56 Wager and Penis ton.—Cytological Observations on 
sap in proportion to the very diffuse nuclear network, that failure to recog¬ 
nize it as a nucleus is perhaps not astonishing. But the extraordinary 
activity of the yeast cell at certain stages in its development explains the 
unusual size of the nuclear vacuole, and in the light of the large vacuolar 
nuclei usually associated with gland or other cells which exhibit very 
active metabolism, affords an additional proof of its nuclear nature. 
It is only under favourable conditions that the nuclear network can 
be clearly seen. Its appearance under the microscope varies with the 
number, size, and staining capacity of the granules present on the net¬ 
work, and the density and staining capacity of the cytoplasm. The most 
cursory examination of yeast cells shows that the chromatin granules 
vary considerably in size and arrangement. They are sometimes com¬ 
paratively few in number (Fig. 105) and large (Figs. 59, 116), at other times 
smaller and more numerous (Fig. 109). They are sometimes arranged 
with remarkable regularity (Figs. 102-4), but usually they are unevenly 
distributed on the network. From time to time both the granules and 
the cytoplasm show marked differences in their behaviour to nuclear 
stains according to the conditions which obtain in the cell. In the 
early stages of fermentation the chromatin network (vacuole) occupies 
about a third of the space in the cell. Granules are present on the 
threads, but are not particularly conspicuous, and are rendered less so 
by the surrounding cytoplasm, which under these conditions is deeply 
stainable, as is also the nucleolus. The interior of the vacuole is appa¬ 
rently occupied by watery contents, which remain unstained, and in sharp 
contrast to the rest of the cell. It is clear that in this condition the 
chromatin network will not be readily seen, owing to its peripheral arrange¬ 
ment and consequent close proximity to the deeply stained cytoplasm, 
and at first sight the cell will appear to contain merely the deeply 
stainable body and simple vacuole surrounded by cytoplasm, as described 
by the majority of observers, who have apparently based their conclusions 
on cells in the early stages of fermentation. As fermentation continues 
the cytoplasm loses its capacity for nuclear stains, and the network becomes 
conspicuous, partly because of the increased transparency of the cytoplasm 
and partly because of the increase in the number of chromatin granules. 
The vacuole continues to occupy more and more space until, near the 
height of fermentation, it practically fills the entire cell (Figs. 17-19, 
104). At this time the nucleolus stains feebly, but the granular sub¬ 
stance at its periphery stains intensely. Immediately after the period 
of highest fermentation is passed, the chromatin network decreases until 
it occupies a comparatively small space, frequently much smaller than 
in the early stages of fermentation (Figs. 110, 140-5). This decrease 
precedes the sinking of the cells in the liquid, and, as we shall see 
later, is coincident with the increase of glycogen. In some cells, and 
