Cerevisiae Fermentum. Yeast.
Preparation. — When an infusion of malt, (barley steeped in water, fermented, and dried in a kiln,) technically called Wort, is subjected to the process of fermentation, a dirty, grayish-brown substance, gradually separates, forming in part a frothy scum, and partly a sediment ; this is yeast, or barm.
History. — Yeast is a flocculent, frothy, somewhat viscid semifluid, of a sour, vinous odor, and a bitter taste ; it is a very mixed substance, containing water, alcohol, carbonic, acetic and malic acids, potassa, lime, and saccharo-mucilaginous extract. At 60° or in a damp atmosphere, it soon undergoes putrefaction, and exposed to a moderate heat, it becomes dry, hard, and brittle, and may then be preserved for a long time, though with the loss of much of its peculiar power. Yeast is insoluble in alcohol or water. Its most important property is, that when placed in contact with saccharine solutions at a temperature between 50° and 80°, it excites vinous fermentation in them, converting their su'^ar into carbonic acid and alcohol. This property it owes to its azotized globules or cells, which may be seen in it, when examined with a microscope, appearing as minute transparent vesicles, containing one or more granules. This property is much impaired by drying the yeast, and destroyed by a heat of 212°, the addition of strong alcohol, of several of the acids, or by continued trituration until all the vesicles have burst and lost their structure. It is also destroyed by boiling water, pyroligneous acid, salts of mercury, essential oils, etc.
Properties and Uses. — Stimulant, tonic, nutritious, antiseptic, and laxative. Used in typhoid fevers by mouth and injection, and in tympanitis by enema. In all malignant ulcerations of the throat and mouth, in diseases where there is a disposition to putridity, in scarlatina, and low stages of fever, with or without the addition of olive oil, which renders it more laxative, it will be found highly beneficial. Externally, in combination with elm bark and charcoal it forms an excellent emollient and antiseptic poultice in sloughing ulcers, stimulating the vessels, removing the tendency to gangrene, and correcting the fetor.
In the recent furunculoid epidemic which existed in this country and Europe, given internally, in conjunction with quinia, yeast was found effectual in the treatment of boils, carbuncles, and felons. The dose of yeast is from half an ounce to an ounce, every two or three hours.
Yeast has been advised in diabetes mellitus in doses of a fluidrachm three or four times a day, taken immediately before meals. It has in some instances proved efficacious, and is supposed to act by decomposing sugar or preventing its abnormal production in the stomach.
Off. Prep. — Cataplasma Fermenti.