8 THE Microscope. 
The color reactions of these cochineal tinctures on tissues 
are very delicate and easily influenced by the preliminary or 
subsequent treatment. The presence of various mineral salts 
will change the color from a red to a blue, or even green or 
gray, and it would be a useful and valuable work to systema- 
tize the action of these inorganic compounds, notably the chlo- 
rides of aluminum, tin, palladium and calcium, the acetate of 
lead, and the sulphates of copper and iron, on the several organic 
dyes in use by microscopists. 
CARMINE (CARMINIC ACID). 
This was the first staining medium to be employed in his- 
tological demonstrations and is still confessedly the most relia- 
ble. Bear in mind, it is not written that itis the best always be- 
cause in some cases it will not answer at all, but for general study 
it cannot be excelled for the ease with which it may be used 
and the certainty of its action. The bright red tint imparted to 
tissues by its action has been urged as an objection to its use, 
but it is the writer’s opinion that the red tinge is less trying to 
the eyes than the effort which must be made when the fine de- 
tails of a complicated structure have a less marked color. Be- 
sides it has so far proven itself the most durable of the many dyes, 
a specimen once stained with it may without fear be subjected to 
any treatmentin the embedding or mounting,or the object stained 
in mass may be kept in a preservative fluid until wanted for 
sections. It is probable that a study of carmine and a develop- 
ment of its capabilities would fit it for any work. 
BORAX—CARMINE. 
1. Make an aqueous solution of borax (4 per cent.) and 
carmine (2 or 3 per cent.), heating till both are dissolved. 
2. The above and 70 per cent. alcohol are mixed in equal 
parts and allowed to stand for two days and then filtered. 
By reason of its superior penetration, this solution stains 
more uniformly than any other with which I am acquainted, ex- 
cept perhaps, the one which follows. The specimens may be left 
in it from 10 to 30 minutes for small pieces and sections, to one 
or two days for large objects such as embryos, etc. When the 
staining is completed, the specimen should present a uniform 
dark wine color. It is now transferred to acid alcohol (see un- 
