PARASITES FREE DURING THEIR WHOLE LIFE.
This first category of parasites includes all those which are not
enclosed, and which live at the expense of others, without losing the
attributes and advantages of a wandering life; they are as free as the
vulture or the falcon which pursues its prey. We shall not, however,
include among them the parasitical kite of Daudin, which tears from
the hands of the traveller a piece of the flesh which he is preparing
in the open air, nor the small Egyptian plover, which keeps the teeth
of the crocodile clean. The former is a pirate, a highway robber; the
plover, on the contrary, is a kind neighbour, an attendant who
performs valuable services.
We are more correct in considering as parasites the Vampires
(_Phyllostoma_), those audacious bats of South America, which settle
on the sleeping traveller or his beasts, and suck their blood by means
of the sharp papillæ of their tongue. These animals are winged leeches
which bleed their victim and pass on. We place among free parasites
the greater part of leeches, some insects, and a certain number of
arachnida, crustaceans, and infusoria.
As we have mentioned free messmates, so we have free parasites, 108
which take advantage of their host, but with prudence and economy;
they ask from him nothing but his blood, and sometimes render him
important services. Many of these animals, both messmates and
parasites, have at present been only provisionally classified, and
cannot be definitely arranged till more observations have been made.
It is not always so easy as it may be thought to determine exactly the
relations which certain animals have with each other. We must pry very
narrowly before we can ascertain the motives which act on this
inferior order of beings. It is among free parasites that we find
those organisms which are generally called vermin, and which seem the
more capable of injuring their neighbours since they can the more
easily escape detection. These creatures, though they are called
vermin, excite no more repugnance in the mind of the naturalist than
the other works of creation; and St. Augustine did not exclude them
from his thoughts when he exclaimed, "_Magnus in magnis, maximus in
minimis_."
Leeches drink the blood of their victim, and when they are gorged to
the very lips, they fall off, taking a siesta for weeks or months.
Thus enjoying a repast at very long intervals, it is useless for them
to continue longer at table; and this is therefore another reason that
they should usually preserve their organs of locomotion, that they may
use them after their long period of digestion.
Like the annelids, they do not change their form, and as they are only
attached to their host for a short time, naturalists have not thought
fit to place them among parasitical worms, or Helmintha. However, if
we pass from the higher kind of leeches to those which live at the 109
expense of fishes, of crustaceans, and especially of molluscs, we see
that the desire of possessing a lodging is developed by insensible
degrees, and that the lower kinds, are by their form, their
organization, and their mode of life, as dependant as the greater part
of the helmintha. Thus we see Hirudinidæ on the Mya, an acephalous
mollusc, incapable of quitting their place, firmly fixed on the walls
of the stomach of their host, and living quietly at his expense. They
are called _Malacobdellæ_, and they have been so ill-treated by
Nature, that it is necessary to submit them to minute investigation in
order to determine their parentage.
The most well-known leeches are those which attack man and the other
mammalia, but some are also found on other vertebrate animals,
especially on fishes. Their organization is always proportioned to
that of the host which they frequent; thus, the simpler their host,
the lower is their organization. The mollusc harbours hirudinidæ much
lower in the scale than those which are found in fishes, and
especially in mammals.
Vampires make use of the papillæ of the tongue, and also of their
teeth, which act as so many lancets; leeches apply their toothed lip,
saw asunder the epidermis, and with the mouth applied to a network of
capillary vessels, suck till they fall off, intoxicated with blood.
We give here the different appearances which the skin assumes after
the bite of a leech. (Fig. 4.)
[Illustration: Fig. 4.--Different forms of the bite of a Leech.]
[Illustration: Fig. 5.--1. Sucker, open; _a._ jaws. 2. One of the
jaws magnified.]
[Illustration: Fig. 6.--Section of a Leech. _a._ anterior sucker; _b._
posterior sucker; _c._ anus; _d._ stomach; _æ._ æsophagus; _i._
intestine; _s._ glands of the skin.]
Fig. 5 (1 and 2) represents the jaws; 1, the jaws in their usual
position; 2, a single jaw, to show its outer edge, which is cut with
teeth like a saw.
Fig. 6 shows a leech with a section of its digestive tube. The 110
letters _d_ _d_ indicate the different cavities of the stomach, which
are filled in succession. We see in the fore part, the anterior sucker
with the mouth, and behind, the posterior sucker with the anus. At the 111
side of the stomach are seen traces of the glands of the skin.
We find a great variety in the mode of life of these hirudinidæ; and
if we sometimes meet with some which are sober and delicate, the
greater part show a voracity of which it is difficult to form any
idea. A leech has been met with in Senegal which draws a quantity of
blood equal to the weight of its body. There are leeches which devour
entire earth-worms. Fortunately the greater species are not the most
voracious: we might feel rather uneasy in the midst of leeches similar
to that which Blainville has described under the name of _Pontobdella
lævis_, which is not less than a foot and a half in length.
It is generally thought that all leeches are aquatic, but this is a
mistake. In the warm regions of the Old and New World, there live in
the midst of the brushwood, leeches which attack the traveller as well
as his horse, and suck the blood of both without their perceiving it.
Hoffmeister gives the following account with reference to small
leeches in the island of Ceylon:--
He had amused himself one evening by collecting some phosphorescent
insects which were hovering around him in considerable numbers; on
entering afterwards a lighted room, he perceived streaks of blood all
down his legs. This was the effect of the bites of leeches. These
creatures, said he, made a painful impression on me, the remembrance
of which was terrible. This same leech, which bears the name of
_Hirudo tagalla_, or _Ceylonica_, lives in the thickets and woods of
the Philippine Islands. There also it attacks horses as well as men.
It has also been noticed on the chain of the Himalayas, 11,000 feet 112
above the level of the sea. Japan and Chili also have terrestrial
leeches. The _Cylicobdella lumbricoides_ is a blind leech, which has
been found by F. Müller in damp earth, in Brazil.
The aquatic leeches are better known, and with but few exceptions, the
accidents produced by them are little to be feared. In Algeria it is
not uncommon, as army surgeons tell us, to see soldiers, while
drinking spring water, swallow small leeches which may do them injury.
We find from official reports that the French soldiers often suffered,
during the campaigns in Egypt and Algeria, from an aquatic leech
(_Hoemopis vorax_), which attacked the mouth and the nostrils, and did
not respect man any more than horses, camels, and oxen. The leech
discovered by Dr. Guyon under the eyelids and in the nasal fossæ of
the crab-eating heron of Martinique, is probably a monostomum, and not
one of the hirudinidæ. Leeches have also been found on turtles under
the name of _Eubranchella Branchiata_. Say saw one on a chelonian, and
others on tritons and frogs.
It is especially upon fish that these worms are found, and we cannot
hesitate to consider the greater part of them as true parasites. We
have described a whole series of them which live upon marine fishes,
especially on the barbel, the bass or sea-wolf, the halibut, the dab,
and different species of gadidæ. A. E. Verril published last year the
description of several kinds of American leeches, among which we see
two which infest a fish (_Fundulus pisculentus_) of West River, near
Newhaven. A large and beautiful species, which is known by the name of
_Pontobdella_, is also found upon the Rays.
A very skilful naturalist, Mons. Vaillant, has lately made these 113
animals the subject of study. Mr. Baird, in 1869, made known four new
Pontobdellæ, one from the coast of Africa, two from the straits of
Magellan, and one from Australia, found in one of the Rhinobatidæ. But
the most interesting in every point of view are the Branchellions,
which inhabit the electrical fishes known under the name of torpedoes,
and which do not fear to choose an electric battery as a place of
abode. These branchellions always attach themselves, as it appears, to
the lower surface of the body, and not to the gills as has been
thought; and they are distinguished from all their congeners by tufts
of filaments along their sides, which have been compared to lymphatic
branchiæ.
Many naturalists have considered these curious worms worthy of
attention, and have made many interesting observations upon them. One
of the finest memoirs on this subject is that of Mons. A. de
Quatrefages. We may here mention, in connection with their mode of
life, that neither Leydig nor Quatrefages found globules of blood in
their digestive cavity. The branchellions live on the mucous products
of the secretions of the skin, and instead of being parasites, we may
consider them as worms paying liberally for the room which they occupy
in their host, by maintaining his skin in good condition. They ought
rather to be classed among animals which render service to others;
that is, among mutualists.
In the fresh waters of Europe, a little leech-like animal, beautiful
both in form and colour, fixes itself on carps, tenches, and other
Cyprinidæ; this is the _Piscicola geometra_, which also lives on the
_Silurus glanis_. They are sometimes found in such great numbers that 114
they form around the gills a kind of living moss, which at last kills
the fish.
There are different leeches which inhabit invertebrate animals. Rang
mentions a little creature of this kind in Senegal, living as a
parasite upon the respiratory apparatus of an anodont. Gay discovered
in Chili one of the Hirudinidæ in the pulmonary sac of an Auricula,
and another on the branchiæ of a crab (_Branchiobdella Chilensis_).
Mons. Blanchard has noticed a malacobdella in the branchiæ of the
_Venus exoleta_; and it was known in the last century that the _Mya
truncata_ of our coast also lodges a malacobdella which lies always
under the foot of the animal. This is the hirudinean of which we have
spoken above, which is allied transitionally to the trematoda.
Together with the Hirudinidæ, we find very small worms, transparent,
bristling with daggers and spikes of every form, which are found
everywhere in fresh water. They are known by the name of _Naïs_. They
are so completely transparent that we can see the action of all their
organs through the substance of the skin. They have been the subject
of several remarkable works.
They live freely among the leaves of Lemna and other aquatic plants;
but there is one species much more restricted in their habitat than
the others; these seek assistance from the Lemneæ, and live at their
expense. It is because of this kind, of which the genus _Choetogaster_
has been formed, that we mention them here. Their long bristles are
veritable halberds, which they employ with astonishing skill, both in
attack and defence.
Among free parasites are found many very important articulated 115
animals, which neither the naturalist nor the physician ought to
ignore. Some of these increase with frightful rapidity on the skin
which harbours them, and their name alone is sufficient to inspire
disgust, if not horror: others live like leeches at the expense of
different animals, but without inhabiting them. There are many of
these which follow their host everywhere, and which are dreaded not
without just reason.
Of this kind are gnats, fleas, lice, bugs, and a great many others,
among which we ought not to forget the acaridæ, nor those singular
parasites of bats, which bear no slight resemblance to spiders
swimming in the midst of the fur. Volumes might be written concerning
the organization and the habits of these parasites. These small
creatures inspire the naturalist with no more disgust than the
earth-worm of our flower-beds, or the salamanders of marshy places.
Each one plays its part according to its conformation, and the most
abject in appearance is not always the least useful.
We will select among these parasites some two-winged insects, among
which there are many which suck blood. Those which are generally
called flies are divided into two groups, under the name of _Nemocera_
and _Brachycera_; many of these live only on blood, and are more
terrible than the lion and the tiger; in many countries man can defend
himself against those fierce carnivora, but he is there completely
powerless and without defence against these insects.
[Illustration: Fig. 7.--Antenna of a Gnat.]
Among the Nemocera are found the gnats (_Culex_ _pipiens_), those 116
brilliant children of the air, with fine and slender claws, and
delicate membranaceous wings, and wearing on their heads feathery
antennæ of rare elegance. They are known in the Old as well as in the
New World, and in southern regions it is necessary to guard against
their nightly attacks by musquito curtains. In the Antilles they bear
the name of _Maringouins_, and in hot countries they are generally
known as musquitoes. They are also called gnats, midges, black-flies,
zanzare, &c., in different localities, but as may be supposed, these
names do not always designate the same insect. The musquitoes of the
French colonies are often _Simulia_. At Madagascar and the Isle of
France is found the gnat known by the name of _Bigaye_.
In Davis's Straits, in lat. 72° N., Dr. Bessels, on board the
_Polaris_, was obliged to interrupt his observations on account of
these insects. A great number of them have been seen up to the 81st
degree of latitude. Besides gnats, there were also found _Chironomi_,
_Corethræ_, and _Trichoceræ_. As Dr. Bessels was able to save from the
_Polaris_ some small collections of insects, we shall soon know the
names of the species which live in these high latitudes. It is said
that the Esquimaux and the Lapps cover their skin with a coating of
grease, not only to lessen the effect of the cold, but to defend
themselves from the stings of gnats.
"The gnat is a plague from June till the first frosts," says Mons.
Thoulet, speaking of his abode among the Chippeways. "It renders the
country almost uninhabitable; and one is so exhausted by this
suffering, which does not cease by night or by day, and by the loss of
blood through their bites, that we manage to get through our daily 117
task only by the force of habit; we can neither speak nor think. When
the musquitoes disappear, the 'black-flies' come: the musquito pumps
up a drop of blood and flies away; the black-fly bites and makes a
wound which continues to bleed."
De Saussure has alluded to curious relations which exist in Mexico
between a bird, a beast, and an insect. "Bulls bury themselves in the
mud," says this learned traveller, "in order to avoid the attacks of
gnats, leaving in the air only the tip of their nostrils, on which a
beautiful bird, the Commander, posts himself, in this position the
Commander watches for the _Maringouin_ which is bold enough to enter
the nostrils of the animal."
Gnats are parasites in the same manner as leeches, since, like them,
they suck the blood, and live at the expense of others. There is,
however, this difference, that the females only are greedy of blood;
if this fail them, they live, like the males, on the juices of
flowers. Another difference is that they are completely harmless till
they have wings, and though they live long under their first form, in
damp earth or in water, the duration of their life as perfect insects
is of short duration.
We need not trouble ourselves about the active larvæ which swarm in
stagnant water, nor the chrysalids which float immovable in their
natural sepulchre. We give on the next page a representation of a
larva of the gnat. The females alone pierce the skin by means of an
auger with teeth at the end; they suck the blood, and before they fly
away, distil a liquid venom into the wound. This bite seems to have an
anæsthetic effect, which does not cause it to be felt till some time
after. The little spot around the wound appears as if affected by 118
chloroform.
[Illustration: Fig. 8.--Gnat (_culex pipiens_) larva and nymph.
(Blanchard).]
These parasites repay by an unkind action the assistance which they
have demanded from us.
Besides the gnats, which belong to the family of _Culicidæ_, there 119
there are also the _Ceratopogon_, and especially the _Simulium
molestum_, known in North America under the name of _Black-flies_:
"the tormenting black-flies of this country," as the Americans say.
Certain Nemocera, known by the name of _Rhagio_, put to flight both
man and animals.
They are very small; they get into the nostrils, and cause animals to
become blind by introducing themselves into their eyes. In addition to
these hurtful insects, we find others fatal to the life of animals,
and which are a real plague in certain countries.
The numerous travellers who have explored the interior of Africa, have
almost all spoken to us of a fly which attacks beasts of burden, and
kills them in a few hours; this is the Tsetse (_Glossina morsitans_).
More than one expedition has failed on account of this dipterous fly.
It was this which obliged Green to abandon his plan of reaching
Libebe, by causing him to lose one after another all his beasts of
burden and of draught. The horse, the ox, and the dog are more
especially attacked by this terrible fly between the 22nd and 28th
degree of longitude, and the 18th and 24th of south latitude. Happily
it does not produce any effect upon man.
There is another fly in Mexico which is dangerous to man; it is known
by the name of _Musca hominivora_, or more correctly, _Lucilia
hominivora_. Vercammer, a military surgeon of the Belgian army,
relates that a soldier in Mexico had his glottis destroyed, and the
sides and the roof of his mouth rendered ragged and torn, as if a
cutting punch had been driven into those organs. This soldier threw 120
up with his spittle more than two hundred larvæ of this fly. We give
below the figure of the larva and of the perfect insect. He had found
this man sick in Michoacan, at a height of 1,866 metres, between
Mexico and Morelia.
[Illustration: Fig. 9.--Lucilia hominivora.]
[Illustration: Fig. 10.--Lucilia hominivora, larva.]
My son-in-law, Dr. Vanlair, informs me that citric acid or the juice
of lemons is efficacious in destroying these insects. Injections of
this acid are thrown into the nasal fossæ.
At Brazil, in the province of Minas Geraes, they give the name of
_Berne_ to a fly which attacks man and cattle from the month of
November until February. It deposits its eggs in the loins, the arms,
the legs, or even the scrotum, without the victims perceiving it, and
their presence is first shown by a redness, then by a sensation of
itching, and a swelling with the formation of pus.
Among those insects which suck the blood, is one which is known by
every one, the Breeze-fly, _Tabanus bovinus_. Happily it seldom
attacks any animals except oxen and cows. We give a representation of
the insect, the parts of the mouth, and one of the antennæ.
In the same order of diptera are found ordinary flies, among which may
be easily distinguished the three species which are here represented, 121
and which differ as much by their external characters as by their mode
of life.
[Illustration: Fig. 11.--Ox-fly.]
[Illustration: Fig. 12.--Antenna of Ox-fly.]
[Illustration: Fig. 13.--Blue Fly.]
Another fly also attacks horses and cattle, and occasionally even man,
the _Asilus crabroniformis_, whose wounds sometimes draw blood.
Martins, the birds of the twilight, which fly in flocks above the
houses, describing circles and uttering shrill cries, are usually
infested by many vermin, among which we find a fly of considerable
size, which looks much like a spider, the _Ornithomya hirundinis_. It
moves about among the feathers with astonishing facility, and it 122
is not always confined to the same bird; it quits its host to
establish itself upon another, and sometimes throws itself upon man to
suck his blood.
[Illustration: Fig. 14.--Flesh Fly.]
[Illustration: Fig. 15.--House Fly.]
Some years ago these insects penetrated in the middle of the night
through the open windows into one of the apartments of the military
hospital at Louvain, and the next morning the skin of many of the
patients, and especially the bed-linen, were covered with stains of
blood. The physicians sent me some of these insects, not knowing
whence they had come, nor whether they had been the cause of this
annoyance. During the night, these Ornithomyæ had quitted their hosts
to attack the soldiers.
One of these insects, the banded Syrphus (_Syrphus balteatus_),
when in the larva state, seizes the rose aphides, and sucks their
blood with great eagerness.
But it is not precisely a case of parasitism, when the wounds of
soldiers are covered with larvæ, of which there were many sad
instances in the Crimean war. There are flies which deposit their eggs
in pus, as in all kinds of animal matter in a state of decomposition. 123
It is even said that these insects, deceived by the smell of the Arum
flower, will lay their eggs on the pistil. The name of _Myasis_ has
been given to the presence of these larvæ in a wound.
Every one knows that bats are often literally covered with vermin.
Among the many parasites which attack these little animals we find,
besides the acaridæ, a _Pteroptus_ of great agility, which seems,
as it were, to swim among the fur, and looks like a little spider or a
microscopic crab. There are but few bats on which we do not find some
of these, and we have sometimes seen them in such abundance, that it
was impossible to touch a single hair without disturbing them. This
species is usually called _Pteroptus vespertilionis_. It is
constantly in motion, and glides among the fur like a mole in a sandy
soil.
Together with these Pteropti lives a parasite of gigantic size, which
insinuates itself among the fur with equal dexterity, and bears the
name of _Nycteribia_. This has long claws like a spider, and plunges
deeply into the fur. These Nycteribiæ are found only on bats. They are
often associated on these animals with fleas and mites. Mr. Westwood
has written a monograph upon them. Mons. Plateau, our colleague, has
quite recently described a new species in the "Bulletins de l'Académie
de Belgique."
Among the insects justly dreaded by man, and which follow him
everywhere, is found one of the Hemiptera, known by every one under
the name of bed-bug (_Cimex lectularia_). It is said that this insect
was unknown in the capital of Great Britain before the fire of
London in 1666. According to some entomologists, it was introduced 124
into Europe in some wood that came from America. It is only necessary
to make this slight reference to the Cimices; their congeners are, for
the most part, parasites of plants, and live on their sap.
[Illustration: Fig. 16.--Bed-bug.]
To the same order belongs the singular hemipterous insect of our
ponds, the boat-fly (_Notonecta_). It has some feet suited for
swimming, and others for running, and it swims on its back with great
rapidity. It is a dangerous neighbour for everything that has life.
Always greedy of blood, it attacks great as well as little animals,
and sucks the blood of its victim to the last drop, so that it must be
closely watched when placed in an aquarium.
Lice, concerning which we are about to add a few words, are also free
parasites, and belong to a different order of insects. Their mouth is
formed of a sucker contained in a sheath, without articulations; it is
armed at the point with retractile hooks, within which are four
bristles. They have climbing feet, terminated by pincers, with which
they seize the hair of the animals on which they live; their eggs are
known by the name of _nits_. We have represented in Figs. 17, 18,
and 19, the complete insect, the head, the sucker, and a claw more
highly magnified.
Lice are hatched at the end of five or six days, and reproduce at the
end of eighteen days. Leeuwenhoek calculated that two females might
become the grandmothers of 10,000 lice in eight weeks. They are all
parasites of the mammalia, and three species live at the expense of 125
man: the louse of the head, of which Swammerdam gave a detailed
description in his work entitled "Biblia Naturæ"; the body-louse,
which lives on the bodies of filthy people, forms a distinct species;
the third species is the louse which occasions the disease called
pedicularis, or _Phthiriasis_. These insects were formerly much
more common than they are at the present day. In 1825 Dr. Sichel
published a monograph concerning them; and there appeared in the
"Gazette Médicale" of 1871, a long article on the history of
_Phthiriasis_.
[Illustration: Fig. 17.--Louse of the Head.]
It is stated that several great personages have fallen victims to its
attack, but these observations date from a period when it was thought
that they could be spontaneously originated. It is in fact difficult
to believe, as it has seriously been stated, that lice have been seen
to issue from the bodies of men like a spring of water from the earth.
A physician of the 16th century, named Amatus Lusitanus, speaks of a
great Portuguese nobleman who was so covered with lice that two of his
servants were constantly occupied in collecting them and carrying them
to the sea. Andrew Murray has published a memoir on the lice of the
various races of men.
The name of helminthiasis has been proposed for worm disease in
general, and either tæniaceous or lumbricoidian helminthiasis,
according to the species which made its appearance. These parasites
were considered to be formed spontaneously, and their presence 126
constituted a pathological condition, two errors which have now been
recognized, and by which the science of medicine has profited.
The _Phthirius pubis_ is another species which has been found only on
white races, and attaches itself especially to the hair on the pubis.
Mons. Grimm has published in the bulletins of the Academy of St.
Petersburg, an interesting memoir on the embryogeny of this insect;
and, more recently, Mons. L. Landois, of Griefswald, has completely
studied its habits.
[Illustration: Fig. 18.--Louse of the Head; 2, 3, sucker.]
[Illustration: Fig. 19.--Louse of the Head, claw.]
We are now about to refer to certain parasitical insects whose name is
usually associated with those which have preceded; they are well known
by all, and attack both men and the mammalia with no less ferocity; we
allude to fleas, which differ from gnats in this respect, that the
male is as eager for blood as the female, and that both of them, like
leeches, live by sucking it; besides, the larvæ of fleas live only on
what the full-grown insects bring them, whereas the larvæ of gnats 127
get their own living; the mother flea sucks for herself first, and
then divides the spoil with her larvæ which as yet have no feet. For a
long time it was thought that the fleas of different animals belonged
only to a single species, and consequently that the flea of man was
not different from that of a cat or a dog.
Daniel Scholten, of Amsterdam, in 1815, showed by his microscopical
observations, that fleas differ from each other; and in 1832, Dugès of
Montpellier, investigated the distinctive marks of the various
species. The observations of Scholten may be found in "Les Materiaux
pour une faune de la Néerlande," by R. T. Maitland.
The ordinary flea is called _Pulex irritans_, and especially attacks
man in Europe and in North America; it may be called a fly without
wings, and, together with its congeners, it forms a distinct family
under the name of _Pulicidæ_. Van Helmont treated of these insects,
and gave directions for making them, just as though he were describing
a recipe for pomade. At that time, naturalists supposed that certain
fish could be formed spontaneously, and that nothing but fermentation
was necessary in order to bring forth a crowd of living creatures from
this molecular disaggregation. Fleas may, perhaps, some day find a
place in the chemist's shop as well as leeches. We see no reason why
homoeopathic bleedings should not be resorted to, as well as
homoeopathic medicines; we should certainly have more confidence in
the effects of the bites of fleas, than in the efficacy of remedies
subdivided into the millionth part of a grain.
Fleas differ much in size, according to the places which they inhabit. 128
Dugès, of Montpellier, gives us a curious instance of this. He devoted
himself to researches on the zoological characters of this genus,
studying the four species which are the best known, the _Pulex
irritans_ of man, _Pulex canis_ of the dog, _Pulex musculus_ of the
mouse, and _Pulex vespertilionis_ of the bat.
[Illustration: 20.--Human Flea (_Pulex irritans_), after Blanchard.]
Fleas of a brown colour, almost black, and of enormous size, are
commonly met with on the sandy shores of the Mediterranean, at least,
in the neighbourhood of Cette and Montpellier; they are more than half
as large as a common fly. These are human fleas, and their presence on
the sea-shore during the heats of summer is due solely to the great
number of bathers of both sexes and of all classes, which lay their
clothes down there. If at some future day these insects were to be
placed in the rank of surgical species, it would be necessary to
resort to those shores in order to procure them; and we might suppose
that, by judicious crossing, we might soon produce races that would be
of real service; as yet, however, the therapeutic art has had 129
recourse only to leeches. Since we have seen these insects harnessed
and performing their exercises in public, we cannot say that the
future may not reserve for us a still greater surprise.
None who saw them can have forgotten the exhibition of learned fleas
made by a young lady who had sufficient patience to train them.
Walckenaer saw them in Paris, and examined them with the eye of an
entomologist; he relates that thirty fleas performed their feats at
evening exhibitions, for admission to which the sum of sixty centimes
was paid; that these fleas stood on their hind legs, armed with a
pike, which was a very thin splinter of wood; some dragged a golden
chariot, others a cannon with its carriage, and all were attached by a
golden chain on the thighs of their hind legs.
It is curious to see how Leeuwenhoek described, two centuries ago, the
history of the flea, with all its details, the accuracy of which can
scarcely be surpassed. He observed their entire anatomy, as far as was
possible with the instruments of his time (1694), and his descriptions
are accompanied by excellent plates; he saw them copulate and lay
eggs, and followed their whole development.
The finest fleas, both as to their size and form, inhabit the bats.
Fleas are often found on horses. A colonel of cavalry, on his return
from the frontier in 1871, sent me some of these insects, with the
request that I would examine them. He added that the horses of his
regiment were literally eaten up by them. It was the _Hematopinus
tenuirostris_. There is a species peculiar to monkeys, which Mons.
Paul Gervais has described under the generic name of _Pedicinus_.
At the commencement of the last century, a certain physician 130
attributed the cause of almost all diseases to microscopical insects,
and gave figures of ninety species which were supposed to produce, in
some cases smallpox, in others rheumatism and gout, jaundice and
whitlows. Almost all these figures represent imaginary creatures. This
opinion has reappeared in modern times; how many persons have been
seen to smoke camphor in order to preserve themselves from the
invasion of animalcules. I do not speak of the apparatus which has
been contrived in order to breathe nothing but air which has been
filtered and deprived of its living germs.
There are some of the articulata with four pairs of feet, a kind of
microscopic spiders which require to be noticed here; these are the
numerous Acari which infest many animals. Some of these wander on the
surface of the skin, others in galleries under the epidermis, and many
pass from one animal to another without changing their form or mode of
life. There is a considerable number of them; no class of the animal
kingdom is free from them, neither aquatic nor terrestrial animals,
neither vertebrates nor invertebrates. These parasites belong for the
most part to the same family, and cause by their presence a disease
which was for a long time considered to be peculiar to the skin.
An English naturalist, Mr. George Johnson, carefully studied the
parasitical and free acaridæ of Berwickshire. Mons. Ehlers has written
a very interesting work, with fine illustrations, on the acaridæ of
birds, published in the "Archives of Troschel." There is more than one
species which lives at the expense of man, and one of them produces 131
a disease known in every country and at all times under the name of
the itch; until 1830 its true nature was still unknown. It is not an
affection of the skin, as was thought, but merely the result of the
presence of these animalcules. The director of the special Hospital
for Skin Diseases at Paris was so fully convinced that the acaridæ are
not the cause of the itch, that he offered a prize to any one who
could render these insects visible. A student of medicine, a Corsican 132
by birth, had happened to see these itch-insects sought for in his own
country, and was the first to prove, in 1834, the real cause of the
disease. A resident student had given, in a thesis which he sustained
at Paris before the faculty of medicine, a drawing of a cheese-mite
instead of the itch-insect, and this error had caused it to be
supposed that the species peculiar to this disease did not exist. We
give in Figures 21, 22, 23, representations of the male and female
insect, greatly magnified.[2] Of course, all the treatment necessary
for the cure consists in getting rid of the animalcules and their
eggs, and in cleansing the skin and the clothes of the patient.
Petroleum oil has been judiciously prescribed in order to destroy the
mite, but the remedy which seems the most efficacious is Balsam of
Peru.
[Illustration: Fig. 21.--Sarcoptes scabiei, or male acarus of the
itch; the lower surface.]
[Illustration: Fig. 22.--Sarcoptes scabiei, female; the upper
surface.]
[Illustration: Fig. 23.--Sarcoptes scabiei, male; the dorsal surface.]
Most mammals have their peculiar species of acari, and the horse has 133
two which give rise to different skin affections. Since the presence
of these animals constitutes the disorder, it may be easily caught;
man may communicate it to domestic animals, and they may give it to
him. The itch-insect of man bears the name of _Sarcoptes scabiei_, and
no other species than those of Sarcoptes can be transferred from
animals to man. These animalcules have at different times been
diligently studied by many naturalists, and Dr. Füestenberg has lately
published a folio volume, under the title of "Die Krätzmilben der
Menschen und Thiere," with large lithographic plates, and
illustrations in the text. It is possible that the pustular disease
which prevails at Sierra Leone is originated by some peculiar acarus.
Another acarus parasitical on man, the _Persian Argas_, is fortunately
unknown in Europe. It is said to be common at Miona, and prefers to
attack strangers. Its stings produce acute pain, and travellers assure
us that they may be the cause of death. This acarus remains but a
short time on the person, and generally makes its appearance during
the night. It is called also the Miona bug. Fischer of Waldheim has
published a very interesting memoir on this parasite. Justin Goudot
has also observed another Argas (_A. Chinche_) which torments man in
the temperate regions of Columbia.
These Arachnida, for they are articulata with four pairs of legs,
often make their appearance where we should not expect to find a
living organism, and naturalists, under these circumstances, have,
with the best faith possible, supposed that they had seen these mites
produced spontaneously without parents. We have seen a remarkable 134
instance of this in the _Acarus marginatus_ of Hermann. On the 18th
Thermidor, an 2, they were making a _post mortem_ examination at
Strasburg of a man who had died of fracture of the skull, and when
opening the dura mater, they saw on the corpus callosum, a mite
running about which became the type of the species. The appearance of
this acarus under such conditions made, as may be supposed, much noise
at the time, but we should not be surprised if it had been introduced
during the operation by a fly seeking to lay its eggs.
In this group is found another interesting acarus, which is developed
in man in the sebaceous crypts of the nostrils. The name of Simonea
has been given to it, from Dr. Simon of Berlin, who made it his
especial study. This genus leads us by its form to the _Linguatulæ_,
the structure of which has been so long doubtful. The _Simonea
folliculorum_ belongs to the family of the _Demodicidæ_.
The dog harbours a demodex (_D. Caninus_) which causes it to lose its
hair. Some years ago, the sheep in Belgium were attacked by one of the
acaridæ, the _Ixodes reduvius_, which had been introduced from a
neighbouring country, and had multiplied with frightful rapidity.
Packard has given an account of an _Ixodes bovis_ on the _Erethizon
epixanthus_, and on the _Lepus Bairdii_, and an _Argas Americana_ on
cattle coming from Texas; this was published in the sixth report of
the United States' Geological survey (1873).
According to the observations of Mons. Megnin, the _Tyroglyphi_, the
_Hypopi_, the _Homopi_, and the _Trichodactyli_, are transitory forms
which ought not to be preserved as generic divisions among the acaridæ.
We have found on the small bat (_Pipistrella_) an acaride (_Caris 135
elliptica_) and a new _Ixodes_ which we have described in a special
memoir on the parasites of the _Cheiroptera_. Mr. Lucas caught an
ixodes on a dog, and kept it alive long enough distinctly to see it
lay eggs which proceeded from an oviduct. These eggs formed masses
attached to the abdomen of the mother.
An acarus (_Dermanyssus avium_) is found on birds, and multiplies with
such rapidity that it completely exhausts those on which it has
established itself. It has been seen accidentally on man. An instance
is recorded of a woman who could not get rid of these parasites,
because she passed every day through her henhouse in order to get to
her cellar, and the frightened fowls threw down upon her a perfect
shower of acaridæ. Not long ago mention was made at the Academy of
Medicine at Paris, of a sarcoptes (_S. mutans_), which produces a
disease among fowls, especially on the cock and hen, and which passes
from these to the horse and other domestic animals. This sarcoptes
prefers to live under the epidermis of the feet. Reptiles are not free
from its attacks, for it is often seen on lizards and serpents. We
have found a very curious one on the skin of a gecko from the south of
France.
Many insects are always covered with certain species of acaridæ. Every
entomologist knows that the body of the "watchman" beetle always has
some of these, like little living pearls, which wander especially on
the under side of the abdomen. It is the same with a small
coleopterous insect that is found abundantly wherever there is any
decomposing matter. Léon Dufour gave himself up to the study of some
of the parasites of insects, and mentions, among others, a species 136
belonging to the muscidæ, the _Limosina lugubris_, which does not
measure a line in length, and which harbours as many as fifteen
pteropti under its abdomen.
[Illustration: Fig. 24.--Hydrachna geographica.]
Bees, which give us their wax and their honey in exchange for the
shelter which we afford them, have a mortal enemy, an acarus, which
attaches itself to them, not in order to gain any advantage from them,
but to cause their death. It is not so much a parasite as an assassin,
and we may be excused from describing it. We have found acaridæ on
certain polyps, the _Campanulariæ_ and _Sertulariæ_ of our coasts, and
some years ago we described one which is very curious, and inhabits
the southern whale, in the midst of its Cyami and Tubicinellæ. The
anodonts of our ponds, as well as the _Uniones_ usually have the skin
of their feet and that of their mantle encrusted with acari of every
age, to which the name of _Atax ypsilophora_ has been given. The
species which live on the anodonts are not the same as those which
inhabit the _Uniones_; and Mons. E. Bessels, who has so fortunately
returned from his voyage to the North Pole, on board the _Polaris_, 137
has seen the species of the anodonts crossed with those of the Uniones.
[Illustration: Fig. 25.--Cheyletus eruditus.]
There are also Arachnida which are parasitical only while young, as
the _Trombidions_ and certain _Hydrachnæ_ (Fig. 24) which frequent
aquatic animals. The _Leptus autumnalis_, known in France, at least in
some localities, by the name of _Rouget_, is an acarian which throws
itself upon man, and especially attaches itself to the roots of the
hair: fortunately, it is only found in the country districts. The
_Acarus_ (_Cheyletus_) _eruditus_ (Fig. 25) lives in books and
collections, as well as on fruits and all kinds of bodies more or less
damp, left in dark places; it has been studied by Van Der Hoeven.
Mons. Leroy de Méricourt found in pus, which was running from the ear
of a sailor, acaridæ which Mons. Robin refers to the genus
_Cheyletus_, rather than to that of the _Acaropses_.
[2] Hardy, in his _Leçons sur les maladies de la peau_
(Paris 1863), devotes a special chapter to parasitical diseases,
and gives the complete history of the itch-mite.