mixtures containing three
and more colours. Theoretically there are two possibilities for such
combinations:

1. Staining mixtures of 1 acid and 2 basic dyes,

_e.g._ orange--amethyst--methyl green;
narcein--pyronin--methyl green;
narcein--pyronin--methylene blue.

2. Staining mixtures of 2 acids and 1 base, in particular the mixture to
be described later in detail of

orange g.--acid fuchsin--methyl green.
Further narcein--acid fuchsin--methyl green,

and the corresponding combinations with methylene blue, and amethyst
violet may be mentioned.

The importance of these neutral staining solutions lies in the fact that
they pick out definite substances, which would not be demonstrated by
the individual components, and which we therefore call =neutrophil=.

Elements which have an affinity for basic dyes, such as nuclear
substances, stain in these neutral mixtures purely in the colour of the
basic dye; acidophil elements in that of one of the two acid dyes;
whilst those portions of tissue which from their constitution have an
equal affinity for acid and basic dyes, attract the neutral compound, as
such, and therefore stain in the mixed colour.

* * * * *

The eosine-methylene blue mixtures are exceptional in so far, that it is
possible with them, for a short time at least, to preserve active
solutions, in which with an excess of basic methylene blue, enough eosin
is dissolved for both to come into play. A drawback however of such
mixtures is, that in them precipitates are very easily produced, which
render the preparation quite useless. This danger is particularly great
in freshly prepared solutions. In solutions, such as Chenzinsky's, which
can be kept active for a longer time, it is less. Hence fresh solutions
stain far more intensely and more variously than older ones, and are
therefore used in special cases (see page 46). If the stain is
successful the appearances are very instructive. Nuclei are blue,
haemoglobin red, neutrophil granulation violet, acidophil pure red, mast
cell granulation deep blue, forming one of the most beautiful
microscopic pictures.

For practical purposes, besides the iodine and iodine-eosine solution
described below (see page 46) the following are especially used:

1. =Haematoxylin solution with eosin or orange g.=

Eosin (cryst.) 0.5
Haematoxylin 2.0
Alcohol