8. CEREVISIAE (Saccharomyces).—FERMENTUM COMPRESSUM (Compressed Yeast), N.F.—An organized ferment. Yeast is the name applied to the frothy scum that forms on the surface of saccharine liquids and rises from the bungholes of newly brewed beer. Under the microscope this froth is shown to consist of particles which multiply with extraordinary rapidity when placed in a moderately warm temperature. The globular forms are considered as the spores of a fungus belonging to the genus Torula, the cells of which are but slightly united, sometimes forming branching chains, the mycelium being almost absent. Yeast is employed in hastening the fermentation of worts and in leavening dough in bread-making. Bottom or sediment yeast is found on the bottom of fermenting vessels. Two quite distinct methods of brewing are produced, depending upon the employment of one or the other of these varieties of yeast. For the purpose of the bakery, yeast is dried and formed into cakes. Beer yeast is official in the B.P. Yeast, under the title of fermentum, was official in the U.S.P., 1820-40, 1860-80, used as a tonic, laxative, etc., but at present rarely employed. As a local remedy, as poultice, in treatment of eruptions of boils, it still finds some favor.