THE MICROTOMIST' S VADE MECUM

159. Alcoholic Eosin (Fischer's formulac).-If an aqueous
solution of eosin be treated with acids, the free colouring
matter is thrown down, and may be separated by filtration,
and dissolved in 20 to 30 parts of alcohol (absolute alcohol is
best). A few drops of this solution are added when required
for staining to a watch-glass of alcohol.
The alcoholic solution of the free eosin colouring matter is a
generally preferable to the aqueous solution of the potassium     a
salt, and especially so in the case of preparations that have Iad
been hardened in Mfiller's solution. For in this case the        done
chromic acid of the bichromate of potash throws down the          h
free colouring-matter of the eosin in the form  of a red pre-
cipitate that can only    be kept soluble in     concentrated    5
alcoholic solution. If it is desired to use the solution of the  hntiC
potassium  salt, therefore, the chromic acid must first be       solutil
neutralised by addition of some alcali.                          l6
Both these solutions are stable. Fresh preparations stain      "o
better in the alcoholic than in the aqueous solution. The        bl
axis cylinder of nerves stains deep rose-red, whist the myelin   ad
is hardly coloured at all. Muscle stains deeply. Like the         he
first, a diffuse stain.                                           but
160. Alum-Alcoholic-Eosin.-Free eosin 1 part, alum        1    queo
part, absolute alcohol 200 parts. Not superior to the latter     oblja
formula.                                                         of a
161. Ammonia-Eosin     (Lavdowsky's formula2).-Eosin      is   dj1
dissolved in ammonia, which is allowed to evaporate, and the      both
solution is then diluted with water. It should be neutral or     is R(
very feebly alkaline. One or two drops of this are diluted        1h
with water until the mixture appears barely coloured in a          thl
watch-glass placed on a white background. The sections are        A
placed in this watch-glass and removed therein to a desiccator
(or placed under a glass shade) containing a watch-glass of      ic
1 'Arch. Mik. Anat.,' xii (1875), p. 349.
'Arch. Mik. Anat.,' xiii (1876), p. 359.

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