In Plate VII. (left side) there is represented a field of yeast, magnified 400 times. We see a mass of disjointed cells, such as appear after fermentations without sufficient aliment; of the kind represented some are nearly spherical, others oval or cylindrical, more or less elongated. If we mix a little of this yeast, of about the size of a pin’s head, with wort, and put the wort into a small, shallow, flat-bottomed basin, having a surface of about 1 square decimetre (10 sq. ins.) exposing it to the surrounding temperature, we shall find next day the bottom of the basin covered with a fine white deposit, of the forms of which we give a sketch in the right half of the plate. In this it will at once be observed that the cells sown have lost their interior granulations, having become more transparent and filled with a gelatinous protoplasm. The principal difference between the two halves of the plate consists in this, that whereas the cells in the left half are isolated and granular, those in the right half are more inflated, more transparent, and provided with buds, which may be seen in every stage of development, from their first appearance till they become as large as the parent cells. They continue to grow until they detach themselves; then they bud in their turn, so that the same figure may furnish examples of cells of the first, second, and third generations. In the right half, the protoplasm contained in the cells exhibits circular spots or vacuoles, which may be made to appear lighter or darker than the rest of the cell by slight movements of the object-glass of the microscope. These spots are due to a migration of the protoplasm towards the sides; they commonly occur in yeast cells the vitality of which, from deficient nourishment, has become suppressed—the shrivelled appearance which they then assume being due to their being forced to live upon themselves, so to speak. However, by introducing such cells into a nutritive and aerated liquid the vacuoles quickly disappear. [Illustration: Plate 7. Yeast-cells—Worn out and Dissociated (left), after Revival in a Sweet Wort (right).]