IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 209 
with a cover-glass, kept for days ina warmoven. This method 
must be resorted to in order to get the iron reaction, since other- 
wise the large nuclei may be kept for a month in contact with 
the reagent in the warm oven without resulting in demon- 
strating, in the slightest, any iron reaction. In the peripheral 
nucleoli, when they are present, the amount of the iron, as 
indicated by the depth of the reaction, is great, but in the 
remaining elements of such nuclei it is small. When such 
preparations are examined with a strongly magnifying objective, 
the chromatin network, as revealed by the iron reaction given, 
is found to be less distinct, and instead of granules of iron- 
holding substance arranged at definite positions along the 
course of the fibrillz, as in ova much less developed, the iron 
is now seen to be chiefly confined to beadlets, few in number, 
sometimes regularly, sometimes irregularly, disposed on the 
fibrille, which, in ammonium hydrogen sulphide preparations, 
manifest but a feeble greenish tint. There is an inverse rela- 
tion between the size of the nucleoli and the amount of the 
chromatin in the network, and an examination of some nuclei in 
which the formation of the peripheral nucleoli has commenced, 
and of those in which the development of these bodies is much 
more advanced, irresistibly suggests that the latter are derived 
from the chromatin of the network. I have elsewhere! pointed 
out that the solution of the substance of which these nucleoli 
are composed and its diffusion from the nucleus into the cyto- 
plasm of the ovum are connected with the formation of the 
yolk-sperules in Amphibia. That a solution of the peripheral 
nucleoli takes place has been noted by O. Schultze? and Born. 
Schultze found that with the solution of the nucleoli (keim- 
korperchen) the contents of the nucleus and the substance sur- 
rounding the latter were affected in the same way by reagents 
and staining fluids, and he believed that the dissolved sub- 
1 «Transactions of the Canadian Institute,’ Toronto, vol. i, part 2. 
2 “Untersuchungen tber die Reifung und Befruchtung des Amphibieneies,” 
‘Zeit. fiir wiss. Zool.,’ vol xlv, p. 177. 
$ “Die Struktur des Keimblaschens im Ovarialei von Triton taeniatus,” 
‘Arch, fir Mikr, Anat,,’ vol. xliii, p. 1. 
