- 
a] y be prepared by simply adding an equal volume of r 
396 The Study of Zoölogy in Germany. [July, 
twenty-four hours. The soap does not become hard until the 
alcohol evaporates from it; the less alcohol, therefore, put in 
originally, the better. The soap ought to remain perfectly clear, 
enabling one to see the imbedded specimen within, so that it can 
easily be observed exactly in what plane every section is made, 
which is not possible when paraffine or wax is used. The sec- 
tions, when made, if cut in soap, must be put in alcohol, if from 
paraffine, in spirits of turpentine, to dissolve out the remains ọf 
the imbedding mass. 
If now the sections, after being thus freed from the adherent 
foreign matter, be mounted directly, they make poor prepara- 
tions; the single parts are indistinct, and the whole is very trans- 
parent. This can be avoided by coloring them. It may be 
safely asserted that the introduction of staining fluids, by Gerlach, 
in 1858, was the most important step in advance ever yet made 
in histological technic. Coloring matters, as regards their action 
on cells, belong to two classes : either they produce a diffuse color- 
ing of the whole cell, or they stain the nucleus much more deeply 
than the protoplasm and the membrane of the cell. The prin- 
cipal are dyes of the latter class, carmine, hæmatoxiline, and ani- 
line blue, which are esteemed in the order named. The two for- 
mer are invaluable, for by marking out the nuclei so distinctly 
they enable us to recognize so many centres of cells, and to ob- 
serve characters which have been made prominent by their color- 
ation, and are very different in the various forms of cells. In fact, 
přťparations for the microscope cannot be felt or dissected, but 
only seen; therefore, the differential coloring produced by car- 
mine, for example, is an assistance to the eye, comparable to the 
raised alphabets of the blind. In both cases, the conditions 
under which the special sense, whether sight or feeling, has to 
act are greatly exaggerated, so to speak, thus producing magni- 
fied or strengthened perceptions. 
Carmine is by far the most generally useful. It is employed 
in various solutions, the recipes for which may be found in va- 
rious hand-books, and need not, therefore, be quoted in this 
article. The first step in preparing it is to dissolve some of the 
: fine-powdered carmine in a small quantity of ammonia, and it . 
may be used at once in that form after allowing the superfluous 
ammonia almost entirely to evaporate. A very excellent — 
l ather 
` strong acetic acid to the dissolved carmine ; the exact proportion 
is not of very great import. Beale’s carmine keeps a long time 
