THE MICROTOMIST' S VADE-MEOUM

than can be extracted by any process hitherto employed for the
preparation of carmine for histological purposes."   .
It is not certain whether the stain of carminic acid is stable  IS
in glycerin. " Some preparations coloured in alcoholic car-
minic acid and then put up in glycerin lost their colour in a
few months, while similar preparations mounted in Canada          5Rt th
balsam   retained their colour perfectly."    But the author
thinks this may have been due to impurity of the glycerin        s
employed. givii
For another mode of preparation of carmine see Picro-           lh4fer
carmine, Pergens' formula, No. 70.
49. Carmine Stains in General.-Carmine was at first            qUe
employed in histology in the form  of ammoniacal solutions;       Ta1 0
and various mixtures made on this principle are still used.      thle ior
It was, however, at length clearly seen that the use of the       solutio1ns
ammoniacal solutions had two serious disadvantages; firstly,     tha ilk
the above-mentioned instability of the solutions, which from      60liiiou,
the very moment of their formation are engaged in a series of     Bb , 1
ill-understood chemical processes that makes it impossible for    anaeit1
the anatomist to know whether at any moment his solution is       acj sti
in a state fit for producing a good stain; and, secondly, the     diVideii
fact that the free ammonia of the solutions has a highly Thdol
injurious action on many delicate tissue elements. The diver-     staiS
sity of the many formuhe for carmine staining fluids given         beig i
below is in great part the result of attempts to find solutions    case
that should be stable and should not contain free ammonia.         gaer
Such are the neutralised ammoniacal solutions of Betz, Heid- MoUtic
enhain, and Hoyer; such is the celebrated picro-carmine of         don by
Ranvier, and such are the alum-carmine and borax-carmine of        mUeta(
Grenacher.                                                         Wof,
The especial value of carmine lies in its property of readily   percet
affording a nuclear or protoplasmic stain.     This property       frriA
was explained by Beale by means of the hypothesis that              Ths
recently dead protoplasm has an acid reaction. " Hence if an        finul
alkaline solution of colouring matter from which the colour         Ilis

46


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