t, but in a
characteristic manner, a special kind of cell, _e.g._ the eosinophils,
mast cells, or bacteria. Single staining is attained on the principle of
maximal decoloration. (Cp. E. Westphal.)

Finally, we have panoptic staining; that is, by methods which bring out,
as characteristically as possible, the greatest number of elements.
Although we must use high magnifications with these stains, we are
compensated by a knowledge of the blood condition that cannot be reached
in any other way. A double stain is generally insufficient, and at least
three different dyes are used.

Successive staining was formerly used for this purpose. But everyone who
has used this method knows how difficult it is to get constant results,
however careful one may be in the concentration and time of action of
the stain.

Simultaneous staining offers undoubted and important advantages. As
there is much obscurity with regard to the principle on which it rests
we may here shortly explain the theory of simultaneous staining.

We will begin with the simplest example: the use of picro-carmine, a
mixture of neutral ammonium carmine and ammonium picrate. In a tissue
rich in protoplasm, carmine alone stains diffusely, though the nuclei
are clearly brought out. But if we add an equally concentrated solution
of ammonium picrate, the staining gains extraordinarily in distinctness,
in as much as now certain parts are pure yellow, others pure red. The
best known example is the staining of muscle with picro-carmine, by
which the muscle substance appears pure yellow, the nuclei pure red. If,
however, instead of ammonium picrate we add another nitro dye which
contains more nitro-groups than picric acid, for example the ammonium
salt of hexa-nitro-diphenylamine, the carmine stain is completely
abolished, all parts stain in the pure aurantia colour. The explanation
of this phenomenon is obvious. Myosin has a greater affinity for
ammonium picrate than for the carmine salt, and therefore in a mixture
of the two combines with the yellow dye. Owing to this combination it is
not now in a condition to chemically fix even carmine. Further, the
nuclei have a great affinity for the carmine, and therefore stain pure
red in this process. If, however, nitro dyes be added to the carmine
solution, which have an affinity for all tissues, and also for the
nuclei, the sphere of action of the carmine becomes continually smaller,
and finally by the addition of the most power