562 Humphrey . — On some 
greatly increased, the best staining methods will offer the 
only trustworthy means for their study. We know certain 
combinations which give to the nucleoli in all stages a sharply 
differential colour by which they can be unhesitatingly dis- 
tinguished from all other bodies in the cell. They vary 
greatly, as is well known, in form, size, and position in the 
nucleus, and sometimes, as Zimmermann has shown, outside 
of it. But, so long as they are present in size recognizable 
by the highest powers, their reaction with certain stains 
remains characteristic. A favourite combination with many 
students for differentiating the chromatic and nucleolar ele- 
ments of the nucleus has been the mixture of fuchsin and 
iodine green, first recommended by Babes and introduced 
into botanical technique by Strasburger. This combination 
was used by Zimmermann in his studies, with the addition of 
an after-treatment of the sections with alcohol containing 
iodine and acetic acid. This addition constitutes a real 
improvement in the process by increasing the sharpness of 
the preparations obtained, and the permanence of the stain. 
The nucleoli take, under this treatment, a blood-red colour, 
which is not approached by that of any other cell-constituent. 
Zimmermann’s argument is based on the occurrence of 
nucleolar masses outside of the nucleus during karyokinesis, 
a fact which no one will dispute. Several years before his 
observations, very large and numerous nucleolar masses had 
been observed by Strasburger in the cytoplasm of the wall 
layer of the embryo-sac of some Amaryllidaceae, and 
Zimmermann has done good service in showing that the 
phenomenon is more common than had previously been 
suspected. He has found the ‘ extranuclear nucleoli’ to be 
sometimes abundant in the cytoplasm of cells from a large 
number of tissues, both during nuclear division and in the 
resting-state. But he attempts to show that the nucleoli are 
normally thrown out of the nucleus during division, remaining 
in the cytoplasm, entire or in fragments, and being taken up 
again by the daughter-nuclei resulting from the division. 
He regards the nucleoli as true organs of the nucleus derived 
