216 A. B. MACALLUM. 
the most peripheral layers of the yolk, while in all the other 
spherules the distinctive feature is the disposition of the iron 
compound in a finely granular form. This cannot be deter- 
mined with fresh yolk, for when treated with ammonium 
hydrogen sulphide the greater part of it dissolves, and the solu- 
tion becomes dark green owing to the formation of sulphide of 
iron. Under the microscope no formed elements can be ob- 
served in such a preparation, except those derived chiefly from 
the ‘‘ white’’ region, and it is not possible to ascertain, under 
these conditions, the relations of the iron-holding nuclein in 
other parts of the yolk. Another difficulty experienced in 
dealing with fresh uncoagulated yolk is that, when removed 
from the egg the spherules disintegrate, the granular contents 
escaping and obscuring more or less the characters of the other 
elements. To avoid this the substance of the spherules must 
be coagulated, and to accomplish this satisfactorily I placed 
the eggs in boiling water for ten minutes. Thespherules were 
thus fixed in polyhedral form, and, after these had lain in strong 
alcohol for several days, it was an easy matter to determine the 
distribution of the iron in them. 
The results obtained were according to the variety of spherules 
examined. In those known as “ white” the reaction for iron 
was very distinctly obtained, but it was wholly confined to 
their homogeneous spherical bodies. The reaction is, imme- 
diately after the application of the glycerine and sulphide 
mixture, light green, but this becomes deeper after a few days, 
when the preparation is kept at a temperature of 60° C. The 
homogeneous elements undoubtedly contain a quantity of 
nuclein, for they resist the action of artificial gastric juice and 
dissolve in weak alkalies, while they constitute the only part of 
the “ white” spherules that possesses, like chromatin, the pro- 
perty of absorbing and retaining colouring matters. This was 
found to be the case specially when the spherules, coagulated 
by heat, were further treated with Flemming’s chrom-osmio- 
acetic mixture for twenty-four hours, then with alcohol, and 
finally with a solution of safranin. When the excess of the 
stain was extracted with alcohol and the spherules mounted in 
