Most of the structures which have been described in yeast cells can be made visible in the living cell with an ordinary light microscope.
Many of the structures in yeast cells can be stained in temporary liquid mounts of unfixed cells by control of pH, oxidation-reduction potential and the ratio of cell concentration to the concentration of dye. All these factors are interrelated and altering one may require a change in another to obtain the most effective result. The preparations can be be freeze-dried and held for about a week for critical observation.
At pH 8.1 filamentous structures inside the vacuole similar to those in unstained cells can be observed. At pH 11, the chromatin appears to disperse and to be precipitated on the wall of the vacuole. The precipitate subsequently peels off and appears as a tightly rolled tube moving freely in the vacuole. In cells with lobed vacuoles, the dispersed chromatin is equally distributed between the inter-communicating lobes and a “Peeling” from the wall appears in each lobe.
When a solution of toluidine blue is allowed to dry slowly on a slide, long, thick, dark blue crystalloids are formed on evaporation of the solvent. The shape of the structure which appears in the vacuole may be influenced by the tendency of toluidine blue to form long, thick crystalloids, but, since the structures are almost invariably double, it appears that the crystalloidal structure of toluidine blue is not the only factor influencing their form. Toluidine blue stains the intravacuolar structures under conditions when metaphosphate is present in the cell.
No birefringent structures are visible in the unstained yeast cell. The chromosome complexes stained with toluidine blue are spectacularly birefringent although the centrochromatin similarly stained is not.