The medicinal utility of the Leech seems, even in very remote times, to
have been acknowledged by mankind, and accordingly we find it noticed
in the writings of many ancient physicians. It was not simply applied
to the cases in which it is at present employed, but was recommended
to be used in many singular ways: a paste made of the ashes of a burnt
leech was said to have the property of removing the hair from any
part of the body. It was also employed to suck the blood from a wound
occasioned by a mad dog, or any other rabid animal.
At present the employment of this useful creature is confined to the
operation of drawing blood from inflamed parts of the surface of the
body, for which use it is eminently adapted.
There are as many as twelve or fifteen species of these creatures,
but only two have been employed in medicine, namely, the _Hirudo
medicinalis_, which may be known by having six yellowish lines, or
striæ, on its back, while the under part is of a grayish hue spotted
with black, but, as we shall presently see, these markings are not
uniformly found; and the _Hirudo troctina_, of a brownish colour,
the upper part of the body marked with black spots, each of which is
surrounded with a golden-coloured ring, the sides of a dingy yellow,
and the under part of a yellowish green with black spots.
The first of these species, the medicinal leech, is common throughout
the whole of Europe, but is much more abundant in the Southern parts;
it is generally about three inches in length. Formerly it was very
abundant in Great Britain, but the improvements in agriculture,
and the consequent drainage of the land, together with the great
use made of it in medicine, have of late years rendered it of less
frequent occurrence. On this account great quantities of leeches are
imported; these chiefly come from Bourdeaux and Lisbon. On a moderate
calculation, it appears that, in England, on an average, out of every
hundred leeches employed, ninety-nine may be considered of foreign
production; these differ from the English leech in being somewhat
larger, and having the under part of a uniform colour, without spots.
Some idea may be formed of the number of leeches used in medicine by
the statement, that in the hospitals of Paris alone, 300,000 were
employed in one year. The prevailing colour of the medicinal leech
appears to vary according to the nature of the soil on which it is
found. In Winter the leech retires to waters of considerable depth, and
seeks shelter in the mud at the bottom; but in the Summer it appears
to delight in shallow pools, basking, as it were, in the warmth of the
sun: but if the water it frequents is in danger of being dried up by
the Summer-heat, the leech buries itself in the mud at a considerable
depth. Just before a thunder-storm, leeches appear much agitated,
and rise frequently to the surface of the water; this, therefore, is
considered by the _leech-gatherers_ as a favourable time for collecting
them.
The property by which a leech anticipates thunder, has induced some
persons to employ it as a species of barometer; for this purpose a
leech is enclosed in a glass vessel half-filled with water, and the
following is supposed to be the result. When the weather is about to be
serene and pleasant, the leech will remain at the bottom of the vessel
without the least movement; secondly, if it is about to rain, the
animal will rise to the surface, and there remain until the approach of
fine weather; thirdly, before boisterous weather, it will appear in a
state of great agitation; fourthly, on the approach of thunder, it will
remain out of water for several days, appearing agitated and restless,
and so on.
This natural barometer _appears_ to answer tolerably well, if there is
sufficient belief in its virtues on the part of the possessor, and if
one leech only is employed; but when several of these creatures are
enclosed in the same vessel, they do not appear to obey the same laws,
and, consequently, their movements do not correspond with sufficient
accuracy to render their indications of the weather of much use.
The medicinal leech appears during its whole life to exist on the blood
or other juices of the creatures on whose body it fixes itself; this is
not the case with the horse-leech, which lives entirely on the _larvæ_
of aquatic insects, worms, &c., so that the common idea of the danger
of the bite of the horse-leech is without foundation.
The horse-leech is exceedingly voracious, not only swallowing worms,
tadpoles, &c., but even preying upon its own species. Sixty-five
horse-leeches were placed in a glass vessel, and in five days the
number was reduced to fifty-two, and not a vestige of those that were
missing was to be discovered.
The usual slowness of action of the digestive powers in all animals of
cold blood, was curiously illustrated in the case of a horse-leech,
which, after swallowing two small leeches of a different species,
disgorged one of the two at the end of three days, in a living state,
and apparently not much injured from its sojourn in so unusual a
lodging; but it enjoyed its liberty only for a few hours, its more
powerful companion swallowing it a second time at the end of that
period.
A number of this species of leech, inhabiting the water that supplied a
trough in which a tench had been placed, fixed themselves to different
parts of the body of the fish, and so effectually was the poor tench
annoyed, that it was soon deprived of life. “The leeches then tore it
(previously breaking the line of connexion between the various parts of
the body, by inflicting a vast number of bites or wounds,) into such
pieces as they could readily receive into the stomach, and so diligent
were they, that in a few days nothing remained of the fish but the mere
skeleton.”
From these habits it would appear, that the name of Hirudo
_sanguisuga_, (the blood-sucking leech,) has been improperly applied to
the horse-leech; on this account a recent author has suggested the name
of Hirudo _vorax_, (the voracious leech,) as being more suitable to its
nature.
Leeches are supposed to be very long-lived; two were preserved in
confinement for eight years before they died, and the well-ascertained
slowness of their growth seems to place their length of life beyond a
doubt.
On the head of the medicinal leech ten points are arranged in the form
of a horse-shoe, thus—
[Illustration]
These are considered, by some authors, to be organs of sight, or
eyes, while, on the other hand, it is stated by others, that they are
merely tubercles. Lamarck was of this opinion, and, consequently, in
describing their character, says they are without eyes.
The teeth, or rather piercers, with which the leech is furnished, are
three in number, of a hard gristly substance, and so placed, with
regard to each other, as to meet in the centre at equal angles; these
piercers are thrust into the skin when the animal attaches itself; not
by one plunging effort, but by constantly scratching or sawing upon the
surface (assisted at the same time by the sucking action of the lips);
in this manner they gradually become buried in the skin, and there
remain as long as the creature retains its hold; this movement of the
piercers occasions the gnawing pain felt for the first two or three
minutes after the leech has commenced operation.
Leeches are at times so scarce and valuable, that great care has been
taken in preserving them in a healthy state and fit for use. The
principal art in managing them consists in placing them in vessels
sufficiently large, keeping the water clear, and in removing those
which are unhealthy as soon as they are discovered.
Leeches, when applied to the skin, frequently show little inclination
to bite, and many plans have been resorted to, to induce them to
commence operations, such as bathing the part with milk, &c.; but
these methods may be considered useless, and the best plan appears
to be, to wash the part clean, and this is the more necessary when
any embrocation has been previously applied; but the surest way is to
puncture the place slightly, so as to cause the blood to appear. If the
little surgeon, before it is fully gorged, appears lazy and unwilling
to proceed, it can be usually roused by being sprinkled with a little
cold water.
After a leech has fallen off, it is usual to sprinkle salt on it to
induce it to disgorge the blood it has swallowed; but as the salt
frequently blisters its body, it has been recommended by Dr. Johnson of
Edinburgh, from whose work on the Leech, we have obtained most of the
preceding information, to apply a small portion of vinegar to the head
of the leech instead of salt.
The necessity for obliging the leech to dislodge the blood it has
swallowed, arises from the fact that it would remain in the body of
the animal for some months before it could be all digested; but the
most singular thing is, that, during the whole of this time, the blood
remains in nearly as fluid a state as when it was newly swallowed[5].
The stomach of this creature is very curiously formed, being composed
of a number of chambers, each chamber having a separate connexion with
the intestinal canal, in such a manner that, at the will of the animal,
the contents of each chamber can be emptied singly into that canal,
through a distinct opening.
[Illustration: Fig. 1. Fig. 2.]
It was long a matter of dispute as to whether leeches were produced
from eggs or born alive, but it is now ascertained that the ova are
developed in a singular case, having some resemblance to the cocoon
of a silkworm. The following engraving represents this case, of its
natural size: fig. 1, shows the perfect case or cocoon, and fig. 2, the
same opened, with the young leeches contained within it; it is said
that, at times, there are as many as thirteen or fourteen in one case.
This cocoon is formed by the parent animal, and by it deposited in the
mud or clay, which composes the bed of the pool it inhabits.
The fact of the young leech being produced from these cocoons, although
only latterly ascertained by naturalists, was long since well-known to
the dealers in leeches on the French coast, who avail themselves of
this knowledge of their habits, to multiply them for the purpose of
sale.
“It was by these means the leech-dealers of Bretagne, and particularly
in Finisterre, replenished the ponds in which they preserved those
leeches which were intended for the Paris market.
“About the month of April or May, according to the nature of the
season, they send out labourers, provided with spades and baskets, to
the little muddy marshes, where they are known to exist in abundance.
These workmen then set about removing those portions of mud that are
known to contain cocoons, which are afterwards deposited in sheets of
water previously prepared for their reception; here the young leeches
quit the cocoons, and are allowed to remain for six months, when they
are removed to larger ponds.” While they remain in these ponds, the
cattle and other animals are driven to the water, for the purpose of
allowing the young to feed upon them, as it is supposed that they grow
much more rapidly after having partaken of blood.
There is a small species of leech in the island of Ceylon, which is
more dreaded, and, from its great numbers, produces more evil, than
even the venomous reptiles which are found in the island, including the
terrible hooded snake itself.
The largest of these leeches are seldom more than half an inch in
length, and the smallest are minute indeed. This leech is a very active
animal; it moves with great rapidity, and is even said occasionally
to spring. It is supposed to have an acute sense of smelling, for no
sooner does a person stop where leeches abound, that they appear to
crowd eagerly to the spot from all quarters. In rainy weather, it is
shocking to see the legs of men on a long march thickly beset with
these creatures, gorged with blood, and the blood itself trickling down
in streams. It might be supposed there be little difficulty in keeping
them off; but they crowd to the attack, and fasten on more quickly
than they can be removed. Their bites are much more troublesome than
would be imagined, being very apt to fester and become sores, and, in
persons of a bad habit of body, to degenerate into extensive ulcers,
and ultimately cause the loss of a limb, if not that of life itself.
Many plans have, of course, been resorted to, to avoid this pest, such
as anointing the legs with tobacco-water, grease, &c., but all to very
little purpose, the only successful mode appearing to be, the enclosing
the lower part of the legs in boots and pantaloons, fitting very
closely to the limb, a very unpleasant dress in so sultry a climate.