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Rh spoken of under the name of parangi. The name framboesia was first given to the disease by Sauvages in 1759 from the likeness of the typical excrescences to a raspberry. For many years yaws was thought to be peculiar to the African negro, either in his home (both west and east coasts) or in the West Indies and Brazil. But a disease the same in every respect has long been known in the East Indies (first mentioned by Bontius early in the 17th century), affecting the Malays rather than the negroes, its chief seats being Amboyna, Ternate, Timor, Celebes, Java and Sumatra. It has been identified by De Rochas and other observers in New Caledonia and Fiji.

Aetiology. — Yaws is a highly contagious disease. It is neither hereditary nor congenital. The disease spreads by contact with previously infected cases, though it has been stated that infection also arises from inhabiting dirty houses, the floors and walls of which are contaminated with yawey matter from former yaw cases; and it is also believed, and has been proved by experiment, that infection may be conveyed by flies, which act as go-betweens, carrying infective material from a yaws sore to an ordinary ulcer. The virus must be introduced directly through a breach of the skin or mucous membrane; an attack in childhood gives a large degree of immunity for the rest of life. A micro coccus was found by Pierez and Nicholls in- the tubercles of yaws, but a pure culture of this micro-organism failed to give rise to yaws in animals into whom it was injected experimentally, and in no instance was it present in the blood. In 1905 Aldo Castellani demonstrated in yaws the presence of a slender spirillum, which he named the Spirochaeta pertenuis or Spirochaeta pallidula. It was also experimentally proved by him (1) that the material taken from persons suffering from yaws and containing the Spirochaeta pertenuis is infective to monkeys; (2) that when the Spirochaeta pertenuis is removed by filtration the material becomes inert; (3) that the injection of blood from the general circulation of a yaws patient gave positive results in monkeys; (4) by means of the Bordet-Gengou reaction it is possible to detect specific yaws anti-bodies and antigen.

The prophylaxis consists in the segregation of the patients suffering from the disease, the antiseptic dressing of the eruption, the application of a covering to protect it from flies, and the thorough cleansing and disinfection of infected houses and clothing, even the demolition of houses in endemic centres, and finally the compulsory notification of cases of yaws to the local sanitary authority.

As regards treatment, the malady in a person of good constitution runs its course and gets well in a few weeks. Whatever tends to check the eruption, such as exposure to chill, is to be avoided. A week’s course of cream of tartar and sulphur (confection of sulphur) at the beginning of the illness is often resorted to, so as to bring the eruption well out. The patient should remain indoors, in a well-aired room, and take daily warm baths and diluent drinks. If the excrescences are flabby and unhealthy, it is an indication for generous diet. When the eruption is declared, iodide of potassium and arsenic are very beneficial. As external applications, weak lotions of zinc or carbolic acid may be used, and, if the excrescences are irritable, a watery solution of opium. Tedious and unhealthy yaws should be dressed with a wash of sulphate of zinc or of copper; the same may be applied to a yaw ulcer. The crab yaws of the horny soles or palms, after they are let through by paring the cuticle, may be dusted with alum powder.

YAZDEGERD (“made by God,” Izdegerdes), the name of three Sassanid kings of Persia. (1) ., son of Shapur III., 399–420, called “the sinner” by the Persians, was a highly intelligent ruler, who tried to emancipate himself from the dominion of the magnates and the Magian priests. He punished the nobles severely when they attempted oppression; he stopped the persecution of the Christians and granted them their own organization. With the Roman Empire he lived in peace and friendship, and is therefore as much praised by the Byzantine authors (Procop. Pers. i. 2; Agath. iv. 26) as he is blamed by the Persians. After a reign of twenty years he appears to have been murdered in Khorasan. (2) ., was the son of Bahram V. Gor, 438–457. He persecuted the Christians and Jews, and had a short war with Rome in 441. He tried to extend his kingdom in the East and fought against the Kushans and Kidarites (or Huns). (3) ., a grandson of Chosroes II., who had been murdered by his son Kavadh II. in 628, was raised to the throne in 632 after a series of internal conflicts. He was a mere child and never really ruled; in his first year the Arabic invasion began, and in 637 the battle of Kadisiya decided the fate of the empire. Ctesiphon was occupied by the Arabs, and the king fled into Media. Yazdegerd fled from one district to another, till at last he was murdered at Merv in 651 (see, sect. A. 1). The Parsees, who use the old Persian calendar, continue to count the years from his accession (era of Yazdegerd, beginning June 16th, .. 632).

YEAST (O.E. giest or gyst; the root yes-, to boil, ferment, is seen in Sansk. nir-yāsa, exudations from trees, and Gr. , to boil), a cellular organism produced in the alcoholic fermentation of saccharine liquids (see , , ).

YEATS, WILLIAM BUTLER (1865–), Irish author, son of J. B. Yeats (b. 1839), a distinguished Irish artist and member of the Royal Hibernian Academy, was born at Sandymount, Dublin, on the 13th of June 1865. At nine years old he went to live with his parents in London, and was sent to the Godolphin School, Hammersmith. At fifteen he went to the Erasmus Smith School in Dublin. Later he studied painting for a short time at the Royal Dublin Society, but soon turned to