70 Wager and Peniston.—Cy to logical Observations on 
to the haematoxylin only. The colour both of the cytoplasm, granules, 
and nucleolus was light slaty blue. The nucleolus was, however, slightly 
more deeply stained than the surrounding cytoplasm. In compressed yeast 
the granular substance at the periphery of the nucleolus was more deeply 
stained than the nucleolus (Figs. 152-6). The chromatin network in the 
vacuole was only slightly stained, a few granules here and there on the net¬ 
work showing a deeper coloration. In some cases the central volutin granule 
or granules in the vacuole gave a distinct reaction for iron (Figs. 154-6). 
These observations confirm Macallurn’s conclusion, therefore, that 
in Saccharomyces the cytoplasm gives a diffuse reaction for f masked ’ iron, 
and that in addition to this there is a distinct reaction for it in the homo¬ 
geneous nucleolus, nucleus, nuclein body, or corpuscule of various observers. 
Phosphorus. 
The chemical constitution of the various elements of the living cell can 
only be inferred indirectly from micro-chemical reactions upon cells killed 
in various ways and from the chemical analysis of dead cells. The con¬ 
clusions obtained from analysis of dead cells are complicated by the fact 
that we cannot isolate the separate elements of the cell for examination. 
It has been shown, however, that digestive fluids dissolve certain portions 
of the cell contents, and that among those that are least acted upon is the 
nucleus, and especially the deeply stainable portion of it known as the 
chromatin. Kossel, taking advantage of this, found that the part of the 
cell which remains undigested contains a certain substance which gives on 
analysis about 6 per cent, of phosphorus. Meischer investigated the 
spermatozoa of the salmon, which contain large nuclei and very little 
protoplasm, and succeeded in isolating an albumin containing phosphorus 
which formed 50 per cent, of the whole, the phosphorus present being 
about 10 per cent. He came to the conclusion that phosphorus was present 
in the nucleus, and called the substance containing it nuclein. 
The localization of phosphorus in the cell is of great importance 
in cytological investigation, for although other substances such as lecithin 
and zymogen are found to contain it, nuclein is the substance chiefly rich in 
phosphorus. It is evident, therefore, that in small cells in which the details 
of structure are not well marked, the presence of phosphorus, taken in 
conjunction with the results obtained from various reagents and stains, may 
be of great value in the identification of the nucleus or of nuclear elements. 
The methods of gross analysis adopted by Meischer, Kossel, and others 
are not suitable for this purpose ; it is necessary to obtain some micro¬ 
chemical method in order to determine exactly which parts of the cell con¬ 
tain phosphorus. The most delicate test for phosphorus is the yellow 
precipitate which is produced by ammonium molybdate in the presence 
of nitric acid. This precipitate is very abundant even when there is only 
