70           THE MICROTOMIST'S VADE-MECUM
CHAPTER VIII.                            o be
COCHINEAL STAINING SOLUTIONS.                    ai,
86. Cochineal.- Cochineal appears to have been first recoi-
mended as a staining agent by Partsch in 1877. He employed    P,
a solution of cochineal in an aqueous solution of alum. A
similar formula was again recommended by Czoker in 1880.
The formula known as Klein's cochineal fluid (which appears    Theo
to have been first published in the 'Ann. and Mag. Nat. Hist.,'
viii, 1881, p. 232) is identical with that of Czoker. These    e
fluids greatly resemble alum-carmine in their properties, So
especially in their great selective faculty. It is probably in  i
this point that their chief superiority to alum-carmine is to    t
be found. An important improvement was effected in 1878        thade
by the discovery by Paul Mayer of the properties of the 1t
alcoholic tincture of cochineal. This preparation puts into    o
our hands a stain that is as precise, as penetrating, and as
little hurtful to tissues as Kleinenberg's huematoxylin; whilst  F R1
it has the advantage of being more durable, and above all, of PC''
being the easiest to prepare of all staining fluids. Indeed, SW
almost the only point in which it proves inferior to humatoxy.  Ma0
lin and to some carmine fluids, is that it does not in all cases eela
afford a sufficiently powerful stain. (It is not known whether thinst
it is permanent in glycerin and similar mounting mediums.      61a
I am inclined to doubt its being so; I found some prepara-      ks
tions mounted in acidulated glycerin became destroyed by nis
fading of the colour in a very short time.)
The alcoholic solution of cochineal possesses a very great
selective power. Some tissue elements are stained red, others
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