Hatal, Mitosis in Nerve Cells. 293 
the frog as composed of oxychromatin in very abundant quan- 
tity and small amount of basichromatin. He also said that the 
nucleolus is composed of a substance very similar to the baso- 
phile substance of the nucleus, but not identical with it. 
TIMOFEEW’' observed two kinds of nucleoli in the nucleus 
of the nerve cells of birds, one of which exactly corresponds in 
its structure to that described by Levi; while the other is en- 
tirely acidophile. 
VI. Critique of the observations of previous authors on the 
nucleolus. 
From the above descriptions, we can distinguish two en- 
tirely different views concerning the structure and staining reac- 
tions of the nucleolus. One of these is represented by Lev, 
who regards the nucleolus as composed of two substances, baso- 
phile and acidophile. The other is represented by Cayjat and 
VAN GEHUCHTEN, who believe the nucleolus to be merely a 
modification of the basophile substance, which has resulted 
from long mitotic repose. 
In the analysis of the cells by histological methods, it is 
evident that these methods which give the highest degree of differ- 
entiation are the ones which should be made the basis of our 
description. Hence we are justified in following the descrip- 
tions of those authors who have been able to obtain the highest 
degree of differentiation in the cells which they studied and in 
disregarding the views which have been developed on the basis 
of negative results. 
The results obtained by Rosrn, who states that the nucle- 
olus and nucleus are neutrophile are, no doubt, due to the less 
differentiation of the stains which were employed by him. 
The present writer also questions the conclusions drawn 
by CajAL and vAN GEHUCHTEN, because these investigators 
used only methylen-blue after Nisst. By this method it is ab- 
solutely impossible to distinguish the different substances in the 
1 TIMOFEEW: Beobachtungen iiber d. Bau der Nervenzellen d. Spinalgan- 
glien u. d. Sympathicus beim Vogel. Internat, Monatschr. f. Anat. u. Physiol., 
1898, H. 9. 
