FLIES
PART I
THE HOUSE-FLY (_Musca domestica_)
Musca est meus pater, nil potest clam illum haberi;
Nec sacrum nec tam profanum quidquam est, quin Ibi ilico adsit.
(PLAUTUS, _Mercator_.)
‘THE common house-fly [says Ruskin] is the most perfectly free and
republican of creatures. There is no courtesy in him; he does not
care whether it is a king or clown whom he teases, and in every step
of his swift mechanical march and in every pause of his resolute
observation there is one and the same perfect expression of perfect
egotism, perfect independence and self-confidence and conviction
of the world having been made for flies. Your fly free in the air,
free in the chamber, a black incarnation of caprice, wandering,
investigating, fleeting, flitting, feasting at his will with rich
variety of feast from the heaped sweets in the grocer’s window to
those of the butcher’s back yard, and from the galled place on your
horse’s neck to the brown spot on the road from which, as the hoof
disturbs him, he rises with angry republican buzz; what freedom is
like his?’
The house-fly is all that Ruskin describes it to be, but it is more. It
is the most cosmopolitan of insects. Wherever man is there is the fly.
It is found—
From Greenland’s icy mountains
To India’s coral strand.
But it is naturally more frequent in warm climates than in cold, as
the rate of its development depends very largely upon an average high
temperature.
Unlike the lice and the bed-bug, the fly like the flea, passes through
a complete metamorphosis—egg, larva, pupa, and imago. It will breed
in almost any rotten matter, whether vegetable or animal, and it
breeds most successfully, as Gordon Hewitt has pointed out, when
certain processes of organic fermentation are taking place in its
breeding-place. Probably the fermentation has a favourable effect upon
the food of the larvae. Undoubtedly the place most readily selected by
the female for laying her eggs is stable-manure. A few years ago there
was a remarkable reduction in the number of house-flies in London, and
Lord Montagu of Beaulieu attributed this reduction to the refreshing
and insecticidal petrol vapour with which the streets of that town
were then bathed.
[Illustration: FIG. 14.—Mass of eggs of _M. domestica_. (From Gordon
Hewitt.)]
I do not know what experiments Lord Montagu had made on the subject
of the insecticidal value of petrol vapour, but the ordinary man in
the street attributed—and I think more correctly—the diminution of
the plague of flies to the absence of the nidus in which the female
fly lays her eggs. Stable-yards had been turned into garages. But
flies will, indeed, breed in almost any kind of dejecta—including the
human—and in rotten straw, rotten wool, cotton garments, decaying
vegetables and fruits, bad meat, rotten grain, and even in spittoons,
but they prefer horse-manure.
[Illustration: FIG. 15.—Eggs of _M. domestica_, × 40. (From Gordon
Hewitt).]
In our country house-flies usually begin to breed in June and July,
continuing well on into October if the weather be but warm. Their
greatest activity is, however, in the hotter month of August and the
beginning of September. But in warm stables, restaurants, and kitchens
flies are able to reproduce the whole year round. A single fly will
deposit at one time 100 to 150 eggs, and in the course of her summer
life may produce five, or even six, batches of ova of this size. The
eggs are pearly white, elongated structures, with two converging lines,
along which the egg-case will ultimately split to give exit to the
larva. The eggs are laid, by means of a long ovipositor, a little way
beneath the surface of the dung-heap in a position where they will not
readily be dried up. In favourable conditions the eggs hatch in from
eight to twenty-four hours.
The first larva is legless, tapering towards the head, which bears
a pair of breathing-holes, or spiracles; the body is much stouter
towards the hinder end. On the whole it is a white, unpleasant-looking
maggot, called by freshwater-fishermen a ‘gentle.’ By contracting and
expanding its body it pushes its way through the moist, semi-liquid
surroundings. The skin is usually moulted some twenty-four hours after
birth, but all these time-limits depend much upon the temperature and
favourable conditions. With normally high temperatures—say, with 30° C.
to 35° C.—the larva will become fully grown in five or six days. The
third and final larval stage, after the second moult or ecdysis, lasts
three days, and when fully grown the maggot is now about half an inch
in length. Externally, twelve segments are visible, but the internal
anatomy shows that thirteen are really present, though one is almost
‘masked.’
[Illustration: FIG. 16.—Abdomen of female house-fly, showing the
extended ovipositor. (From Gordon Hewitt.)]
It is only during these larval stages that the insect grows, and it
is never more bulky than in the third larval stage. Now it leaves the
moist situation, in which it has flourished, and, crawling through the
manure, seeks some dry or sheltered corner. For a time it rests, and
then after an hour or two’s quiescence it retracts its anterior end
and assumes a barrel-shaped outline, its creamy white colour slowly
changing to a mahogany brown. The larval skin forms the pupa-case,
and within this pupa-case the body of the larva undergoes a wonderful
change, far greater than even human beings undergo at the time of
puberty. Many of its organs are disintegrated and re-formed, and in the
course of three or four days the white, legless, repellent maggot, who
‘loves darkness rather than light,’ is changed into a lively, flying
insect, seeking ‘a place in the sun’ and the companionship of man. As
the Frenchman said of the pig which goes into one end of the machine in
the Chicago meat-factory as live pig and comes out at the other end in
the form of sausages, ‘Il est diablement changé en route.’
[Illustration: FIG. 17.—Mature larva of _M. domestica_. _a.sp_,
Anterior spiracular process; _an.l_, anal lobe; _sp_, spiniferous pad.
I-XIII, Body segments. (From Gordon Hewitt.)]
In a very short time after leaving the pupa-case the adult fly has
stretched her wings, the chitin of her body has hardened, and she flies
away ‘on her several occasions.’
[Illustration: FIG. 18.—‘Nymph’ of _M. domestica_ dissected out of
pupal-case about thirty hours after pupation. _an_, Swellings of
nymphal sheath marking bases of antennae; _cx_, coxa of leg; _lb_,
labial portion of proboscis sheath; _lbr_, labral portion of same;
_n.sp_, spiracular process of nymph; _w_, wing in nymphal alar sheath.
(From Gordon Hewitt.)]
[Illustration: FIG. 19.—Pupal-case or puparium of _M. domestica_ from
which the imago has emerged, thus lifting off the anterior end or ‘cap’
of the pupa; ventro-lateral aspect. _a.sp_, Remains of the anterior
spiracular process of larva; _l.tr_, remains of the larval lateral
tracheal trunk; _n.sp_, temporary spiracular process of nymph; _p.sp_,
remains of the posterior spiracles of larva. (From Gordon Hewitt.)]
Flies become sexually mature in a week or ten days after emerging from
the chrysalis-case, and are capable of depositing their eggs four days
after mating, so that if the conditions be indeed favourable the whole
development from the egg to the perfect fly may be accomplished in nine
or ten days, and the second generations are able to lay their eggs ten
days later. The appalling fecundity of such an insect explains the fact
that in the hotter parts of the world nearly every edible thing seems
to be covered with them.
The proboscis of a fly can only suck up liquid food; and when we see
it feeding on solid substances, such as sugar, it has really dissolved
the sugar by depositing some saliva on it, and is sucking up the sugary
solution so produced. It not infrequently regurgitates its food in a
spherical drop, which it generally re-absorbs.
As we have seen, flies are very susceptible to temperature, and with
the approach of cold weather they seem to die. We used to think that
some, in a state suspended animation, ‘carried on’ through the winter
months. This is, however, ‘non-proven.’ Many of them undoubtedly die
in the autumn, as bees die, of old age. They are literally worn out.
But a great number fall victims to a parasitic fungus called _Empusa_.
Flies killed by this fungus are frequently to be seen in autumn,
hanging dead on windows, &c., surrounded by a little whitish powdery
ring of spores formed by the fungus.
Flies, like many other insects, are extremely difficult to keep alive
in captivity, and few have succeeded in rearing them for more than a
month or two. At one time, as we have said, it was thought that those
flies which survive the winter were fertilised females of the younger
broods, and that during the winter they subsisted on their ‘fat bodies.’
[Illustration: FIG. 20.—_M. domestica_ in the act of regurgitating
food. × 4½. (From Gordon Hewitt.)]
Doubt has recently been thrown on this theory, and in a recent
report[8] of the Local Government Board Dr. Newsholme sets forth the
results of the researches of Dr. Monckton Copeman and Mr. E. E. Austen
in the following words:—
Until recently there was general agreement that a certain number of
flies managed to survive the winter and spring by hibernating in
dark nooks and crannies in dwelling-houses, or, as contended by Dr.
Laver,[9] in various sheltered situations outside dwellings—such as
the under-surface of the thatch of farmyard stacks. The researches of
Mr. Jepson and others have shown that, during the period extending
from late autumn to early summer, flies may be found occasionally
in all active conditions in warmed houses, and especially in such
places as kitchens and bake-houses, where the temperature is kept
relatively high; and further, that under these conditions, and in
presence of sufficient food material they may even continue to breed.
Doubt has, however, been expressed as to whether a sufficient number
of flies remain in active condition in these localities to perpetuate
the species and to start the rapidly multiplying generations of the
following summer. As to whether flies can persist through the winter
in other than adult form practically nothing is known.
In view of the importance of obtaining further information on these
points, some inquiries were undertaken into the hibernation of flies,
the results of which were set out in a communication by Dr. Copeman
published in the sixth report of this series. Arrangements were made
with a working naturalist for the collection of any flies that could
be found in situations like those which Dr. Laver and other observers
had found to be favourite winter quarters of hibernating flies. In
view of the need, pointed out by Howard, for expert identification of
the species of all flies captured in a dormant condition during the
winter months, the co-operation of Mr. Austen of the British Museum
(Natural History) was obtained, and to him all the flies collected
were submitted for examination. The one specially interesting and
unexpected point emerging from this inquiry was that not a single
specimen of the house-fly (_Musca domestica_) was met with among the
considerable number of hibernating flies caught in situations which
have hitherto been regarded as the special habit of this fly. Under
these circumstances it was felt that further detailed investigation
of the matter was needed; and, accordingly, inquiry on a more
extended scale, and covering—as it proved—an extensive area, was
initiated and carried through during the past winter.
* * * * *
Once more, the results obtained afford no support to the belief that
house-flies hibernate, in this country, in the adult state; and the
problem as to the manner in which the interval between one fly-season
and the next is bridged over still remains unsolved.
Gordon Hewitt, Copeman, Howlett, Merriman,[10] and others, have made
experiments as to how far a fly can travel. Marked flies have been
taken within forty-eight hours at distances ranging from 300 yards to a
mile. Apparently the direction of the wind plays a considerable part
in the distance they travel.
The importance of the house-fly as a carrier of disease, especially
bacterial disease, has recently been recognised especially in times of
war. Moses was as great as a Principal Medical Officer as he was as a
Director of Supplies; and this is shown in Deuteronomy, chapter xxiii,
where he deals with the need of strict hygiene in the camp.
In the middle of the last century already attention was being drawn
to the fact that the house-fly and the blow-fly transmitted various
diseases. But it was during the Spanish-American War and the South
African War which followed shortly afterwards that the part played by
these pests in conveying enteric became definitely established. Flies
coming straight from the latrines, with their legs and their wings and
their proboscides soiled with typhoid bacilli, would enter the camp and
the tents of the soldiers and settle on their food-supplies—crawling
over their jam, floating in their milk. Thirty per cent. of the deaths
in our South African War were due to typhoid fever. The bacillus, as is
well known, is capable of existing for a long time and of persisting
alive in the alimentary canal of the insect. Dr. Graham-Smith has shown
that the bacilli may remain active for six days after feeding, and
that the feet of flies which have the bacillus on them are capable of
infecting surfaces upon which they walk for at least two days after
first coming in contact with the germs that cause ‘enteric.’
[Illustration: FIG. 21.—A, Foot of a fly, showing hairs bearing
bacteria; B, a single hair more highly magnified; C and C´, bacteria.
Diagrammatic.]
Faichne reared maggots in dejecta infected with typhoid bacilli, and
he was able to show that the flies into which these maggots turned
contained virulent typhoid germs in their intestines. There is
absolutely no doubt that typhoid is largely conveyed by the agency of
these insects; and as flies are perfectly controllable, if ‘the people
will but have it so,’ it is one of the disgraces of our civilisation
that this disease should be so prevalent.
The protective inoculation against enteric is now almost perfect, and
its value is shown by quotations from a leaflet issued by the Research
Defence Society:—
Sir William Leishman, in a letter published during the present war,
August 22, 1914, says: ‘The benefits of inoculation are so well
recognised in the regular forces that we find little difficulty,
in foreign stations, in securing volunteers for inoculation: for
instance, about 93 per cent. of the British garrison of India have
been protected by inoculation; and typhoid fever, which used to cost
us from 300 to 600 deaths annually, was last year responsible for
less than 20 deaths. Inoculation was made compulsory in the American
army in 1911, and has practically abolished the disease; in 1913
there were only 3 cases, and no deaths in the entire army of over
90,000 men.’
In Avignon, in the south of France, during the summer of 1912,
typhoid fever broke out in the barracks. Of 2053 men, 1366 were
protected and 687 were not. The non-protected had 155 cases of
typhoid, of whom 21 died; the protected had not one case. In the
winter of 1913 the French Senate resolved that the protective
treatment should be made compulsory throughout the French army; and,
in special circumstances, among the reservists.
[Illustration: FIG. 22.—Chart illustrating the relation of the
numerical abundance of house-flies to summer diarrhoea in the city of
Manchester in 1904. Prepared from statistics and chart given by Niven.
(From Gordon Hewitt.)]
Infantile diarrhoea, which so afflicts the crowded, poorer quarters
of our cities in the summer, is another disease intimately associated
with _Musca domestica_. But that is hardly a disease likely to trouble
the soldiers. The tubercle bacillus is another germ conveyed by
flies. House-flies are particularly fond of feeding on saliva; and
Hayward, Lord, and Graham-Smith have obtained virulent bacilli from the
intestines and dejecta of flies which had been fed on tubes containing
tuberculous sputum. These experiments have been amply confirmed by
other workers. Anyone who has ever been in Egypt will remember the
terrible sight of the flies attacking little children suffering from
ophthalmia and it is believed that the wide prevalence of this most
pitiful trouble is attributable to the abundance of flies—the flies of
Egypt, a plague even in the times of the Pharaohs. Things do not alter
much in Egypt, and the Biblical plagues are wont to recur.
Another disease—anthrax, or wool-sorter’s disease—may be conveyed by
the same carriers from infected cattle to man, and there is a good deal
of epidemiological and bacteriological evidence available to show that
flies play an important part in the spread of cholera, which is now
threatening the soldiers in the eastern seat of the war, and possibly
in disseminating the organisms which cause yaws and tropical sore.
It will be noticed that the fly is not a necessary second host for any
of these germs. They are conveyed, as if by an inoculating needle, by
contact with the proboscis or the legs or some other tainted organ
of the fly. The bacilli, however, pass through the alimentary canal
apparently unchanged and unharmed, and are deposited either with the
regurgitated food from the fly’s stomach (Fig. 20), or with the dejecta
of the insect. There is no subcutaneous inoculation—such as takes
place in the case of the mosquito when it conveys malaria, or in the
case of the tsetse-fly when it conveys sleeping sickness—where the
disease-causing organism is injected into the human body. The action of
the fly is mechanical, but none the less efficient. The poisoning of
the soldiers’ food-supply is its chief rôle in war.
CHAPTER VI
FLIES
PART II
THE BLUE-BOTTLE (_Calliphora erythrocephala_),
AND OTHERS
Who fills our butchers’ shops with large blue flies?
(_Rejected Addresses._)
BUT there are other flies: first amongst which may be mentioned _Fannia
canicularis_ and _F. scalaris_. These belong to the family known as
Anthomyidae, and are distinguished from the house-fly by being smaller
in size, and by many other small details in the imago stage hardly to
be appreciated except by trained dipterologists. For a short time at
the beginning of the summer, during part of May and June, specimens
of _F. canicularis_ are more abundant than _M. domestica_, and, when
seen on the window-panes of our living-rooms, are apt to be thought, by
the uninformed, to be young specimens of the latter. But, as has been
said, flies, when they are once flies, do not grow; all the growing
they do is done in the larval stage.
[Illustration: FIG. 23.—Latrine-fly, _Fannia scalaris_, male (× 3).
Antenna. Head of female, dorsal view. Natural size, resting position.
(From Graham-Smith.)]
As the days lengthen the common house-fly becomes vastly more common
than _F. canicularis_, the ‘lesser house-fly,’ and the latter now tend
to aggregate in those rooms of our houses not devoted to cooking,
and may frequently be noticed flying in a jerky and disconcerting
manner around the chandeliers or bedposts in unfrequented living- or
bed-rooms. The relative proportion of these two genera in full summer
varies in different localities. Roughly speaking, out of 100 flies
collected in a house there is something between 90 and 99 per cent. of
_M. domestica_, but the numbers not only vary with locality, but with
temperature.
On the other hand, there is a curious disproportion between the number
of sexes found ‘at home’ in the lesser house-fly. For every 100 _F.
canicularis_ taken indoors seventy to seventy-five are males, the
numbers being evened by an equal preponderance of females who have
remained out of doors.
[Illustration: FIG. 24.—Larva of _F. canicularis_. (From Gordon
Hewitt’s Report to Local Government Board, 1912.) Magnified.]
The larva of _Fannia_ is a flattened-looking grub with distinct
segments, decorated by numerous feathery processes. It lives amongst
decaying vegetation and fruit, and also amongst fermenting animal
matter and dejecta. Sometimes it is found in rotting grass. As we shall
see later, it frequently passes into the human alimentary canal. _F.
scalaris_, usually known as the ‘latrine-fly,’ is even commoner than
its congener, and the external structural differences are minute. As
its name indicates, it is found as a rule breeding in human dejecta,
and is, therefore, as a typhoid carrier, much more dangerous than
_F. canicularis_. Its larva is also more commonly found in the human
intestine.
Then there are two species of large flies known as blue-bottles or
blow-flies—_Calliphora erythrocephala_ and _C. vomitoria_. The former
of these is the more common. The sides of its face are golden yellow,
set with black hair; whereas in _C. vomitoria_ the sides of the face
are black, but the hair is golden. Both are handsome, sturdy-looking
diptera, with bluish-black thoraces, and abdomens of a dark metallic
gun-metal sort of colour.
Blow-flies deposit their eggs on fresh or decaying flesh, and this is
one of the great sources of trouble to the officers of the Army Service
Corps. But they are not content with killed flesh. They will lay their
eggs on any living flesh which is exposed, or in sores or tumours, and
here their larvae will thrive. Dr. Graham-Smith tells us he once found
the exposed muscles of the broken leg of a living rabbit seething with
a mass of small blow-fly larvae, which were nourishing themselves upon
the living tissues.
[Illustration: FIG. 25.—Blow-fly or blue-bottle, _Calliphora
erythrocephala_, female (× 3). Antenna. Male head, dorsal view. Side
view of head. Natural size, resting position. (From Graham-Smith.)]
The eggs of the blow-fly hatch out in from ten to twenty hours in
normal British temperatures; the larval life, in its three stages,
lasts from seven to eight and a half days; the pupa state lasts a
fortnight, so that the total development extends a day or two over
three weeks. The maggots are unusually voracious; and Linnaeus used to
say that the progeny of three blow-flies will dispose of a dead horse
as quickly as three lions.
_C. erythrocephala_ is essentially an outdoor fly and enters houses
only in search of a nidus on which to deposit its eggs. _C. vomitoria_
resembles its congener in size and habits, but it is not so abundant.
Occasionally its eggs have been known to be deposited in the nostrils
of animals and men.
But there are:—
All species of resplendent flies,
Some with green bodies and green eyes,
Pricking like pins’ heads from their holes
Like tiny incandescent coals.
(ANON.)
[Illustration: FIG. 26.—Green-bottle, _Lucilia caesar_, male (× 3).
Antenna. Female head, dorsal view. Natural size, resting position.
(From Graham-Smith.)]
One of these, _Lucilia caesar_, is a marked nuisance to those
responsible for victualling a camp. This green-bottle fly, like the
_Calliphora_ and the house-fly, belongs to the family Muscidae, and its
larvae are said to be indistinguishable from those of blue-bottles.
Some species of _Lucilia_ deposit their eggs in great quantities
amongst the wool of sheep when the sheep are ill-kept, and they do much
damage. But as far as war is concerned the harm that _Lucilia_ does
is laying its eggs upon dead animals. It does this on all sorts of
meat-stores; but in times of peace it especially infests stale fish,
which the issuing larva very soon eat clean to the bone. When feeding
upon a dead fish lying upon a beach they burrow down in the sand below
their food. They descend some two to six inches, and for the most part
remain deep in the sand during the daytime, coming up to feed at
night. They also have a habit of migrating from one fish to another.
This fly has also been known to lay its eggs in the neglected wounds of
human beings.
[Illustration: FIG. 27.—Flesh-fly (_Sarcophaga carnaria_), female
(× 3). Antenna. Natural size, resting position. (From Graham-Smith.)]
_Sarcophaga carnaria_ is another species which occasionally infests
human sores, and which enters houses in search of filth or carrion on
which to lay its eggs; it is viviparous and produces not eggs but live
larvae. One female can give birth to 20,000 young; and Redi states
that the larvae of these flesh-flies will in twenty-four hours devour
so much food and grow so quickly that they increase their weight
two-hundredfold.
Finally, there is a group of flies whose larvae penetrate under the
skin of human beings and give rise to definite subcutaneous troubles.
But, fortunately, these are, with few exceptions, confined to the
warmer regions of the earth, and there is very little risk of their
causing real trouble in Northern or Central Europe.
[Illustration: FIG. 28.—Side view of blow-fly (_Calliphora
erythrocephala_) (× 5). A, Cheek (jowl); B, squama; C, halter.
(From Graham-Smith.)]
The troubles or diseases caused by the presence of fly larvae in the
body are grouped in medical language under the term ‘myiasis,’ which
Graham-Smith defines as follows:—
‘The term myiasis signifies the presence of dipterous larvae in the
living body (whether of man or animals), as well as the disorders
(whether accompanied or not by the destruction of tissue) caused
thereby. Though not strictly coming within this definition, the
sucking of blood by larvae through punctures of the skin, which they
themselves produce, may be included for the sake of convenience in
classification.
Myiasis in man may be produced by dipterous larvae:—
(_a_) Sucking blood through punctures in the skin (_Auchmeromyia
luteola_).
(_b_) Deposited in natural cavities of the body (_Chrysomyia_,
_Lucilia_, _Sarcophaga_, _Calliphora_, _Oestrus_).
(_c_) Deposited in neglected wounds (_Chrysomyia_, _Lucilia_,
_Sarcophaga_, _Calliphora_).
(_d_) Living in subcutaneous tissue (_Cordylobia_, _Dermatobia_,
_Bengalia_ (?), _Hypoderma_).
(_e_) Passing through the alimentary canal (_Fannia_, _Musca_,
_Eristalis_, _Syrphus_, _Gastrophilus_).
In the above list, only the more common genera producing myiasis are
mentioned. In England, Type (_e_) is fairly common, and Types (_b_) and
(_c_) are occasionally observed.’
We may now consider in detail, but very shortly, the categories set
forth by Dr. Graham-Smith:—
(_a_) The very peculiar blood-sucking maggot known as the
Congo-floor-maggot—the larva of _Auchmeromyia luteola_—fortunately
does not spread beyond tropical and sub-tropical Africa. It chiefly
affects the natives who sleep on mats.
(_b_) The flies which deposit their ova and larvae in the cavities of
the body are again mostly foreign. The worst of all is the screw-worm
(_Chrysomyia macellaria_) of the Southern States, Central and South
America. Although it extends to Canada it is not troublesome north of
Texas.
Occasionally, blow-flies in Great Britain deposit their ova in
the human nose or ear. They very rapidly hatch and cause great
inflammation and necrosis until they can be discharged or removed.
They have even been found in the anterior chamber of the eye; and I
have some microscopic sections showing the presence of these larvae
in that chamber, whither they had probably proceeded from the nasal
sinuses. But on the whole, cases of this sort are comparatively rare,
and cause but little trouble.
(_c_) The real difficulty, and one which late last summer proved a
serious trouble to our army in the field, are the cases in which
maggots were found in neglected wounds. Here, however, we may take
some comfort in the fact that the trouble is fortunately much greater
in the tropical and sub-tropical regions than in more temperate
climates, and diminishes as the cold weather draws on. Still, during
the hot weeks of last August there were cases of wounded soldiers
left lying on the fields for two or three days who were found to be
suffering in this way. One almost hesitates to offer suggestions to
our heroes in such cruel conditions; but whenever and wherever it can
be done wounds should as far as possible be kept covered.
Not only are neglected wounds affected, but tumours and ulcers are
often attacked. But, as I have said, the danger is much greater in
warmer climates. We know that Herod Agrippa ‘was eaten of worms, and
gave up the ghost’: a fact which recalls the translation given by an
undergraduate in difficulties with the Acts of the Apostles in the
‘Little-Go’ who rendered ‘καì γενóμενος σκωληκóβρωτος ἐξέψυξεν’ ‘He
became a Skolekobrote, and died in the enjoyment of that office.’
(_d_) Flies burrowing in the subcutaneous tissues are again very much
commoner in tropical climates than in Northern Europe, and the cases
quoted in our country are comparatively rare.
(_e_) The presence of larvae in the alimentary canal of man is by
no means uncommon. Both the larvae of _Musca_ and _Fannia_ are not
infrequently found; and over a thousand of the latter have been
passed by a highly infected individual at one time. They probably
make their way into the body with over-ripe fruit. In some cases
they give rise to no symptoms, but in others violent pains are felt
and a certain dizziness, and the digestive functions are interfered
with. The presence of these larvae in the urinary passages is even
more difficult to explain, but they undoubtedly are at times found in
these channels.
A few years ago an elaborate investigation was carried on by Mr. W.
Nicol, for the Local Government Board, on the part played by flies
in the dispersal of the eggs of parasitic worms. He showed quite
definitely that the ova of certain human parasites are taken into the
fly and pass through its body undigested. Should these be deposited
on the food of man, there is great risk of his becoming infected. As
I have said before, flies take only liquid food, and it is only when
the ova of the parasites are very small that they can pass into their
alimentary canals. Some eggs are too large for the fly to swallow. Eggs
of parasitic worms have also been shown to be carried on the legs and
proboscides of flies, and these are deposited on the spot where the
fly next cleans itself. Probably, however, in the end little harm is
really done by flies in disseminating parasitic worms, but it is a
possibility which must not be altogether disregarded.
The remedial measures for the control of flies are fully dealt with in
Graham-Smith’s admirable book, ‘Flies in Relation to Disease,’ from
which I have ventured to borrow many figures; and again by Dr. Gordon
Hewitt, in his work on ‘House-flies,’ which has had such a wonderful
success in stimulating our North-American cousins to decrease the
numbers of one of the gravest enemies to mankind.
It has been shown over and over again that we can control the mosquito:
the building of the Panama Canal alone proves this. We could equally
control the ‘Infinite Torment of Flies.’ The Canadians and Americans
are doing their best; but are we? The knowledgeable world has at least
discovered the reason why Beelzebub was called the ‘Lord of flies.’
CHAPTER VII
MITES
PART I
THE HARVEST-MITE (_Trombidium_)
Natura in minimis maxime miranda.
(LINNAEUS.)
WE do not know what life is, but we can at any rate record its
manifestations; and we know that it is always associated with an
extremely complex substance called by Purkinje ‘protoplasm.’ This
substance Huxley described as ‘the physical basis of life.’ Protoplasm,
though we know of what elements it is composed, defies accurate
analysis, and, indeed, is never the same for two minutes together. It
is constantly changing, it is in a state of flux and is, in effect,
a stream into which matter is continuously entering and continuously
leaving.
Protoplasm may be living, or it may be dead; and when dead it soon
undergoes dissolution; but there is no life without protoplasm.
Somewhere or other Dr. David Sharp has stated that of the total amount
of protoplasm ‘in being’ in the world, the active volume of the
life-material of our globe, at least one-half is wrapped up in the body
of insects. But insects only form one sub-group out of the several
which make up the great group _Arthropoda_, or those animals which are
distinguished from others by possessing externally jointed legs—that
is, jointed appendages. This group includes also the Crustacea, the
multi-segmented Centipedes, and the Arachnids or spider-like animals.
Insects, like aeroplanes, dominate the air; Crustacea, like submarines,
inhabit the water; the poet has passionately asked:—
Ah! who has seen the mailèd lobster rise,
Clap her broad wings and soaring claim the skies?
But the answer, in the language of those curious mammals the
politicians, is ‘in the negative.’ Crustaceans are essentially aquatic.
On the other hand, centipedes and spiders are earth-loving animals but
some have unhappily developed parasitic or pseudo-parasitic habits.
The last-named sub-group, the Arachnids, comprise many subdivisions.
There are the spiders, the harvest-men, the scorpions, the king-crabs,
and so on. But one of the most numerous of the subdivisions of the
group are the mites and ticks (_Acarina_). I have for years been trying
to find some organ or structure shared by insects and mites and ticks,
and not found in any other group of arthropods. If I could do this I
would invent a long polysyllabic word—with lots of Greek in it—which
would really be a short way of designating those arthropods which
convey disease to man.
[Illustration: FIG. 29—_Trombidium holosericeum._ Female,
dorsal view. × 20. (After Railliet.)]
The acarines are for the most part small, and they differ from spiders
in having no waist. In fact, the three divisions into which the body
of an arthropod is normally divided—head, thorax, and abdomen—are
indistinguishable in mites, the body forming an unconstricted whole. As
a rule, these little creatures breathe, as do insects, by tracheae, or,
if these be absent, by the general surface of the body. They live for
the most part on vegetable and animal juices, and their mouth-parts
are, as a rule, piercing and suctorial; but in some species the
appendages of the mouth are capable of biting as well as piercing. The
adults have typically eight legs. The larval stages are very numerous,
and at times six distinct moults of the skin are recognisable. With few
exceptions the larva emerges from the egg as a six-legged creature. In
fact mites undergo a metamorphosis which varies in complexity and in
completeness in different groups, and it is often one of the larval
stages which causes the greatest trouble to man.
[Illustration: FIG. 30.—_Leptus autumnalis_ = larva of
_Trombidium holosericeum_. Ventral view. × 100.
(After Railliet.)]
One of these six-legged larvae has been long known as the harvest-mite,
under the name of _Leptus autumnalis_. But this is not a real species,
and there is still considerable confusion as to what the exact status
of _Leptus autumnalis_, the harvest-mite, is. Probably the larvae of
several species are involved, but it seems pretty certain that in many
cases the larvae will grow up into specimens of the genus _Trombidium
holosericeum_, though a certain and at present unknown percentage of
the larvae will grow up into _Trombidium something-or-other-else_.
They are minute bright-scarlet little creatures—the Cardinals of the
Mite world—of a beautiful satiny red, decorated here and there with
blackish spots. The body of the adult is somewhat square, tapering
slightly to the hinder end. Both legs and body are covered with red
hairs. The eyes are borne on little stalks—like lighthouses. The legs
have six joints and end in two little claws. The male is usually
smaller and more feeble than the female, the latter reaching a length
of 3 mm. to 4 mm. The adults are commonly met with in the spring or
commencing summer. Apparently, they nourish themselves on vegetable
sap. The larval form of this species[11] is undoubtedly one of the
forms confused under the now discarded name of _Leptus autumnalis_.
When starving, the body is orbicular in outline, but it becomes oblong
when it is fed, and in this case it may attain a length of ½ mm. Its
colour is of a deep orange.
[Illustration: FIG. 31.—_Leptus autumnalis_, with the so-called
proboscis. Magnified. (After Gudden.)]
This harvest mite, or, as it is called in France _le rouget_, is
most troublesome at the end of summer or at the beginning of autumn,
when it is found in enormous numbers in grass and amongst many other
plants—gooseberries, raspberries, currants, haricot-beans, sorrel,
and elderberries. From these plants it passes on to any warm-blooded
animals: particularly it attacks small mammals. Hares, rabbits, and
moles are often covered with them, but they leave their victim,
should it be shot, as soon as the body chills. They are particularly
common in Great Britain and in the centre and west of France, and
in certain parts of Germany. These irritating little semi-parasites
may be dislodged by the application of petrol or benzine—both very
inflammable—and the itching they cause allayed by the application of
acid or alcoholic lotions.
[Illustration: FIG. 32.—_Leptus autumnalis_ (× 100). The so-called
proboscis is formed around the hypo-pharynx sunk into the skin. (After
Trouessart).]
Men working in the fields are frequently attacked. During September
1914, the soldiers of the Sixth Division, stationed in and about
Cambridge, and living in tents, suffered severely from their ‘bites.’
They mostly attacked the ankles, the wrists, and the neck, but they
rapidly extend over the body. If they be checked by the presence of any
stricture, such as a garter or wrist-band, they accumulate behind it,
and the irritation is accentuated. The presence of their hypo-pharynx
in the skin causes the surrounding tissues to harden and form a
cylindrical tube—the so-called proboscis.
The amount of trouble they cause varies very greatly in different
people. Children and women with soft skins suffer, as a rule,
most; but, as happens in the case of other biting insects, certain
individuals seem to be almost immune, whilst others suffer very
considerably. The trouble is caused by the mite implanting its
mouth-parts in the skin—preferably in the hair-follicles or the
sweat-glands. When it is once fixed it rarely moves. The body remains,
of course, on the surface of the skin as a little reddish-orange
point, scarcely perceptible unless many of them are congregated in the
same position. The effect of their presence is to produce a swelling
in the skin, which may be as large as a split pea, accompanied by an
intense itching and a smarting which banishes sleep. This leads to the
patient scratching, and this scratching is the departure-point of many
troubles. Scoriated papules appear and eczematous patches, and when
the mites are very numerous an erythema, named by Rubies _Erythema
autumnale_, supervenes. The skin near the point of puncture swells,
becomes red, sometimes almost purple, and irregular patches, which when
confluent, appear a centimetre in diameter.
These skin troubles, which may end in a kind of generalised eruption,
are accompanied by a rise of temperature and a certain—sometimes a
high—degree of fever. Besides men, dogs and cats suffer from these
pests; and in these domestic pets the parasites give rise to a miliary
eruption. Domestic cattle—sheep and horses—are also attacked. And,
according to some authorities, poultry are not only attacked but killed
by these parasites. The larvae apparently only lives a few days in the
skin of the victim.
As far as is known at present the larvae of _Trombidium_ convey no
protozoal disease; but there is a terrifying little creature, known
as the Kedana mite, which in some districts of Japan causes a serious
illness, with a mortality of some 70 per cent. Apparently, it does not
act as an inoculating agent itself, but the papule, surrounded by the
red area which forms as a result of its bite, changes to a pustule, and
this lesion becomes the point of entrance of bacteria which produce the
so-called ‘river’ or ‘flood’ fever. If these mites be carefully removed
the patient suffers no harm.
Another species of mite, _Pediculoides ventricosus_, lives in stalks
of cereals, and is very apt to attack labourers who are dealing with
grain. Their bites cause severe irritation, local swellings, reddening
of the epidermis, and fever. In this particular species the female
before she is fertilised has an elongated form 0·2 mm. in length and
0·07 mm. in breadth; but when fertilised the ovaries increase to such
an extent that the posterior end of the body becomes spherical. In
this respect it resembles that remarkable flea, the chigo or jigger.
The larvae are exceptional in being born with four legs instead of the
usual three, and they pair almost immediately after emerging from the
egg-shell.
[Illustration: FIG. 33.—_Pediculoides ventricosus._ Male, ventral view
(× 250). Female, before fertilisation (× 225). A, after fertilisation;
the abdomen has begun to swell (× 250). B, with abdomen fully swollen
(× 40). (After Laboulbène and Mégnin.)]
CHAPTER VIII
MITES
PART II
ENDO-PARASITIC MITES (_Demodex_, _Sarcoptes_)
Say what the use, were finer optics giv’n,
T’ inspect a mite, not comprehend the heav’n.
(POPE, _Essay on Man_.)
DEMODEX
WE have seen that harvest mites are wont to insert their heads—or
rather their mouth-parts—into the skin of human beings, but other
mites show less restraint, and insert their whole bodies. One of
these, the well-known _Demodex folliculorum_, is, according to Guiart
and Grimbert, ‘Le plus commun des parasites de l’homme et nous en
sommes presque tous porteurs.’ Without taking quite so gloomy a view,
_Demodex_ is undoubtedly widely distributed in the skin of mankind
and of other mammals.
[Illustration: FIG. 34.—(_a_) _Demodex_ in hair-follicle of dog;
magnified. (After Neumaun.) (_b_) _Demodex folliculorum_; highly
magnified. (After Railliet.)]
There are differences of opinion as to whether this form should be
split up into numerous species, or subspecies, according to the genus
of the mammals upon which it lives. We, at any rate, will confine
our attention to the human kind and so avoid losing ourselves in the
tortuous maze of synonymy and the arid discussion of a meticulous
classification so dear to the analytical German mind. To us a _Demodex_
shall be a _Demodex_, and we will leave it at that.
Unlike the majority of mites, _Demodex_ is a good deal longer than it
is broad. But even for a mite it is very small, and shows signs of
bodily degradation associated with its parasitic habit of life. Its
shape is adapted to its habitat, which is the sebaceous glands of the
skin. The long abdomen appears to be segmented, but the annulations are
not true segments. The legs are reduced to conical stumps. The male
is 300 µ[12] long and 40 µ broad across the cephalothorax. The female
is, as usual, larger, measuring 380 µ in length by 45 µ in breadth. The
minute larvae have, as is so often the case with mites, but three pairs
of legs, and are 60 µ to 100 µ in length.
This parasite, which lives on all parts of the skin of the human body,
is perhaps most commonly seen on the nose and in the passages leading
into the ear. It can be expressed by firmly pressing over the black
spot which indicates its presence in the skin of the nose or elsewhere
any small cylindrical tube, such as a watch-key. When expressed it is
not always easy to see, as coming away with it is a mass of sebaceous
matter which can best be dissolved off with oil on the microscopic
slide. Whether this particular parasite causes much disease is not
known. But in some cases it is certainly associated with acne and other
skin disorders; and as it is also found in hair-follicles, it may
possibly destroy the hair. It is apparently spread by personal contact.
THE ITCH-MITE
A much more serious trouble is due to _Sarcoptes scabiei_—often called
the Acarus—which gives rise to the disease known in England as the
‘itch’ and in France as the ‘_gale_.’
[Illustration: FIG. 35.—_Sarcoptes scabiei._ Female. × 180.
Ventral view. (From Bourguignon.)]
_Sarcoptes scabiei_ in both sexes is but little longer than broad.
The female is, as usual, larger than the male. These mites are shaped
very much like microscopic tortoises, of a pearly grey colour, passing
at parts into a rusty brown. Of the four pairs of legs two run
forward close to the head, and two point backwards. The integument is
semi-transparent and strengthened by parallel folds, and bears many
little bilaterally symmetrical protuberances and scales. There are also
certain hairs which have some systematic value.
[Illustration: FIG. 36.—_Sarcoptes scabiei_. Male. × 300. Ventral view.
The sucker on the fourth leg on the right is accidentally folded over
the third leg. (From Bourguignon.)]
The male is usually recognised by the fact that its third pair of legs
terminates in a long hair, whilst the other legs end in pedunculated
suckers.
[Illustration: FIG. 37.—One of the legs of _Sarcoptes scabiei_
(× about 450), showing the stalked sucker and the curious
‘cross-gartering.’ (After Bourguignon.)]
The male measures 200 µ to 235 µ in length, by 145 µ to 190 µ in
breadth. By preference, he lives under the scales which the presence of
the parasite produce on the human host. The female is markedly larger
than the male, measuring 330 µ to 450 µ in length by 250 µ to 350 µ
in breadth. Her two anterior legs end in stalked suckers, whilst the
two posterior end in hairs. The legs, like Malvolio’s, are curiously
‘cross-gartered’ with chitinous bars and rings.
At first she promenades about with the male on the surface of the human
skin, but when they have paired the female begins to tunnel in the
epidermis. The poor male, having been used, dies. As the mother-mite
tunnels she begins to lay eggs, leaving them one by one behind her as
she burrows deeper and deeper into the epidermis. Hence those that are
nearer the entrance of the tunnel are always more advanced in age and
development than those farther in. She always works head forward, and
as her tunnel is but slightly bigger than the breadth of her body, she
cannot turn round, and she is prevented from retreating by the backward
hairs or spines of her body. Hence she burrows always forward, until
she has dug her own grave at the far end of her excavation.
She is said to live two or three months and to lay one or two eggs a
day. Thus one female is, in time, enough to infect seriously a single
host. The egg is, relatively to the size of the mother, enormous: its
length being 150 µ and its width 100 µ. The egg is hatched out after
three to six days, and the young larva is hexapodous—that is, as is so
usual in Acarines, six-legged. It escapes from the burrow on to the
skin and soon tunnels into the epidermis of its host, where it moults
and transforms, about the ninth day, into a four-legged nymph. At the
end of another six days the mites moult again, and at this period one
can distinguish nymphs of two sizes: the larger female, and the smaller
male.
[Illustration: FIG. 38.—A diagrammatic view of the tunnel made by the
female of _Sarcoptes scabiei_, with the eggs she has laid behind her as
she burrows deeper and deeper. The black dots represent the excrement.
(After Guiart and Grimbert.)]
Within a month after hatching the _Sarcoptes_ has become adult, and the
sexes are occupied in seeking each other on the surface of the skin,
and it is in this stage that they are easily passed by personal contact
from one human being to another.
[Illustration: FIG. 39.—A female _Sarcoptes scabiei_, with four eggs
in different stages of development; × about 180. (After Bourguignon.)]
Many animals suffer from _Sarcoptes_; and the fact that this genus can
be transferred to man from the horse, the ox, the sheep, the goat, the
dog, the cat, the camel, the lion, &c., is a slight argument in favour
of their being one species. There is another undoubtedly distinct
species which causes serious epidemics, especially in Norway; but that
is hardly likely to enter into the scope of this book.
_Sarcoptes scabiei_, the itch-mite, is, however, a cause of serious
trouble in an army ‘in being.’ The tunnel or gallery in which the
female mite burrows is the only lesion produced directly by the
parasite. To the naked eye it presents a little whitish or greyish
line, varying in length from some millimetres to one or even three
centimetres, the longer ones occurring most frequently on the hands
or wrists. It is of course open at one end, and ends in a cul-de-sac,
which is slightly swollen, and here it is the female has taken up her
abode. She is visible as a small white, brilliant spot. Besides the
wrist, and the inner faces of the fingers—the interdigital areas—the
palms of the hands are most commonly affected.
If there is any doubt as to the cause of the existence of these
tunnels, a diagnosis can easily be verified by extracting the mite.
With the point of a needle, held almost parallel to the skin, the
tunnel can be slit open, and when the point has reached the inner
end the mite is very apt to seize it with its suckers, and can be so
withdrawn, and, if not, it can easily be picked out. It can then be
examined in a drop of diluted glycerine under a microscope.
I am no doctor, hence I venture to refer my readers to the article on
Scabies in the ‘Encyclopaedia Medica,’ by Dr. G. Pernet, and to quote
the following paragraphs from Dr. H. Radcliffe Crocker’s ‘Diseases of
the Skin,’ third edition, vol. ii.:—
_Symptoms of Pathology._—The clinical picture of scabies is made
up of two elements: the burrows, or cuniculi, and the attendant
inflammation excited directly by the _Acarus scabiei_[13]; and,
indirectly, the lesions produced by scratching, and the modifying
influences of pressure, friction, &c. The result is a great
multiformity of lesions, which, combined with their distribution,
is in itself suggestive of the nature of the disease, and enables a
practised eye to detect a well-marked case at a glance.
When the skin is first penetrated by the acarus, inflammation is
often set up, and a papule, vesicle, or pustule is the consequence.
These papules or small vesicles, individually indistinguishable
from eczema vesicles, are the most common form of eruption; but the
inflammatory symptoms are absent in many burrows. The tract extends
and forms a sinuous, irregular, or rarely straight line, which in
very clean people is white, but, as a rule, is brownish or blackish
from dirt being entangled in the slightly roughened epidermis; the
length of these burrows is generally from an eighth to half an inch,
but occasionally much longer—Hebra having noticed one four inches
long. When a pustule is formed, part of the burrow lies in the roof,
but the acarus is always well beyond the pustule or vesicle; or,
if there is none, lies at the far end, and with a lens may often be
discerned as a white speck in the epidermis. The degree and number of
inflammatory lesions vary much; there may be no inflammation at all
about many burrows, or the whole hand—especially in children—may be
covered by pustules, vesicles, or papules; and, indeed, a pustular
eruption on the hands is always strongly suggestive of scabies; there
is, however, no grouping or arrangement of any of the eruptions, as
in eczema, the lesions being scattered about irregularly. It must be
remembered that burrows are not always present, from various causes.
If the disease is recent it may not have got beyond the papular or
vesicular stage; while in washerwomen, bricklayers, or others whose
hands are constantly soaked in water or alkaline fluids, or who
have to scrub their hands violently, the burrows become destroyed.
The eruptions due to scratching have already been described in the
descriptions of the ‘scratched skin,’ and comprise excoriations,
erythema in parallel lines, eczema, impetiginous or so-called
ecthymatous eruptions and wheals, and the inflammatory scab-topped
papules often left after the subsidence of the wheals—especially in
children. In carmen, cobblers, tailors, and others who sit on hard
boards for hours together, pustular and scabbed eruptions, situated
over the ischial tuberosities, are so abundant and constant as to be
practically diagnostic of scabies in such people. Similar eruptions
may be seen where there is friction from trusses, belts, &c.
_Treatment._—I use in private practice, after the preliminary soaking
and scrubbing, naphthol 15 parts, cret. prep. 10 parts, sap. mollis
50 parts, adipis 100 parts, as recommended by Kaposi, well rubbed in.
For infants it can be used half-strength, and I omit the soft-soap. I
can speak of it in the highest praise. It is effectual, has no smell,
and is not liable to irritate the skin, as sulphur does. It is,
however, too expensive for public practice. Nephritis has occurred
from its over-use, but I have never seen any bad symptoms. Another
remedy less likely to irritate the skin than sulphur is balsam of
Peru, of which the vapour alone is said to be fatal to the acari. The
balsam is rubbed in for twenty minutes every night; a night-shirt
impregnated with the drug is worn, and in the morning an ordinary
soap-and-water bath is taken.
Colonel Allcock says that the best treatment for the itch ‘consists
in the free use of soap and hot water and the liberal application
of sulphur ointment, continued for several days. Some prefer baths
of potassa sulphurata (1 ounce of the salt to 4 gallons of water).
Clothing and bedding should be fumigated with sulphur or baked.’
ENDO-PARASITIC MITES
Certain little mites whose appearance is as repellent as their name—for
they are known as _Nephrophages sanguinarius_—were recorded by two
Japanese observers twenty years ago as coming away in the urine of a
Japanese patient who was suffering from various bladder troubles. As
the mites were in all cases dead, the Japanese doctors thought that
they must have been endo-parasites of the kidney. They were found day
after day for a week or more, and they were found also in the water
with which the bladder had been washed out, but always dead. It is, of
course, possible that the Japanese doctors were right in their surmise,
but the best that can be said for the case is that it is ‘not proven.’
[Illustration: FIG. 40.—_Nephrophages sanguinarius_ (enlarged). Male,
ventral surface. Female, dorsal aspect. (After Miyake and Seriba.)]
These awful-looking little mites are said to have two large eyes, and
legs of five segments and of equal length. Their colour is greenish
to brownish yellow. Undoubtedly there are many mites which live as
endo-parasites; certain members of the group Analgesinae, such as
_Laminosioptes gallinarum_, live in the intramuscular and subcutaneous
tissue of fowls, and _Cytoleichus sarcoptioides_ in their air-sacs. I
have myself found one of these species in the pigeon, so that it is
by no means beyond the bounds of human possibility that _Nephrophages
sanguinarius_ really lived in the tissues of the Japanese. Very strange
things live in the tissues of some Japanese.
CHAPTER IX
TICKS
A waterleche or a tyke hath neuer ynow, tyl it brestyth.
(_Jacob’s Well_, 1440.)
TICKS are mites ‘writ large,’ and until about the beginning of this
century they were regarded with what one might call mild disgust and
regret. Now, however, that they have been proved to play a part—and a
very important part—in the dissemination of disease, we have come to
regard them, as Calverley said we should regard the Decalogue, ‘with
feelings of reverence mingled with awe.’
The body of a tick is covered with a tough, smooth or crinkled skin,
capable almost of any amount of extension. Until they have fed they are
flattened in shape, but after a meal of blood they very soon lose the
outlines of a Don Quixote and attain those of a Sancho Panza. In the
adult, the legs are eight in number and have six joints ending in two
claws and sometimes in suckers. Some have eyes and some have no eyes.
[Illustration: FIG. 41.—Evolution of _Argas persicus_. 1, the egg; 2,
the six-legged larva; 3, the same gorged; 4, an unfed nymph; 5, nymph
gorged. (After Brumpt.)]
The most formidable part of their armour is, however, the mouth-parts,
consisting of the tactile pedipalps, and the piercing-probe which they
stick into our bodies. This probe consists of a dorsal membranous
sheath and a ventral hypostome armed with recurved teeth, forming
together a tube within which play two cutting and tearing chelicerae.
When these have cut a way into the flesh they are withdrawn, and
the tube is inserted into the wound and blood is pumped up it by
the sucking-pharynx. It is the teeth on the hypostome, and not the
chelicerae, which anchor the ticks to their prey.
Ticks, as they affect the soldier, may be divided into two families.
The first of these, the _Argasidae_, are usually associated with human
dwellings, fowl-houses, dove-cotes, and so on, and are more commonly
parasitic on fowls than on cattle or human beings. The members of this
group hide away in crevices and corners during the day, and come out at
night to feed, for ‘their deeds are evil.’
[Illustration: FIG. 42.—_Ixodes ricinus._ Mouth-parts of the female:
A, seen from the dorsal, B, from the ventral surface. The median,
dotted, portion of the left-hand figure is the sheath; the toothed
portion the hypostome. The lateral process is the pedipalp shown only
on one side. × 35. (After Nuttall and Warburton.)]
_Argas persicus_, known to travellers as the ‘teigne de miana,’ is of
an oval form, of brownish-red colour. The male measures 4 mm. to 5 mm.
in length by 3 mm. in breadth; the female 7 mm. to 10 mm. in length
by 5 mm. to 6 mm. in breadth. This creature frequents the northern
parts of Persia, and occurs in many other warm countries. In South
Africa it is known as the ‘tampan’ and ‘wandlius,’ where it is mainly a
fowl-parasite. In Persia it is very much dreaded, though probably the
effects of its bite are due to the unsuitable treatment the punctured
skin receives and the consequent invasion of the tissues by septic
bacteria. In South Africa it is frequently fatal to fowls, especially
to chickens; but the death is there believed to be due to the loss of
blood. It is definitely proved to convey Spirochaetosis.
We have not yet explained that ticks pass through several stages
as they advance from the egg to the adult. The larval stage of _A.
persicus_ will remain on its host for five days. It then leaves, and
moults in retirement. After the moulting it visits its host by night
and remains on it for about an hour. This second stage, known as the
‘nymph’ stage, moults twice, and the female in each stage becomes much
distended with blood—‘gorged,’ as the saying is. With each moult it
becomes larger, but otherwise does not alter much in appearance. The
adult female also, like the nymph, visits the host from time to time,
and between these visits deposits eggs in great quantities in sheltered
crevices—some 50 to 100 being deposited at once.
[Illustration: FIG. 43.—_Argas reflexus_, female. On the left the
dorsal view of a specimen laying eggs; on the right a ventral view
of the same. (After Brumpt.)]
_Argas reflexus_, the ‘marginated tick,’ is yellow and white—the Papal
colours. It is common near dove-cotes and pigeon-houses, and often
attacks people sleeping in their neighbourhood. Its bite causes much
irritation, and sometimes leads to vesicles and ulcers. At one time it
was very common in Canterbury Cathedral, and so worried the worshippers
that it took all the eloquence of the ‘Very Reverend the Dean’ to
overcome its repellent powers.
[Illustration: FIG. 44.—_Ornithodorus moubata_, an unfed female. To the
left a ventral, to the right a dorsal view, showing the crinkled skin.
(After Brumpt.)]
_Ornithodorus moubata_, sometimes known as the ‘tampan,’ occurs pretty
often in South Africa, and was a cause of considerable trouble to our
troops during the South African War. It lives normally in the shade of
vegetation, but frequently invades the native huts. It is catholic in
its taste and attacks most mammals, and it has a decided preference
for men. In Uganda the natives frequently die from its bites—dying of
so-called ‘tick-fever.’
[Illustration: FIG. 45.—_Ornithodorus moubata._ Female, gorged,
seen in profile. (After Brumpt.)]
I myself once assisted in identifying two ticks, in the nymph stage,
taken in Cambridge from the ear of an American visitor to this country,
who had been camping out in Arizona shortly before his arrival. This
tick turned out to be a species of _Ornithodorus megnini_, which, as
a rule, attacks the horse, the ass, and the ox about the ears. But
it frequently attacks man, and is well known in the United States,
infesting the ears of children. An allied species, _O. turicata_,
proves fatal to fowls in the Southern States and in Mexico, and is
very harmful to human beings. The chief harm that these ticks do is to
transmit protozoal diseases to man and other animals.
A very few ticks are said to be parthenogenetic, but by far the greater
part lay fertilised eggs, and lay them in considerable numbers; and the
eggs are agglutinated together in solid little masses, by the sticky
secretion of a cephalic gland, which opens below the rostrum. The eggs
are small and elliptical, and are laid to the number of many thousands.
The young tick, which is usually born with but three pairs of legs,
hatches out in a few days if the weather be warm, or a few weeks
should it prove cold. A certain amount of moisture must be present, or
the eggs are apt to dry up. These masses of eggs are laid on the ground
under herbs or grass, or on leaves.
[Illustration: FIG. 46.—_Ixodes ricinus._ The male is
inserting its rostrum in the female genital duct before
depositing its spermatophore. × 6. (From Brumpt.)]
The issuing six-legged larvae, like the young of other animals, are
very agile, climbing on to leaves and herbage. They passionately
wait with their front legs eagerly stretching out for the passage
of the host upon which they desire to settle. Of course, but one in
ten thousand succeeds, and it is terrible to think of the amount of
unsatisfied desire which must be going on in the tick world! The rest
perish miserably. Those that do succeed attach themselves to the skin
of the host, and thrust their rostrum and sucking-tube into the hole
already prepared by the cutting chelicerae. They suck the blood, and
when gorged fall to the earth, or in some cases remain on the host in a
state of inertia or apparent syncope.
Soon, however, the gorged larva moults, and gives rise to the first
nymph—an eight-legged creature. This affixes itself anew upon a
host—either upon the same or another one—again gorges itself, and in
all points resembles the adult, except from the fact that the sexual
orifice has not yet appeared. After some days the first nymph moults,
and then again remains either on the host or it falls to the ground.
In some cases there are two successive nymph forms; but as a rule the
first nymph gives rise by a second moult to the adult form, which
again for the third time regains a host. The adults are now ripe for
pairing, and the male having enlarged the orifice of the oviduct by
inserting its rostrum, deposits therein a spermatophore or capsule full
of spermatozoa. The female is often successively fertilised by several
males.
In many cases the male dies after fertilisation. The female swells
enormously when gorged, sometimes becoming as large as a filbert, or
even a small walnut. These ticks are seldom parasites of one particular
host, but attack many mammals indifferently. They have many natural
enemies: amongst the most important of which are certain hemipterous
insects whose female attacks the nymph of the _Ixodes_, and lays within
the body of the tick a number of eggs which develop inside the nymph
until they reach the adult stage, when they make their escape through
an orifice, generally at the hind end, leaving behind them the dead
body of their host. Three species of such Hemipterous insects are
known to be parasitic on ticks: of these _Ixodiphagus caucurtei_ is
ubiquitous. It attacks all kinds of ticks, but especially _Dermacentor
venustus_.
[Illustration: FIG. 47.—_Ixodiphagus caucurtei_ laying eggs
in the nymph of _Ixodes ricinus_. × 20. (After Brumpt.)]
_Ixodes ricinus_, of a brownish colour in the male, is very common
in England and, indeed, almost everywhere. The female is yellow and
flattened, somewhat resembling a grain of rice. It is the well-known
dog-tick, but it attacks oxen, goats, deer, horses, and man. It also
attacks the grouse, and is particularly common in some parts of Great
Britain. It is impossible to rid certain areas of these troublesome
guests. In some cases they produce tumours and introduce bacteria, and
in cattle it introduces an organism known as _Babesia bovis_, which is
the cause of haematuria in oxen. _Dermacentor venustus_ transmits Rocky
Mountain fever, which is common in certain parts of the States. The
fever is accompanied with pains in the joints and in the muscles and
an eruption on the surface of the skin, appearing first on the wrists
and forehead, and invading in time all parts of the body, followed by
a scaling of the skin during a period of convalescence. In Montana the
mortality caused by this disease is very high, varying in different
years from 33 to 75 per cent. In Idaho the mortality is far less, only
about 4 per cent.
_Ornithodorus moubata_ inoculates man with a spirochaete (_Spirochaeta
duttoni_), which is the agent of the African tick-fever or relapsing
fever. One of the curiosities about the organisms transmitted by
ticks is that they live through the whole cycle of the tick’s life.
If they are taken in by the larva they are only transmissible by the
following larval stage. If they are taken in by the nymph they are
only transmissible when again the nymph stage is met with, and the
same is true of the adult. Think what such a protozoon must have seen!
The fertilisation of the egg by the spermatozoon, the fusion of their
nuclei, the extrusion of the polar-bodies, the breaking up of the egg
into segments, the gradual building up of the tissues of the larva, the
sudden inrush of the host’s blood when the larva is safely fixed, the
moulting, the changes in the nymph, the development of the generative
organs, the formation of the eggs! What a text-book of embryology and
anatomy it could write if only it had descriptive powers! If I may
paraphrase Kipling:—
Think where ’e’s been,
Think what ’e’s seen,
Think of his future,
AND GAWD SAVE THE QUEEN!
CHAPTER X
LEECHES
PART I
THE MEDICINAL LEECH (_Hirudo medicinalis_)
Hardly anything real in the shop but the leeches and _they’re_
second-hand. (BOB SAWYER, _The Pickwick Papers_.)
AS Mr. W. A. Harding has pointed out, eleven species of fresh-water
leeches occur in these islands. But one of these, the _Hirudo
medicinalis_, seems to be vanishing, and yet it is just the one we
should cherish and preserve.
[Illustration: FIG. 48.—_Hirudo medicinalis_; about life size.
1, Mouth; 2, posterior sucker; 3, sensory papillae on the anterior
annulus of each segment. The remaining four annuli which make up
each true segment are indicated by the markings on the dorsal
surface.]
There are people who do not like leeches. This is shown by the
agitation amongst the travellers in an omnibus, as depicted in _Punch_
by Leech, years and years ago, when an old gentleman had upset a bottle
of them in their midst. But the medicinal leech, which is our theme, is
really the friend of man and of the soldier, and is a beneficial and
not a harmful animal. There are, of course, other leeches in our rivers
and in our seas, but of the latter our knowledge is scanty and it is
difficult to increase it at present—at any rate, in the Channel or in
the North Sea. In any case the marine leeches in our island-waters have
no human interest except the influence they exercise on our fish-food
supply, and this is practically negligible.
Zoologically speaking, leeches are undoubtedly degenerate earth worms
(_Oligochaeta_); and some very interesting ‘Zwischenformen’—like Mr.
Vincent Crummles, I am ‘not a Prussian’; but in spite of the war, we
may as well employ a useful term captured from the enemy—have been
found in Russia and Siberia: forms which combine many of the characters
of the _Oligochaeta_ and the _Hirudinea_. Possibly the degeneracy which
leeches are said to exhibit is associated with a semi-parasitic habit
of life. But a semi-parasitic habit does not apply to all leeches—in
fact, it applies but to few genera; there are many others, equally
degenerate—if degenerate they be—who have no trace of semi-parasitism.
A curious thing about leeches is that all the varying genera have the
same number of somites or segments; and though some of these segments
or somites are masked and fused, when analysed by the number of
segments in the embryo, by the number of the nerve ganglia, and so on,
leeches seem always to have thirty-four such segments. These do not
correspond with the rings or annulations so visible on the outside;
but a certain number of these annulations, varying in each species,
‘go’ to each somite, and so constant are these numbers that it would
not be very difficult to represent any given species of leech by a
mathematical formula.
The known species readily fall into two sub-orders: (1) The
_Rhynchobdellae_, which are marine and fresh-water leeches with
colourless blood, with no jaws, and with an extensile proboscis; and
(2) the _Arhynchobdellae_, which are all fresh-water or terrestrial,
with red blood, and generally with jaws. There is no extensile
proboscis, and the anterior sucker has a ventral aspect, and is in no
way distinct from the body. There are always in this group seventeen
pairs of nephridia or kidneys. We shall have mostly to do with the
latter sub-order.
[Illustration: FIG. 49.—View of the internal organs of _Hirudo
medicinalis_. On the left side the alimentary canal is shown, but the
right half of this organ has been removed to show the excretory and
reproductive organs. 1, Head, with eye-spots; 2, muscular pharynx;
3, first diverticulum of the crop; 4, eleventh diverticulum of the
crop; 5, stomach; 6, rectum; 7, anus; 8, cerebral ganglia; 9, ventral
nerve-cord; 10, nephridium; 11, lateral blood-vessel; 12, testis;
13, vas deferens; 14, prostate; 15, penis; 16, ovary; 17, uterus,
a dilatation formed by the conjoined oviducts.]
_Hirudo medicinalis_, the medicinal leech, is found in stagnant waters
throughout Europe and the western parts of Asia. It is rather commoner
in the southern parts of Europe than in the north. It used to be common
enough in England, where at one time, it was bred; but already a
hundred years ago its numbers were diminishing.
In a treatise on the Medicinal Leech, published by J. R. Johnson in the
year 1816, he records: ‘Formerly the species was very abundant in our
island; but from their present scarcity, owing to their being more in
request among medical men, and to the rapid improvements which have of
late years taken place in agriculture—particularly in the draining and
cultivation of waste lands—we are obliged to receive a supply from the
Continent, chiefly from Bordeaux and Lisbon.’ In his time he considered
that for every native leech employed at least a hundred foreigners were
used.
The same scarcity was very apparent to the poet Wordsworth,
whose insatiate curiosity is recorded in the following lines in
1802—Wordsworth was always asking rather fatuous questions:—
My question eagerly did I renew,
‘How is it that you live, and what is it you do?’
He with a smile did then his words repeat:
And said that, gathering leeches, far and wide
He travelled; stirring thus about his feet
The waters of the pools where they abide.
‘Once I could meet with them on every side;
But they have dwindled long by slow decay;
Yet still I persevere, and find them where I may.’
In Europe, where the leech was once very abundant, it is now chiefly
confined to the south and east, and in Germany it is still found in
the island of Borkum and in Thuringia—but just now we need not trouble
ourselves very much about their distribution in Germany.
In 1842, leeches were occasionally found in the neighbourhood of
Norwich, and there are villagers still living in Heacham in Norfolk who
remember the artificial leech-ponds. In the middle of the last century
the medicinal leeches ‘of late years ... have become scarce.’ At about
the same time, it is also recorded that they were becoming scarce,
though still to be found, in Ireland. Apparently this species is now
almost extinct in England, although I know of a naturalist who can
still find them in the New Forest, but he will not tell where. If they
were getting scarce in the beginning of the nineteenth century they are
far scarcer now[14]—_for there is no leech in London_—at least, there
are only a dozen or two, and they, like those of the firm ‘Sawyer late
Nockemorf,’ are second-hand and I have heard that there is a similar
shortage in North America. And yet leeches are wanted by doctors!
Harding tells us that:—
_Hirudo medicinalis_ is not the only leech which has been used in
phlebotomy. _Hirudo troctina_ (Johnson, 1816), occurring in North
Africa and in Southern Europe, where it is perhaps an introduced
species, was largely imported at one time for medical uses....
Several other species have been used for blood-letting in different
countries. _Limnatis (Poecilobdella) granulosa_ in India, _Liostoma
officinalis_ in Mexico, _Hirudo nipponia_ in Japan (Whitman), and
_Macrobdella decora_ in the United States (Verrill), are or have been
used in phlebotomy.
‘Our chief hope seems to lie in India.’ These words I wrote in October
1914, and my hopes were justified. Owing to the energy of Dr. Annandale
of the Indian Museum, and the anxious care of the authorities of the
P. & O. Company, I was able to land, early in the present year, a
consignment of many hundred _Limnatis granulosa_—in sound health, good
spirits, and obviously anxious to do their duty.
Leeches are still used much more than the public are aware. One
pharmaceutical chemist in the West End of London tells me he sells
between one and two thousand a year; and as they are bought wholesale
at about one penny each and sold retail at about sixpence, there is
some small profit.
[Illustration: FIG. 50.—Head of a leech, _Hirudo medicinalis_,
opened ventrally to show the three teeth and the pharynx _p_,
with its muscles; _s_, a nephridium.]
Leeches were well known to the ancients, and it would be easy to quote
case after case from the classical medical authorities of their use
in fevers and headaches and for many ill-defined swellings. They were
frequently used for blood-letting where a cupping-glass was out of the
question. With his curious uncritical instinct, Pliny records that the
ashes of a leech sprinkled over a hirsute area or formed into a paste
with vinegar and applied to the part will remove hair from any region
of the body. Leeches were also used by the Greek and Roman physicians
in angina—especially when accompanied by dyspnoea.
Probably the traffic in leeches reached its height in the first half
of the nineteenth century. Harding reminds us that in the year 1832
Ébrard records that 57,500,000 of these annelids were imported into
France, and by this time the artificial cultivation of leeches had
become a very profitable industry. Although in a small way leeches may
have been cultivated in special ponds in Great Britain, the English
never undertook the industry on a large scale. In Ireland the natives
used to gather the leeches in Lough Mask, and other inland lakes, by
sitting on the edge of the pool dangling their legs in the water until
the leeches had fastened on them. But the native supply was totally
inadequate, and the great majority of leeches used in this country were
then imported. In 1842 Brightwell mentions a dealer in Norwich who
always kept a stock of 5000 of these annelids in two large tanks. The
traffic, as we have seen, was very considerable.
The French leech-merchants recognised five classes, as follows:—
1. Les filets ou petites Sangsues, qui ont de un à cinq ans;
2. Les petites moyennes, qui ont de cinq à huit ans;
3. Les grosses moyennes, qui ont de huit à douze ans;
4. Les mères Sangsues ou les grosses, qui sont tout à fait adultes;
5. Les Sangsues vaches, dont la taille est énorme.
They also recognised many colour-varieties, of which we need only
mention the speckled, or German leech—‘Sangsues grise medicinalis,’
with a greenish-yellow ventral surface spotted with black, and the
green Hungarian leech with olive-green spotted ventral surface. Both
are merely colour-varieties of _Hirudo medicinalis_—a species which
shows great variation in colour, and often forms colour-races when bred
artificially.
The varying sizes of the five categories mentioned above may be seen
by the fact that one thousand of ‘les filets’ weigh from 325 to 500
grammes, one thousand of ‘les petites moyennes’ weigh 500 to 700
grammes, one thousand of the ‘grosses moyennes’ weigh 700 to 1300
grammes, and one thousand of the ‘grosses’ 1300 to 2500 or even to 3000
grammes. Whereas one thousand of ‘les vaches’ weigh up to 10 kilograms,
and sometimes even more. To increase their weight the dishonest dealer
sometimes gives them a heavy meal just before selling them.
[Illustration: FIG. 51.—_Hirudo medicinalis._ _o_, Anterior sucker
covering triradiate mouth; _e_ points to an annulus midway between the
male and female openings, _s_ to a nephridium, _u_ to the bladder of
the latter; _a_, anus. Four testes and four lateral diverticula of the
crop are also shown.]