YAM. 



YAM (Dioscorea saliva*). A climbing plant, 

 cultivated in the East and West Indies. Its 

 roots are very large, flattened, sometimes pal- 

 mated. It is boiled or roasted like the potato, 

 and is wholesome, palatable, and nutritious. 

 The flour is also used for puddings and bread. 

 The D. alata is equally cultivated; its root is 

 3 feet long, and often weighs 30 Ibs. Of both 

 kinds there are numerous varieties. 



YARD-DUNG. See FARM-YARD MANURE. 



YARD OF LAND. A quantity of land 

 which in some counties in England signifies 

 15 acres, in some 20, and in others 24, 30, and 

 34 acres. 



YARROW (Achilka}. A genus of showy, 

 free-flowering plants, succeeding well in any 

 common soil, and readily increased by divid- 

 ing the roots. The species are possessed of 

 aromatic, bitter, tonic, and stimulating quali- 

 ties. In England the following are indigenous 

 perennials : 



1. Sneezewort yarrow, or goose-tongue (A. 

 j>tar mil-it), which grows in wet hedges, or about 

 ihe banks of rivers, flowering in July and Au- 

 gust. The root creeps widely, and is difficult 

 of extirpation where the soil is moist. Stems 

 upright, about 2 feet high ; corymbose at the 

 top. Leaves sessile, linear, pointed, equally 

 and sharply serrated, and of a glaucous green. 

 Flowers numerous, small, milk-white in the 

 disk as well as in the radius, with an irregular 

 number of ligulate florets. The whole plant 

 has a pungent flavour, provoking a flow of 

 saliva, and this flavour renders it acceptable, 

 as Schreber asserts, to sheep, who delight es- 

 pecially in saltish food. The sneezing caused 

 by the dried and powdered leaves is rather 

 owin? to their little, sharp, marginal prickles. 

 Its name is derived from this property of caus- 

 ing sneezing. 



2. Serrated yarrow (A. serrata). This is a 

 much less common species, in which the root 

 is fibrous, leaves linear, lanceolate, downy, 

 deeply serrated. Flowers of a yellowish-white 

 or buff colour, not half the size of the forego- 

 ing. The whole herb has a powerful aromatic 

 scent and bitter flavour, somewhat like tansy. 



3. Common yarrow or milfoil (A. millifo- 

 linni), PI. 9, k. This species grows abundantly 

 in English meadows and pastures. The root 

 is creeping, with smooth, reddish, subterrane- 

 ous shoots, which are warm and agreeably 

 pungent, partaking of the flavour and salivat- 

 ing quality of the pellitory of Spain (A.py- 

 rethutn). Stems furrowed, erect, about a foot 

 high Leaves doubly pinnatifid, hairy; seg- 

 nr^nt.s linear, toothed, pointed. Flowers nume- 

 r< us ; white, occasionally reddish or purple. 

 The whole herb is astringent, and weakly aro- 

 matic. Although considered a bad weed in 

 pasture and arable lands, in consequence of 

 its creeping root, Dr. Anderson and others have 

 recommended it for cultivation ; but its pro- 

 ductive and nutrient properties are very inferior 

 to many other plants equally adapted to light 

 soils ; 64 drachms of the leaves and stems, cut 

 when in flower, afforded 98 grains of nutritive 

 matter. Linnagus says that its properties are 

 vulnerarv and styptic. An essential oil is ex- 



YEAST. 



traded from the flowers ; and aa ointrtuml 

 made of the leaves is reckoned good ag&mst 

 the scab in sheep. A. moschata, an exotic spe- 

 cies, a native of Italy, is sudorific and acrid, 

 and makes a wholesome food for cattle. 



4. Woolly yellow milfoil, or yarrow (A. to- 

 mcntosa). This species grows about dry hilly 

 pastures in Scotland and Ireland. The root is 

 woody, slightly creeping, with many long fibres. 

 Stems scarcely a foot high, curved at the base, 

 then erect. Leaves doubly pinnatifid, woolly, 

 segments linear, crowded, acute. Flowers 

 densely corymbose, on woolly stalks, of a 

 bright golden yellow. The whole herb, as well 

 as the flowers, has an aromatic scent when 

 rubbed. It serves to decorate rock-work in 

 gardens, but will not bear wet or shade. 



YEARLINGS. A term applied to calves, 

 colts, and other young stock, when they have 

 completed their first year. 



YEAST. The froth or scum which rises on 

 beer during the act of fermentation. (See 

 SHEWING and FERMENTATION.) It contains a 

 variety of components ; among others, carbon, 

 acetic and malic acids, alcohol, potassa, lime, 

 a saccharine, mucilaginous extract, gluten, and 

 water. 



Yeast is an article of the greatest importance 

 in domestic economy, forming a necessary in- 

 gredient in the manufacture of bread, which 

 would otherwise become heavy and unwhole- 

 some. When put in contact with saccharine 

 matters, at a temperature of between 50 and 

 60, it causes fermentation, and changes the 

 sugar into alcohol and carbonic acid. Yeast 

 may be dried and yet retain its properties, but 

 a temperature of 212 destroys it. 



The yeast prepared by the Hungarians will 

 keep for a whole twelvemonth. During the 

 summer season they boil a quantity of wheaten 

 bran and hops in water ; the decoction is not 

 long in fermenting, and when this has taken 

 place they throw in a sufficient portion of bran 

 to form the whole into a thick paste, which 

 they work into balls, that are afterwards dried 

 by a slow heat. When wanted for use they 

 are broken, and boiling water is poured upon 

 them ; having stood a proper time, the fluid is 

 decanted, and in a fit state for leavening bread. 

 See BREAD. 



"The substance called yeast or ferment, de- 

 rives its name from the power it possesses of 

 causing fermentation in sugar, or saccharine 

 vegetable juices. It possesses," says Liebig, 

 " all the characters of a compound of nitrogen in 

 the state of putrefaction and eremacausis. 



"Like wood in the state of eremacausis, yeast 

 converts the oxygen of the surrounding air into 

 carbonic acid, but it also evolves this gas from 

 its own mass, like bodies in the state of putre- 

 faction. (Colin.') When kept under water, it 

 emits carbonic acid, accompanied by gases of 

 an offensive smell (Thenard), and is at last con- 

 verted into a substance resembling old cheese. 

 (Proust.) But when its own putrefaction is com 

 pleted, it has no longer the power of inducing 

 fermentation in other bodies. The presence 

 of water is quite necessary for sustaining the 

 properties of ferment, for by simple pressure 

 its power to excite fermentation is much di 

 minished, and is completely destroyed by dry 



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