Lond. Edin. Dub. Yeast.

Syn. Leveure (F.), Giischt (G.), Fermento di cervogia (I)., Espuma de cerbeza ( S.)

This substance is the scum or frothy matter which collects on the surface of beer while fermenting. It soon undergoes the putrefactive fermentation, but may be preserved by drying it to the consistence of a slightly cohesive paste; in which state it is sold in Paris. It has been chymically examined by Westrumb, who obtained from it a variety of ingredients1; but its essential constituent, or the fermenting principle, is supposed to be gluten, or something very analogous to that vegetable principle. Its medical properties may, perhaps, be attributed to its containing the bitter of the hop, some ready-formed alcohol, and carbonic acid.

Qualities.-Yeast has a vinous, sour odour; a bitter taste; reddens the vegetable blues; and is insoluble in water and alcohol. When it is filtered, a matter remains on the filter which possesses properties similar to those of vegetable gluten; and by this separation the yeast loses the property of exciting fermentation, but recovers it again when the gluter is added. The addition of yeast to any vegetable substance containing saccharine matter excites fermentation in it, and carbonic acid gas is evolved.

Medical properties and uses.-Yeast is tonic and antiseptic. Some years ago it was given with seeming advantage in typhoid fevers attended with symptoms of putridity: but the facts brought forward in support of its efficacy require further confirmation.2 As an external application, however, to foul and sphacelating ulcers, when united with farinaceous matters in the form of cataplasm or poultice, it is productive of the best effects. It corrects the foetor of the discharge, assists sloughing, and promotes the formation of a benign and healthy pus.

The dose of yeast is at able-spoonful or two (about f ss.), repeated every second or third hour : generally combined with porter, or wine, and sugar. It is also administered in the form of a clyster.

Officinal preparation.- Cataplasma Fermenti, L. D.

1 From 15.142 parts of yeast, heobtained the following substances; potassa 13, carbonic acid 15, acetic acid 10, malic acid 45, lime 69, alcohol 240, extractive 120, mucilage 240, saccharine matter 315, gluten 480, and water 13.595 parts; besides some traces of phosphoric acid and of silica. Crell's Annals, 1796, and Thomson's Chymistry, 4th edit. v. 406.

2 It was suggested as a remedy in these complaints by the Rev. Mr. Cart-wright.