IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 219 
Apart from the question of the occurrence of fat in such 
elements, there may be no doubt about the intimate associa- 
tion of the iron-containing substance and the fat in the 
spherules. Owing, however, to the size of the latter, as well 
as to the density of the coagulated material in them, the osmic 
acid used to demonstrate the fat penetrates but slowly, and 
when, as usually happens, fat droplets stud the periphery of 
the spherule, little or none of the reagent reaches its interior, 
which then has only a straw-yellow colour. If, however, a 
few spherules, coagulated with heat, are kept in a quantity of 
Flemming’s fluid for twenty-four hours, the osmic acid pene- 
trates the spherules in some cases and causes their granules 
to become brownish-black, a fact which can be most distinctly 
observed when the cover-glass is pressed down sufficiently to 
disintegrate the spherules and set the granules free. If the 
granules are large, the occurrence of fat in them is much less 
readily demonstrated, possibly because the density of such 
elements prevents penetration on the part of the osmic acid. 
These granules are undoubtedly the source of the greater 
part of the iron-holding nuclein isolated by Bunge from the 
yolk,! since the “white” yolk is comparatively small in 
amount. Miescher? regarded the nuclein, which he separated 
from the yolk, as only in part localised in the homogeneous 
spherical elements in the “white” portion, and he believed 
that the greater part of it was derived from the granules in 
the “‘ yellow ” spherules, and that none of it exists in a dissolved 
form, a conclusion fully supported by the facts concerning the 
localisation of the iron. 
In describing the transference of the chromatin of the 
spherules from the cytoplasm to the nucleus of each cell of the 
larval Amblystoma, reference was made to an exception in 
the case of developing muscle-fibre. In the cells undergoing 
transformation into striated fibres, some of the chromatin dis- 
solved in the cytoplasm finds its way into the nuclei as in other 
1 « Ueber die Assimilation des Hisens,” ‘ Zeit. fiir Physiol. Chemie,’ vol. ix, 
p. 49, 1885. 
2 «Die Kerngebilde im Dotter des Hihnereis,” ‘ Hoppe-Seyler’s Med.- 
Chem. Untersuchungen,’ 1871, p. 502. 
