COCHINEAL STAINING SOLUTIONS                73
t     The stain is not so powerful as ammonia carmine or
Kleinenberg's humatoxylin or Grenacher's alcoholic carmine.
In general, however, Mayer prefers it to all other stains, and
only uses Kleinenberg's huematoxylin in special cases.
Alcohol of 70 per cent. is not the only strength by means
of which the colouring matters of cochineal may be extracted.
But extracts obtained by means of 90 per cent. or absolute
alcohol, are very weak in colour, and are further useless
o 0because they yield a diffuse stain. The weaker the alcohol
the stronger the extract of colouring matter; and extracts
a   made by means of 50 per cent. or 60 per cent. alcohol would
be preferable to that obtained by means of the 70 per cent.
alcohol, were it not that they are naturally more deficient in
i   penetrating power.
88. Alum Cochineal (Partsch's formulal).-Powdered cochi-
neal is boiled for some time in a 5 per cent. solution of alum,
4 the decoction filtered, and a little salicylic acid added to pre-
serve it from mould.
89. Alum Cochineal (Czoker's formuld2). -Seven gr. cochineal
and 7 gr. calcined alum are rubbed up together into powder
in a mortar, add 700 gr. distilled water, and boil down to
400 gr. When cool, add sufficient carbolic acid to be per-
ceptible by the smell, and filter several times. The violet
solution is ready for use, and will keep for six months, after
i)  which time it must be filtered again, and a fresh trace of
carbolic acid added.
This stain possesses considerable elective faculty, and is
stated to stain, in a longer or shorter time, all kinds of tissue,
a ,   no matter in what way they may have been hardened. Nuclei
PL  are stained humatoxylin-colour, and other elements different
ills  tones of red, so that the effect is that of a double stain with
1q.   humatoxylin and carmine. Alcohol objects require three to
five minutes, chromic objects three to five hours. The author
S' Arch. Mik. Anat.,' xiv (1877), p. 180.
2 'Arch. Mik. Anat.,' xviii (1880), p. 413.