IX. A conjugating "yeast."

The organism described in this paper was obtained from commercial ginger in a flask of saccharose-Mayer solution. On keeping the flask at a temperature of 25° C., fermentation occurred, and a brownish-white deposit was formed. An examination of this deposit showed that it consisted chiefly of yeast-cells. Some of these cells were separated, and fractional series of six plate-cultures each were made. The plates were kept at the ordinary room temperature, and the colonies of yeast-cells were visible to the naked eye in three days. The colonies when a fortnight old appeared to the naked eye as small rounded white masses, about the size of a pin’s head, with regular edges. Under the low power of the microscope the edges appeared fairly regular in those colonies which had developed on the surface of the gelatine, but the submerged colonies had a woolly appearance, due to numerous branches made up chiefly of yeast-cells placed end on end, and comparatively few side branches of such cell-systems, the branches radiating out from a central mass of yeast-cells. By means of hanging-drop cultures in beer-wort gelatine a single cell was selected under the microscope, and its development watched (see Plate 46, fig. 1), until the colony to which it gave rise was large enough to be visible to the naked eye. An infection was then taken from this colony, and further fractional series in beer-wort gelatine made; a streak-culture on beer-wort gelatine being made at the same time from the same infection. From the growths which developed on these streak- and platecultures, an abundant supply of the organism in a pure state was obtained. The streak-culture was the method adopted for keeping a pure stock of the fungus.