NERVE TERMINATIONS OF THE TADPOLE. 57 
number of layers was accompanied by other changes, which 
will be referred to farther on. I think that these points are 
important, for some of the results of Pfitzner’s researches might 
be accounted for on the ground that he used material which 
was in such abnormal conditions. 
IlJ.—Meruops or Srtupy. 
For the purpose of hardening the epithelium for vertical 
sections Erlicki’s fluid and solutions of chromic acid of dif- 
ferent strengths were employed. The former reagent is not 
suitable for anything else than preserving well the outlines of 
the cells and for the figures of Eberth, to which it gives a full 
plump appearance. It is of no value for karyokinetic figures, 
which, after its use, have the appearance of a scattered granu- 
lation, and it renders the intercellular bridges invisible. For 
preparing these, as Pfitzner recommends, chromic acid is the 
best reagent, especially when used of the strengths of one sixth 
and one third of 1 per cent. For the figures of Eberth, how- 
ever, it has not in my hands proved as suitable as Erlicki’s 
fluid. 
For staining the figures of Eberth nigrosine is to be specially 
recommended, because it gives to them a deep dark-blue colour, 
while the epithelial cells and their nuclei take but a very slight 
shade. In this way most of the finer processes of a figure can 
be followed throughout a cell. Saffranine is also to be recom- 
mended, as it gives a deep stain to the figures, but it has one 
disadvantage compared with nigrosine, in that it is difficult to 
get a successful preparation with it without at the same time 
obtaining the cell protoplasm more or less diffusely stained. 
In order to obtain sections stained with both nigrosine and 
saffranine the following method was adopted :—The tail of the 
specimen, hardened in Erlicki’s fluid, and the reagent extracted 
with weak, then with strong alcohol, is put for thirty or forty 
hours in a solution of nigrosine, made by dissolving 0°71 grm, 
of the latter in 4 cc. of distilled water and adding this to 96 
cc. of strong alcohol. The excess of the nigrosine is extracted 
with alcohol, and from the tissue embedded in paraffin vertical 
