a small wooden building tightly ceiled and with the windows and doors
closely screened so that no mosquitoes could enter. In this house,
during a total of sixty-three days, seven non-immune men were kept.
These men slept in beds furnished with the unwashed pillow-slips,
sheets, and blankets that had previously been used on the beds of
genuine yellow fever patients in Havana and elsewhere. This bedding was
actually stained with the excretions of the fever patients. Neither
during that time nor subsequently did one of these seven men develop
a case of yellow fever. This indicated to the surgeons, beyond much
question, that yellow fever is not carried in clothing, as had always
been held.
“Another house was built in this same field and divided into two
rooms by means of a wire screen extending from floor to ceiling. The
doors and windows of each room were closely screened with fine wire
netting so that no mosquitoes could enter. All bedding and material
carried into the rooms were disinfected by steam, which precluded any
possibility of the yellow fever germ being present in the bedding or
clothing.
“In one of the rooms, mosquitoes of a certain kind that had previously
bitten patients sick with yellow fever were placed. In the other room
none were allowed. Non-immune men were placed in both rooms. Of those
in the room containing no mosquitoes, not one had yellow fever. Of
those in the other room that were bitten by the infected mosquitoes,
six out of seven developed cases of genuine yellow fever. This
indicated beyond much question that mosquitoes were transmitters of
this disease.
“These experiments have been extended and duplicated many times with
the same results, so that we are justified in believing that a certain
mosquito known as _Aedes calopus_ is the sole and only agent in the
transmission of yellow fever.”
Dr. Lazear died from fever during the course of the experiments--a true
martyr of medical science--and Dr. Carroll came very near losing his
life also, following the bite of an experimentally infected mosquito.
Among other things, it was discovered that a mosquito may bite a
person suffering from yellow fever without becoming infected, unless
the bite occurs during the first three or four days of illness--later
than this the poison is not present in the blood. Another interesting
fact is that the _Aedes_ cannot infect anyone until at least twelve
days after it has received the virus from a sufferer, but after this
period it remains infected for a long time, and may give the disease to
a large number of people.
The actual cause of yellow fever is as yet undiscovered. As Herrick
says, “it is either too small to be seen with any lens now made or
it inhabits some organs of the body not suspected, or its habits are
entirely different from any other parasite with which we are familiar.
In any case the germ has eluded all efforts to locate it and scientists
are still ignorant regarding its real nature, habits, and appearance.”
It has been supposed that the yellow fever organism is similar to the
protozoan which produces malaria, but we do not know. Very little of
importance has been learned about the disease or the mosquito since
the Cuba commission in 1900, but wonderful progress has been made in
the application of such information as we have. By 1902 Havana was
entirely free from the yellow fever, and Rio de Janeiro, which had been
a fever-hell for many years, eliminated the disease entirely after a
six-year fight with the mosquitoes. In the Panama Canal Zone an army
surgeon named Gorgas was very successful in combating both yellow
fever and malaria. Although the United States has never suffered as
the tropical countries have, there have been numerous epidemics, the
last of which broke out in New Orleans in 1905. Vigorous anti-mosquito
campaigns were waged and the plague stamped out in a short time. The
tiger mosquito is still common all over the South, but there are no
yellow fever patients for them to bite. When a case does appear--some
sailor from the tropics, usually--he is seized by the Public Health
Service people and placed where no mosquito can get at him, and thus
it has not been necessary to wage a general exterminative war on the
yellow fever mosquito.
When the situation gets out of hand vigorous measures for the temporary
and local eradication of the insect are of course necessary. As Brues
says: “The success of this campaign has undoubtedly sounded the death
knell of the yellow fever epidemic and panic in the United States, for
New Orleans has amply demonstrated what may be accomplished in the
control of an epidemic by an efficient group of workers backed by a
sympathetic public and supplied with reasonable funds. Even in parts
of the tropics where it persists throughout the year, it is being
rapidly and permanently eliminated. Indeed, it bids fair to be the
first disease actually to become extinct as a direct result of human
discovery and applied science.”
There is, so far as is known, no satisfactory method of destroying
mosquitoes in the adult state, so that in the war against this pest we
must direct our efforts against the eggs and young. Herrick tells us
that “the methods taken to destroy mosquitoes fall into three distinct
classes; namely, the draining of bodies of water liable to contain eggs
and wrigglers, the application of oil to bodies of water that cannot
be drained and the introduction of fish into pools that cannot be
drained or oiled.”
Probably the best way to rid one’s immediate vicinity of mosquitoes
is to drain all marshes, pools and open receptacles. The drying up of
a few acres of swamp land may cause a marked fall in the death-rate
of an entire neighborhood, particularly in regions where malaria is
prevalent. The exposure of open tanks, reservoirs and barrels in which
stagnant water stands is no less than criminal in some parts of the
South.
Very often, for economic reasons, it is not practical to drain a
swamp or to eliminate open sewage ditches. In such cases we may take
advantage of the fact that the larvae of mosquitoes do not breathe by
gills, but are forced to come to the top for air. If ordinary kerosene
oil is sprayed upon the surface of the water, it spreads to form a
thin film which the larva cannot penetrate with their breathing tubes,
and so are drowned. The kerosene also destroys the floating eggs, and
kills the female mosquitoes as fast as they attempt to deposit. Crude
petroleum has been used instead of kerosene, but it does not spread as
well, and is very little cheaper. According to Herrick, one ounce of
kerosene is enough for fifteen square feet of water surface, and half a
teacupful is plenty for a barrel of water. The most convenient way to
apply the oil to small pools and ditches is by means of a five-gallon
tank carried knapsack fashion, with a short hose and nozzle. As the
entire development of the mosquito from egg to laying female seldom
requires more than eighteen or twenty days, it is best to use the oil
once every two weeks during the mosquito season. It would seem that
an easier way to get kerosene into the sewage ditches would be simply
to pour it into the water closet, and this has proven successful in
cases where there is little or no current; on the whole, however, the
surface-spraying system is best.
Ornamental ponds and pools cannot be drained or sprayed with oil, and
the same may be said of artificial ponds where domestic animals drink.
In these cases the mosquito pest may be mitigated by introducing fish
or other small creatures which feed upon the larvae. In Japan, and
more recently in other countries, the goldfish has been found very
satisfactory for this purpose. Various species of shiners, sunfish and
top minnows have also been used. W. P. Seal, who has given a great
deal of attention to this phase of the mosquito problem, states his
results as follows: “The writer has come to the conclusion, after
many experiments in small ponds, that a combination of the goldfish,
which is ornamental and useful in the open water, the roach or shiner,
which is a very active species, two small species of sunfish, which
live among plants, and the top minnow would probably prove to be more
effective in preventing mosquitoes breeding than any other fishes.”
Vernon Kellogg, Tillyard and others have studied the habits of
dragonflies in this connection, and the latter particularly has
emphasized their value as destroyers of mosquito larvae. He saw
a single dragonfly larva eat sixty wrigglers in ten minutes, and
captured an adult dragonfly which had over a hundred mosquitoes in
its mouth--so many that the mouth could not be closed. “I believe that
a successful checking of the mosquito pest in the ornamental waters
of parks and gardens could be readily obtained by the introduction of
dragonflies whose larvae, as well as the adults, would prey upon the
nuisance.”
The use of wire screens to exclude flies and mosquitoes from dwellings
is now well-nigh universal in most parts of the United States, although
there are still many rural communities in the South in which it
appears to be quite unknown. To keep out ordinary mosquitoes the wire
should have at least fourteen meshes to the inch, and the yellow fever
mosquito will pass through any screen which has less than eighteen
meshes. It is practically impossible to fit screens and frames well
enough to exclude all mosquitoes, but it is certainly better to contend
with a few stray mosquitoes in a screened house than to do battle with
the myriads of pests which swarm into an unscreened domicile. The
fewer the bites one receives, the fewer the chances of being bitten by
an infected mosquito; the fewer infected bites, the less severe the
resulting illness will be.
In many Southern cities the use of bed nets of bobbinet or mosquito bar
has now become quite general. There is usually a kind of wire frame
over the bed, and the net is sometimes tucked under the mattress all
round, while in other cases it is long enough to reach the floor on all
sides. Many travelers who must visit small towns, where the hotel bed
nets are lacking or unsatisfactory, carry their own nets, and set them
up every night to suit their fancy. Dr. Ross says: “Perhaps our first
and best defense against malaria lies in the habitual and scrupulous
use of mosquito nets at night.... The first care of the resident in the
tropics, of the traveler, the sportsman, the soldier, the miner, the
clerk, should be for his mosquito net. Wherever he lives, wherever he
goes, he should see that his mosquito net is with him, that it is in
good order, and that it is properly arranged at bedtime.”
There are several chemical substances used in driving mosquitoes out
of houses. One may rid a room of mosquitoes by the fumes of burning
sulphur, but the gas often discolors articles painted with lead
paint, and tarnishes gilt furniture and brass bedsteads. A vegetable
powder sold as pyrethrum, buhach, or Persian insect powder is made of
chrysanthemums, and is fairly effective when scattered about or blown
into cracks and crevices. It may also be burned as a smudge, but the
fumes are not as effective as those of sulphur. Many of the mosquitoes
fall to the floor in a stupor, and must be gathered up and burned, as
otherwise they will revive in an hour or so. Another fumigant much in
favor in New Orleans is a mixture of carbolic acid and gum camphor,
and is known as culicide. A heavy reddish liquid, it is evaporated by
heating slightly over a gas burner or alcohol lamp. The mixture is
inflammable but not explosive, and the fumes are not dangerous to human
life.
Hunters and campers often smear their hands and faces with various
substances supposed to discourage mosquitoes, oil of citronella being
one of the most popular. Camphor, cedar oil, kerosene and mixtures of
these substances in various proportions are also used, besides several
patented smudges and ointments. I have tried several of these, but
found them unsatisfactory. Tobacco-smoke helps a little sometimes, and
is at least free from the unpleasant and even nauseating odors of the
other mosquito repellants.
LIFE AMONG THE BEDBUGS
The bedbug (_Cimex lectularius_) has been known to man for a long
time, and has probably, as Herrick remarks, “been man’s bedfellow as
long as man has slept in beds,” if not longer. The ancient Romans
were intimately acquainted with this insect, and Pliny recommends a
mixture of macerated bedbugs in water as a cure for snake bites. It
is common in all parts of the civilized world, and doubtless came to
America with our sturdy fathers--even the Mayflower probably carried
a full cargo of bedbugs. Like its relative the stink bug, _Cimex_ has
a peculiar odor which is quite noticeable in small rooms where the
insects are unusually abundant. The full-grown bedbug is a flat-bodied,
mahogany-colored creature, with mouthparts admirably adapted to
blood-sucking. It lives in beds, window casings, cracks in floors,
etc., or in any article of furniture which affords a crevice large
enough to contain it. What we know about the insect’s life history
is mainly due to Marlatt, who did his work in 1896, and to Girault,
who carried out some further investigations some ten years later. The
eggs are very small, white and oval, and are, according to Herrick,
“laid in batches of varying numbers in cracks and crevices in the
bedsteads or other places where the bedbugs happen to be. The number of
eggs deposited by a single female is not known. Southall, Riley, and
others have made the common statement, probably not based on actual
observation, that each female lays about four batches of fifty each
during the season. Girault actually succeeded in obtaining 111 eggs
from one well-fed female between June 17 and August 19. How many she
had deposited previous to confinement for the experiment he was, of
course, unable to say. Girault’s experience with this one bug indicates
that the females may continue to lay eggs at different periods
throughout the breeding season and that there is only one generation a
year.”
The eggs hatch in about ten days, and the young bugs appear very much
like their parents--bedbugs do not pass through larva and pupa stages
like flies and mosquitoes. Bedbugs probably eat nothing but blood,
and a young individual, if properly supplied with this food, reaches
maturity in about six weeks, shedding their skins at least five times
during the period of growth. It is said that the bug feeds but once
between moults; if this is true the occupant of the bed must suffer
at least five bites in order to rear a single bedbug to maturity.
Bugs very much like _Cimex_ are found upon swallows, chimney swifts,
pigeons and martins, and many people believe that genuine bedbugs
are distributed by these birds, but this is probably not the case.
True bedbugs have never been found upon them, and although the “bird
bedbugs” are occasionally found in houses they do not seem to enter
beds and bite human beings. Bedbugs have, however, been found in
chicken houses, where they presumably bite chickens, so that there
is nothing inherently unreasonable in the view that they may be
distributed by birds.
The bedbug almost invariably lies hidden during the day, or as long as
there is a bright light in the room. As soon as the light is turned off
they sally forth to attack an exposed portion of the sleeper’s body.
It seems that they are particularly likely to be secreted about the
pillow, and as soon as the room is dark hit upon the neck as the most
desirable and accessible part of the victim’s anatomy. Only one who has
had personal experience in these matters can appreciate the vigor of
the onslaught, and the astounding rapidity with which the enemy whisks
out of sight the moment the light is flashed on. The bedbug’s bite is
not poisonous, and the pain is probably due only to the puncture, but
this is sufficient to cause considerable irritation and swelling.
Elie Metschnikoff, the author of that fascinating book entitled _The
Nature of Man_, was the first to call attention to the bedbug’s
possibilities as a carrier of disease germs. Bedbugs have been made,
under laboratory conditions, to transmit typhoid and other fevers,
and a tropical disease called _kala-azar_, but it has never been
demonstrated that the bugs actually do, under ordinary conditions,
play any part in the diffusion of these diseases. “Many writers and
experimenters,” writes Herrick, “have labored hard to prove this insect
guilty of graver offenses than that of simply stealing blood from human
hosts. The most they have been able to do so far, however, is to show
that in one case, at least, the bite of the bedbug formed a starting
point for a case of bubonic plague. As a matter of fact, this is really
a stronger indictment against the bedbug than, at first thought, might
appear. The sores resulting from bedbug bites offer ideal points of
entrance for disease-producing organisms and are a source of real
danger. Actual and definite proof that the bedbug transmits disease
is very difficult to obtain, but suspicion points strongly in that
direction.... It is extremely desirable to avoid the bites of this
insect if possible, especially in hotels where beds are occupied by so
many different people; but this is very hard to do, in fact, almost
impossible if one travels much.”
Luckily the bedbug is wingless, and therefore much easier to control
than winged pests like the fly and mosquito. If _Cimex_ were able to
fly there would be no keeping him out, as the newly hatched young could
pass through practically any sort of screen. The use of metal bedsteads
puts the bugs at a disadvantage because they afford fewer cracks and
crevices than those built of wood. Boiling water poured into the
crevices kills both eggs and bugs, but a more convenient method is to
use an oil can or squirt-gun filled with gasoline, kerosene, turpentine
or alcohol. The easiest way to rid a room completely of insects is to
fumigate with hydrocyanic acid gas, made by pouring dilute sulphuric
acid on potassium cyanide. This gas kills every living creature in
the room, but it is dangerous in the hands of careless or thoughtless
persons.
LICE, CRABS AND COOTIES
Lice have been associated with human beings as far back as our
historical records go, and are mentioned in the writings of Aristotle,
Herodotus and other ancient writers. Ordinarily cleanly and
well-dressed people today would be horrified to find lice about their
persons, as they are now confined to soldiers and others who do not
keep their bodies and clothing clean, but a few hundred years ago,
when everybody was dirty, they thought nothing of it. Samuel Pepys, an
English diarist of the seventeenth century, made the following laconic
entry in 1668: “Up betimes, finding our beds good, but lousy, which did
make us merry,” and there are many other matter-of-fact references to
these vermin in the literature of the period.
There are three common species, but they are all essentially alike in
structure, being small, wingless and provided with piercing and sucking
mouthparts. Schiödte describes the behavior of a louse on the back of
his hand: “Scarcely does the abominable little monster feel the heat
of the skin before it lays aside its former disheartened attitude,
and begins to feel at ease, its antennae oscillate for joy, and it
stretches all six legs complacently out from the body. But though the
pleasure and surprise at the sudden transportation into congenial
surroundings for the first moment eclipse everything else, hunger
soon asserts its claim, sharpened as it is by the long fast, which
has rendered its stomach and intestines quite transparent. The animal
raises itself on its legs, walks a few steps, seeking and feeling its
way with its antennae, while we follow it with a magnifier. Presently
it stops, draws in its legs a little, arches its back, bends the head
down toward the skin at an oblique angle, while it probes a small dark
and narrow organ repeatedly forward, and draws it back through the fore
end of the head; at last it stands still, with the point of the head
firmly abutted against the skin.”
All three of our species are blood-suckers, and are strictly human
parasites, being found only occasionally upon the bodies of animals
other than man. It is said, however, that they are sometimes carried
about by flies.
The head louse (_Pediculus capitis_) is usually found among the hairs
on the head, occurring elsewhere only occasionally. The female is about
one-twelfth of an inch long, while the male is only about one-half
as large; both sexes are grayish in color, but it is said that this
varies with the color of the host. Herrick quotes Murray to the effect
that lice on West Africans are black, those on Chinese yellow, those
on Hindoos smoky brown, and so on. The eggs are fastened to the hairs
by a gelatinous secretion, and the female has been known to deposit at
least fifty eggs in the course of a week. The period of incubation is
usually five or six days, and the young louse reaches maturity in a
fortnight. The movements and bites of these creatures are irritating in
the extreme, and the sufferer is sure to scratch so incessantly that
the scalp is always in an inflamed condition. The head louse is not
known, however, to carry any disease-producing organism.
The best way to get rid of the head louse, according to a circular
memorandum prepared under the direction of Surgeon General M. W.
Ireland, of the United States army, is to “clip the hair of the head
with a hair clipper and wash with a mixture of equal parts of kerosene
and vinegar. This should be followed in a few hours with a bath of soap
and hot water.... The hair should be caught in bags and burned. In
order to reduce the liability to infestation, the hair should be kept
close at all times.” Sulphur ointment may be used without sacrificing
the hair, but it is not so effective as the kerosene mixture.
The body louse (_Pediculus corporis_), known also as the gray-back and
the cootie, is somewhat larger than the head louse, and is usually
of a dirty white color. These creatures dwell in the seams and folds
of clothing, and are therefore known to some writers as _Pediculus
vestimenti_. They are difficult to find and to dislodge, as they do
not often cling long to the skin, but retire to their hiding places
in the clothing as soon as their blood-sucking is done. The eggs are
laid in the seams and wrinkles of the clothing, that made of wool being
given the preference. When one has no opportunity to change or wash
one’s clothes the pests become so abundant as to be quite unbearable.
Soldiers, inmates of prison camps and such people are particularly
liable to be abundantly supplied with body lice; they may pass from one
person to another when the bodies are brought into actual contact, or
one may become infested by sleeping in louse-ridden beds.
The Dutch scientist Leeuwenhoek, more than two hundred years ago,
carried out some experiments which are pleasantly reviewed by Herrick:
“Leeuwenhoek ... made an attempt to find out something definite about
the life history and rate of development of the body louse. He did not
believe the popular saying that a louse could become a grandfather in
twenty-four hours. At first he thought of hiring some person to act as
host for the lice. Later he changed his mind, overcame his own natural
aversion to these pests, and enclosed two large females within a fine
black stocking, the top of which he fastened tightly around his leg
above the knee. Here he allowed the two lice to live for six days and
obtain their sustenance from his leg. At the end of this period he
removed the stocking and found fifty eggs around one of the females
and forty eggs in another part of the stocking, evidently laid by the
second female, which, however, had escaped. He wore the stocking for
yet ten days, when on examination he found twenty-five young lice which
so disgusted him and dampened his enthusiasm that he threw the whole
thing into the street. Since Leeuwenhoek’s time the author is not aware
that any scientist has ever tried in the same way to study the life
history of these lice.”
[Illustration: