interval of several weeks (incubation period). Cases of yaws by infection are not unknown in white persons of good position, both children and adults, in the West Indies and elsewhere.
The nature of the disease is obscure. It is alleged to be hereditary by some, and denied to be so by others; the fact seems to be that some constitutions are much more susceptible than others, and susceptible at some periods or states of health more than at others. As an epidemic, the disease in a locality has seasons of activity and quiet. One attack in childhood gives a large degree of immunity for the rest of life. Yaws used to break out in the slaves on board Guineamen. Both in Africa and among the slaves in the West Indies it was a custom to inoculate the yaws, so as to get the attack over (called “buying the yaws”) or to get put upon the sick list.
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. Mercurial treatment is no longer in vogue. 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. The most intractable cases occur in badly nourished and anæmic subjects, and these will often go on for months in hospital without mending. Of late in the West Indies the disease has become largely a morbus miseriæ, and to that extent less amenable to treatment.
The date of the first appearance of yaws in the West Indies and Brazil is matter of dispute; the general belief is that it came in with the African Negro. After the emancipation in 1838 there was a marked decline in the prevalence of the disease in Jamaica and other colonies. In Jamaica it began to be seen again from 1854 to 1864, the cases being more of adult age than formerly. The worst recent centre of yaws has been Dominica, which is occupied by Negro communities unprovided with medical attendance. In 1871 the Government opened and maintained two special hospitals for yaws (under a board of commissioners), one at Morne Bruce near Roseau, and the other at Prince Rupert's. In Barbados and Antigua cases of yaws are rarely seen, the population being more Creole than Negro. Trinidad has a good deal of the disease from time to time in the inland villages; bad cases are admitted to the leper asylum at Port of Spain. In Grenada, which has a special yaws hospital, and in St Vincent the immigration of Hindu coolies received a check owing to the ravages made by the disease among them. It prevails also in San Domingo, Guadeloupe, and others of the Antilles. At Berbice and Essequibo there were 23 fatal cases in one year (1870). The disease is common in all parts of Brazil. In western Africa cases are found along the whole coast from the Senegal to the Congo, and in the interior (Timbuktu and Bornu). On the East Coast it is found in Mozambique, Madagascar, and the Comoros Its localities in the East Indies and islands of the Pacific have been already mentioned.
For the literature dealing with the subject, see Hirsch, Geographical and Historical Pathology (Engl. trans.), vol. ii., London, 1885 (New Sydenham Soc.).
YAZD, or Yezd, a city of Persia, capital of the district of Yazd, province of Farsistán, in 31° 50′ N. lat. and 54° 25′ E. long. Yazd stands on a flat sandy plain, about 50 miles broad and encircled by an amphitheatre of picturesque hills, on the high road between Ispahán and Karmán, 190 miles south-east of the former and 220 north-west of the latter place. The old and dilapidated walls enclose a very large space, which, however, is much encumbered with ruins, the population having fallen from about 100,000 at the beginning of the 19th century (Christie) to about 30,000 in 1868 (Smith), Since the famine of 1870 the place has recovered some of its former prosperity, and has at present (1888) an estimated population of 50,000, including 1000 Jews and about 4000 fire-worshippers, Yazd being the only town in Persia where these still form a separate community. There are fifty mosques, sixty-five public baths, eight public schools, but no building of any note except the chief mosque, a very old and decayed structure, which still presents a lofty and imposing frontage. With the exception of a fine new bazaar, which is well stocked with goods and much frequented the markets and other parts of the town are irregularly planned, with narrow dark streets and little life. Yazd is in fact a city of the wilderness, whose oasis, planted chiefly with mulberries and other fruit trees, is everywhere surrounded by the shifting sands, which at some points already threaten to encroach on the town itself (Macgregor). In this way was engulfed its predecessor, Old Yazd or Askizár, whose ruins are still visible 10 miles to the north-west on the road to Kashan. Nevertheless the local traders maintain their old reputation for intelligence and enterprise, and their agents still visit the distant markets of India, Java, and China. The trade with India formerly carried on through Shiraz now takes the more direct route through Karmán. The exports are chiefly sugar, silks, opium (4000 chests in a single year to China), cordage, cotton, felts, and copper; the imports wheat, rice, cotton goods, and henna. This henna, together with rang for dyeing the hair, is brought from the Mináb and Bandar-Abbás districts to be ground and prepared for the Persian market. From the neighbouring villages and the remote province of Ghilán comes the raw material for the silk-looms, which produce two kinds—kasb and aluhí—both of the very finest quality. Other noted products of the local industries are the felts, equal to the best in Karmán, and the candied sugars and sweetmeats, in the preparation of which the fire-worshippers excel. A great drawback to Yazd is the defective and irregular supply of water, which largely depends on the yearly snow and rain fall on the surrounding hills. The annual revenue averages £35,000 to £40,000, of which three-fifths go to the public treasury; the rest supports the local administration and household of the governor, who resides in a kind of citadel within the city walls.
YEADON, a manufacturing town in the West Riding of Yorkshire, is situated on a hill north of Airedale, about 1 miles from Guiseley station on the Midland Railway and 8 miles north-west of Leeds. The streets are generally irregular and tortuous, but within recent years greater care has been taken in the arrangement of new buildings. The church of St John in the Pointed Gothic style, erected in 1843, consists of chancel and nave, with square tower surmounted by pinnacles. The town-hall and mechanics institute, a handsome Gothic building erected in 1883, includes a large public hall, the rooms of the Liberal club and of the local board, and class and lecture rooms. Yeadon is chiefly of modern growth, although wool-combing and cloth manufacture were carried on to some extent before the establishment of the first woollen-mill in 1831. Since 1850 the town has made rapid progress, and now possesses several mills, in which woollen cloths are manufactured, especially materials for ladies jackets, ulsters, mantles, &c. The township was formed out of Guiseley in 1845. The local board of health was established in 1863. The population of the urban sanitary district (area 1723 acres) was 5246 in 1871 and 6534 in 1881.
component of all sacchariferous juices when in the state of vinous fermentation. This subject is pretty fully dealt with under Fermentation (see vol. ix. pp. 92, 95, 97); one important application of yeast, however, viz., that which it finds in the baker's trade, is there only referred to. To produce a spongy loaf, the dough, before being made into loaves, is mixed with a ferment which, if allowed to act for a sufficient time before baking, produces alcohol and carbonic acid from a small portion of the actual or potential sugar present; and the carbonic acid, being liberated from within the dough, causes it to “rise.” In former times leaven (see Baking, vol. iii. p. 253) used to be employed exclusively. For higher classes of bakery
yeast is now preferred. The yeast produced so abundantly