8 THE PREPARATION OF MICROSCOPIC OBJECTS. 
! (a) Make asaturated solution of crystallized calcium chloride 
in 70 per cent. alcohol, and add alum to saturation. 
(6) Make a saturated solution of alum in 70 per cent. alcohol, 
and add (a) to (6) in the proportion of 1 to 8. 
(c) To the mixture of (a) and (b) add a few drops of a 
saturated solution of hematoxylin in absolute alcohol. 
The specimens, which must be perfectly free from all trace 
of acid, should be left in the hematoxylin in a covered vessel 
or stoppered bottle for from one to twenty-four hours, according 
to the size of the specimen and the depth of staining desired, 
and then placed in strong spirit for some hours before mounting. 
Hematoxylin stains the nuclei of cells much more strongly than 
the other parts. 
2. Borax-carmine, This, which is perhaps the most generally 
useful of all the stains in ordinary use, is prepared as follows: 
Dissolve 2 parts of carmine and 4 of borax in 100 parts of 
water: add an equal volume of 70 per cent. alcohol; let the 
mixture stand for a couple of days, and then filter. 
Specimens may be left in borax-carmine for from one to 
twenty-four hours, or even for two or three days: on removal 
they should be placed in acid-alcohol—~.e,, 70 per cent. alcohol 
to which a few drops of hydrochloric acid have been added— 
until they become a bright scarlet colour, when they should be 
transferred to 70, and then to 90 per cent. alcohol, in which latter 
they may be left till required. The time of immersion in acid 
alcohol will vary according to the nature and size of the speci- 
men from a quarter of an hour up to a day or more. 
3. Picro-carmine. A very useful, and to a certain extent a 
differential stain, as it colours the several tissues different 
tints. It may be prepared thus: Dissolve | gramme of carmine 
in 4 ce. of liquor ammonia and 200 ce. of distilled water. Add 
5 grammes of picric acid ; shake the mixture well for some 
minutes, and then decant from the excess of acid. Leave the 
decanted liquid for some days, stirring it occasionally: then 
evaporate it to dryness, and to every 2 grammes of the dried 
residue add 100 ce. of distilled water. 
Picro-carmine answers best with specimens preserved in 70 per 
cent. alcohol. They should be left in the stain for a day, and 
then placed in 70, and afterwards in 90 per cent. alcohol. Some 
specimens give better results by washing freely with water on 
