134 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
ing a sufficient amount of carbonate of lime and other substances in 
solution to give a cloudy precipitate, after a time, which may effectually 
destroy the appearance of a specimen. 
Furthermore, delicate organisms should first be placed in weak 
alcohol (35 to 50 per cent.) for from two to six hours, the changing of 
the fluids being effected by a siphon, a small quantity of the weak 
alcohol being withdrawn and stronger added, until finally the desired 
strength is obtained. With delicate gelatinous structures the increase 
in the strength of the alcohol should be as gradual as possible. In 
many cases it is necessary to use a hardening or fixing reagent before 
the final consignment to alcohol, which is principally useful as a pre- 
servative. The most fixing reagents, according to Lo Bianco, are the 
following : — 
Chromic acid. — 1 per cent, in fresh water. Objects should not 
remain in the fluid longer than is necessary to fix them, as they are 
apt to become brittle. Subsequently they should be well washed with 
distilled water to prevent the formation of a precipitate when placed in 
alcohol, and also to prevent their taking on too green a tinge from the 
reduction of the acid. 
Acetic acid, concentrated, kills rapidly contractile animals, but 
must be used with caution, as it produces a softening of the tissues if they 
are subjected for too long a time to its action. 
Osmic acid, 1 per cent, solution, hardens gelatinous forms well, 
and preserves their transparency, but its prolonged action renders the 
objects brittle and gives a dark brown tint. Objects hardened in it 
should be well washed in distillled water before being placed in alcohol. 
Lactic acid. — 1 part to 1000 parts sea -water fixes larvae and 
gelatinous forms well. 
Corrosive sublimate. — Saturated solution in fresh or sea-water; may 
be used either hot or cold. It acts quickly, and preserves admirably 
for histological purposes. It is especially good combined with copper 
sulphate, acetic acid, or chromic acid. Objects hardened in it should be 
subsequently well washed in distilled water and in iodized alcohol (the 
recipe for which is given below), to remove all traces of the sublimate, 
which in alcohol crystallizes out in the tissues of the organisms and so 
injures the preparation. 
Bichromate of potassium. — 5 per cent, solution in distilled water 
hardens gelatinous organisms slowly, without rendering them fragile. 
It gives, however, a precipitate in alcohol, and discolours the specimen. 
The discoloration, however, may be removed by adding to the alcohol 
a few drops of concentrated sulphuric acid. 
Copper sulphate. — 5 per cent, or 10 per cent, solution in distilled 
water, used either alone or in combination with corrosive sublimate, 
kills larvae and delicate animals without distortion. The objects should 
be subsequently repeatedly washed with water to remove all traces of 
the salt, otherwise crystals will form when the object is placed in 
alcohol. 
Various combinations of these reagents are especially useful, and 
some of those most serviceable are given here : — 
Alcohol and chromic acid. — 70 per cent, alcohol, 1 per cent, chromic 
acid, equal parts. 
