72 
Wager and Penis ton.—Cytological Observations on 
are slightly yellow. The preparations, after washing, can be dehydrated 
and mounted in balsamin the usual way. Good results were obtained from 
cells mounted whole, but the best differentiation was seen in sections cut 
in paraffin by means of a microtome. 
We found that many photographic reducing agents, such as eikonogen, 
amidol, quinol, etc., can be used to bring about the change in colour of the 
precipitate, but they are not very satisfactory, as the results are confused by 
a brownish-yellow coloration of the cell contents. Nevertheless, when the 
distribution of phosphorus has been generally determined by means of 
phenyl-hydrazin, they are very useful. 
The phosphorus reactions at various stages in the growth of the yeast 
cells have been carefully followed in N. cerevisiae , I. Hansen, which was 
obtained in a pure culture from Mr. Murphy. It was grown in wort 
and fixed in absolute alcohol at definite intervals throughout fermentation. 
We find that when a small nuclear vacuole is present, during the early 
stages of fermentation in young cells, the phosphorus is diffused throughout 
the cytoplasm and nucleolus, the granules at the periphery of the latter 
showing a marked reaction. 
As the vacuole increases in size during the progress of fermentation the 
phosphorus disappears almost entirely from the cytoplasm, but a more pro¬ 
nounced reaction for it becomes visible in the nucleolus and nuclear vacuole 
(Fig. 119, 128, 129), and in the granular substance at the periphery of the 
nucleolus (Figs. 123, 127). The volutin granule or granules near the centre 
of the vacuole are also found occasionally to give the phosphorus reaction 
(Figs. 129, 13 °)- 
The evidence thus obtained of the distribution of the phosphorus- 
containing element supports the conclusion, already arrived at on the 
grounds of their structure and staining reactions, that the vacuole and 
homogeneous body attached to it constitute the nucleus of the yeast cell. 
We find that the phosphorus reaction corresponds with the intensity of 
the haematoxylin staining, and both being more strongly marked in the 
substance at the periphery of the nucleolus, this must therefore be con¬ 
sidered to contain the greatest proportion of nuclein. 
Phosphorus begins to be prominent about fourteen hours after the 
commencement of fermentation, and appears to increase steadily up to 
from thirty-three to forty-eight hours, after which it decreases. 1 
There appears to be no inorganic phosphorus in the yeast cell. 
Specimens were placed in ammonium molybdate solution for ten or fifteen 
minutes, at 30-35° C., and after washing in water were placed in the phenyl- 
] These observations were made upon a series of pure yeast cultures set up and preserved by 
Mr. J. H. Murphy of Leeds. We hope that we may be able jointly with him to make a more 
complete investigation of the variation in the amount of phosphorus present in the nucleus under 
different conditions. 
