74 NATURAL HISTORY OF BRITISH FRESH-WATER LEECHES.
that in 1849 they were still found in pools and wells in the
vicinity of the same lake. He also mentions that in summer the
leech-gatherers sat with their legs in the water and the leeches
fastened on them.
The supply of leeches in France at one time ran so low that
Algerian leeches (Hirudo troctina) were imported. Their use
was at first forbidden, but careful and extensive experiments
showed that no harm followed their application. These Al-
gerian leeches have a number of red spots, and a faint similarity
to the uniform of the French dragoon suggested the name of
"le dragon d'Alger." They were also used in England, where
they were called "Trout-leeches."
Mr. E. M. Holmes, F.L.S., tells me that only one firm in
London now imports leeches regularly. They are used in
infirmaries and hospitals and in physiological laboratories,
where the secretion "hirudin" is extracted and used to prevent
the clotting of blood in various experiments. A medical friend
informs me that they are still used in the East of London by the
alien population in cases of neuralgia, gumboils, etc. The non-
alien population sometimes use them for curing "black eyes."
Methods of capture and preservation of specimens.—
Leeches should be sought amongst aquatic plants growing in
ponds and streams and under submerged twigs and stones.
It is best to bring them home alive, and they may be easily
carried in corked tubes or bottles with a little water. Mr.
Harding writes me that a good plan for obtaining the small
species is to place quantities of weed in large aquaria. After
two or three days the leeches crawl to the sides and may be
picked off. Identification should be attempted before killing
the specimens. The small species may be narcotised with
soda water from a siphon, and if they are not kept too long
in the carbonated water they will revive on being transferred
to fresh water. For the larger species, the writer found that by
carefully adding methylated spirit to the water they are in,
the animals become narcotised. Mr. Harding advises immersion
in water at about 120o F. For the preservation of colour
and markings a 5% solution of formalin is best. Specimens
required for histological work need different treatment. Castle
(11) recommends the following method :—"Stupefy in soda-