58 Wager and Penis ton.—Cytological Observations on 
of changes observable is, however, fairly definite, and the explanation may 
be offered that food material absorbed into the nuclear vacuole is there 
elaborated into chromatin by means of the nuclear network and possibly 
the nucleolus; and may then be extruded into the cytoplasm, either 
as chromatin or in a slightly different form, to take part in the various 
formative and other activities which are associated with the cytoplasm, and 
more especially perhaps in the production of enzymes. 
4 
b. The Nucleolus. 
The nucleolus is a homogeneous, spherical or oval body in close con¬ 
tact with the nuclear vacuole. 1 It consists of a substance closely resembling 
the plastin of the nuclei of higher organisms and has very little affinity for 
nuclear stains. Under certain conditions which may obtain in the yeast 
cell, it becomes more or less impregnated with a chromatin-like substance 
which stains deeply. 
There is also present at the periphery of the nucleolus a granular sub¬ 
stance which stains intensely with Heidenhain’s iron-alum haematoxylin, 
and remains strongly differentiated when every other part of the cell is de¬ 
colourized. This substance, which resembles chromatin, often occurs in the 
form of a single large granule or a number of small ones (Figs. 49-80), and is 
so closely associated with the periphery of the nucleolus that it is difficult to 
determine from an ordinary preparation whether it is actually contained 
within the nucleolar substance or is merely in close contact with its surface. 
Instructive results with regard to the structure of the nucleolus and its 
morphological relation to this deeply-stained chromatin were obtained by 
squeezing out the contents of a number of yeast cells. 
The yeast used for this purpose was stained en masse in Heidenhain’s 
haematoxylin, the times for mordaunting and staining being proportionally 
prolonged to ensure more precision in the subsequent washing-out pro¬ 
cesses. When the cells were sufficiently differentiated, they were well 
washed in water and transferred to dilute glycerine. A few cells were then 
placed on a slide and the contents expressed by means of sharp taps on the 
cover-glass. The nucleolus was thus, in many cases, separated from the 
other cell contents, and was clearly visible as a homogeneous body and not, 
as many observers state, a nucleus and enclosed nuclear sap. 2 The peri¬ 
pheral chromatin was clearly shown in many cases around the nucleolus, 
1 Guilliermond (’02) states that the nucleus (nucleolus) possesses the normal structure of 
a nucleus, with membrane, network, etc., and that it appears homogeneous only in badly fixed and 
stained or anomalous specimens of S. cerevisiae. But in the cells figured in his coloured Plate X, 
all the nuclei (nucleoli) are shown as homogeneous bodies, just as figured by Wager (’98). It is not 
clear to us why the author should have chosen badly stained or anomalous specimens for this purpose. 
2 We are not prepared to say that this homogeneous body (nucleolus) does not under some con¬ 
ditions become more or less vacuolated. Certain appearances observed in compressed yeast lead us 
to suspect that this may take place occasionally. 
