IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 215 
parations giving a dark green or blue-green colour in cell and 
nucleus after treatment with the reagent mentioned, the cells 
are found, after the prolonged application of the glycerine and 
sulphide mixture, to exhibit an iron reaction in the cytoplasm 
apart from the spherules, and a similar reaction diffused in the 
karyoplasm independent of that manifested by the chromatin 
network, the intensity of the reaction corresponding in each 
case to the depth of the green stain given these elements by 
indigo-carmine reagent. When in the advanced development 
of the larval Amblystomata the yolk-spherules disappear 
from the cytoplasm of the cells, the nuclei and all cells, except 
those undergoing transformation into striated muscle, lose their 
capacity for absorbing and retaining the indigo of the fluid of 
Shakespeare and Norris. This indicates that the yolk chro- 
matin is changed into some other compound, and the prolonged 
application of the glycerine and sulphide mixture confirms this, 
for the cytoplasm, except in secreting cells, the striated muscle- 
fibre, and in the hematoblasts and red corpuscles, is destitute 
of iron compounds, while the nuclei give, much more slowly, 
and apparently with greater difficulty, a reaction for iron which 
is, in contrast with what is observed in the earlier stages, con- 
fined to the nuclear network and nucleoli. The iron-containing 
substance is transferred to the nuclei, and with this transfer- 
ence the iron becomes more firmly combined—a process the 
very reverse apparently of that which is illustrated in the 
formation of the yolk-spherules, for the iron compound of the 
latter, though derived from the nucleus of the ovum, is less 
firmly combined than that of nuclear chromatin giving origin 
to it. 
The yolk-spherules of the hen’s egg, as is well known, have 
characters differing from those of Amphibian ova, but the most 
marked difference consists in the distribution of the iron-con- 
taining compound. The yolk-spherule in the ova of Ambly- 
stoma and Necturus is homogeneous, and the iron compound 
is uniformly distributed through it ; but in the hen’s egg ele- 
ments of this character are to be found only in the constituents 
of the “ white” yolk and in some of the “ yellow” spherules in 
