knees. It is nearly always symmetrical in its distribution, and spreads over the trunk and the extensor surfaces of the limbs, in contrast to eczema, which selects the flexor surfaces. The hairy scalp may also be affected. The eruption generally first shows itself as one or more papules, at first red and spreading, and later white from the formation of scales and red at the spreading margin, where it is surrounded by a hyperaemic zone. On removing the scales is seen a smooth hyperaemic zone dotted with red spots. The patches spread centrifugally and may remain stationary for a long time or coalesce with other patches and cover large areas of skin. In some cases involution of the central portion accompanies the spreading of the patch, and large concentric rings are formed. The lesions may persist for years, or spontaneously disappear, leaving behind a slight brown stain. The symptoms are usually slight and there is little or no irritation or itching, and no pain except in a form which is associated with osteo-arthritis. The disease, though of noted chronicity, is subject to sudden exacerbations, and may reappear at intervals after it has completely disappeared. It has little or no effect upon the general health. Several forms have been described, viz. the simple uncomplicated, the nervous, the osteo-arthritic, and the seborrhoeic. Varieties have also been named according to the character of the patches, such as psoriasis punctata, guttata, circinata or nummularis, or when large areas are involved and the skin is harsh, dry and cracked, it is known as psoriasis inveterate. The pathological changes taking place in the skin have been described as an inflammation of the papillae and corium, with a down-growth of the stratum mucosum between the papillae and an increase of the horny layer (keratosis). This latter, however, has been said to be due to the formation in it of tiny dry abscesses. The silvery appearance of the scales is due to the inclusion of air globules within them. The treatment is hygienic, constitutional and local. The clothing must be regulated so as to prevent undue perspiration or irritation or chafing of the skin. The most effective local application is chrysarobin used as an ointment. A bath of hot water and soap should first be given, or an alkaline bath, in order to remove all the scales; the ointment is then applied, but must be used over a small area at a time, as it is apt to set up dermatitis. Tarry applications, such as unguentum picis liquidae, creosote ointment or liquor carbonis detergens, are also useful and radio-therapy has caused a rapid removal of the lesions, but neither it nor the ointment has prevented subsequent recurrence. In chronic cases the sulphur-water baths of Harrogate, Aix-les-Bains and Aachen have been successful. The internal administration of small doses of vinum antimoniale, in acute cases, or of arsenic (in gradually increasing doses of the liquor arsenicalis) in chronic cases, is undoubtedly beneficial.
PSOROSPERMIASIS, the medical term for a disease caused by the animal parasites known as psorosperms or gregarinidae, found in the liver, kidneys and ureters.
PSYCHE (ψυχή), in Greek mythology, the personification of the human soul. The story of the love of Eros (Cupid) for Psyche is a philosophical allegory, founded upon the Platonic conception of the soul. In this connexion Psyche was represented in Greek and Graeco-Roman art as a tender maiden, with bird's or butterfly's wings, or simply as a butterfly. Sometimes she is pursued and tormented by Eros, sometimes she revenges herself upon him, sometimes she embraces him in fondest affection. The tale of Cupid and Psyche, in the Metamorphoses of Apuleius, has nothing in common with this conception but the name. In it Psyche, the youngest daughter of a king, arouses the jealousy of Venus, who orders Cupid to inspire her with love for the most despicable of men. Cupid, however, falls in love with her himself, and carries her off to a secluded spot, where he visits her by night, unseen and unrecognized by her. Persuaded by her sisters that her companion is a hideous monster, and forgetful of his warning, she lights a lamp to look upon him while he is asleep; in her ecstasy at his beauty