P. /BV

A FEW GENERAL DIRECTIONS

WITH REGARD TO

DESTROYING MOSQUITOES,

PA»TICCt.ARLY THR

YELLOW FEVER MOSQUITO.

W. C. GORGAS,

Colonel, Medical Corps, U. S. Army.

WASHINGTON:

GOVERNMENT PRINTING OFFICE.

1904.

A FEW GENERAL DIRECTIONS

WITH REGARD TO

DESTROYING MOSQUITOES,

PARTICULARLY THE

YELLOW FEVER MOSQUITO.

W. C. GOEGAS,

Colonel, Medical Corps, U. S. Army.

WASHINGTON:

GOVERNMENT PRINTING OFFICE.
1904.

A FEW GENERAL DIRECTIONS WITH REGARD TO DESTROYING
MOSQUITOES, PARTICULARLY THE YELLOW FEVER MOSQUITO.

As this article is not intended for the reading of people who have
given any particular attention to the facts at present known of the
way in which the mosquito carries disease from one person to another,
I think it best to briefly call attention to the leading points in our
present knowledge of this subject.

Malaria and yellow fever are the two great diseases with which the
mosquito is concerned. They are b}’ lar the most important diseases
in the tropical countries of the Western Hemisphere, and play a great
part in the sickness of the southern part of the United states. Up
to twenty-five years ago it was universally believed that malaria
was caused by a gas, or miasm, arising from the decomposition of
dead vegetable matter in hot countries, but about that time a French
army surgeon in Algeria, Laveran by name, noticed that if he looked
sufiiciently carefully with his microscope, in the blood of persons suf-
fering from malaria, he could almost always find a very small animal
parasite. This little, living being got into the blood in some way,
Laveran did not know how, fed upon the red blood corpuscles, and
was apparently the cause of the disease which we call malaria. Lav-
eran’s discovery was a great advance in our knowledge of the disease,
and it was gradually accepted by all the medical world.

A careful search was made for the parasite by many investigators,
but it could only be found in the blood of human beings suffering from
malaria. Where else it was bred and how it got into the blood of
man no one could find out. About this time it was discovered by an
English army surgeon. Doctor Manson, that a small worm — the Filaria
sanguinis homi/nis — was introduced into the body by the bite of a mos-
quito. (This worm causes the disease among human beings known as
nlariasis, and to it are due the enormous and unsightly swellings of
the legs and other parts of the body seen by our people in Cuba and
the Philippines. It is, however^ a disease very rarely found in the
United States, and not of much importance to us. I only mention it
here in connection with my story of the mosquito.)

About fifteen years after the discovery of Laveran, that malaria
was due to an insect in the blood, and of Manson, that a certain worm
which caused disease was introduced into the human blood by the bite
of a mosquito, another great English army surgeon, Ronald Ross,
discovered that the malarial parasite was found in a certain species of
mosquito — the anopheles — after the insect had bitten a human being
suffering from malaria. With his miscroscope he followed the Life
history of this parasite, from the stomach of the mosquito, through
the walls of the stomach into the mosquito’s body, and finally into its

3

4 DIEECTIONS WITH REGAKD TO DESTROYING MOSQUITOES.

salivary dands. In the saliva of the mosquito, the little organism
was found in large numbers, and when biting man, for the purpose of
getting blood, the mosquito injects her fatal saliva, just as does the
rattlesnake when he bites. This discovery of Doctor Ross was demon-
strated in the most positive manner.

An Italian, living near Rome, in Italy (malaria is very bad in the
neighborhood of Rome), while suffering from a malarial attack, was
bitten by an anopheles mosquito. This mosquito was then taken to
London, England, where they have no malaria, and a healthy young
man, who had never had malaria, was bitten by her. In a few days the
young man had a well-marked attack of malaria, with the usual symp-
toms, and the malarial parasite was seen by the microscope circulating
in the blood of the patient and feeding upon the red blood corpuscles
of his blood. And, again, men were taken, put into houses, screened
so that mosquitoes could not get in, and spent weeks in this unhealthy
part of Italy without getting sick. Yet this particular part of Italy
is considered so unhealthy that during the summer season neither
native nor foreigner, who can avoid it, spends a night there.

A night spent in the Campania used to be thought a certain way to
contract malaria; the idea being that the foul air from the marshes
caused the disease. Yet it is now seen that entirely unacclimated men
can breathe this air with safety, provided only that they live in'screened
houses and are not bitten by mosquitoes. These and similar facts con-
vinced the scientific world that the malarial organism gets into the
blood of the human being through the bite of the anopheles mosquito,
and in no other way.

Before the year 1900 it was universally believed that yellow fever
was carried from person to person and spread generally by a germ,
which up to that time had not been discovered. The germ was sup-
posed to travel from person to person by contact with those sick of the
disease, or by means of clothing or other articles which had been near
the sick, and its development was believed to be greatly favored by all
conditions which increased filth. There were a good many facts in the
spread of the disease which were difficult to account for under this sup-
position, but nevertheless it was the best explanation possible, and,
as I said, was almost universally accepted, both by physicians and people
generally.

During the year 1900 the Army of the United States had entire
control of Habana, at that time the great center of yellow fever for
the world. An excellent opportunity for investigating the disease
therefore existed. The Surgeon-General of the Army sent to Habana
a board of army medical ofificers for the purpose of investigating yellow
fever. This board was made up of the following army doctors: Doctor
Reed, the president, and Doctors Carroll, Agramonte, and Lazear.
After much investigation they determined to study the relation of tlie
mosquito to yellow fever. Their attention was called to this matter
by the part that the mosquito had already been proved to play in
malaria and filariasis, as mentioned above, and also by certain facts
known in the history of yellow fever epidemics. Doctor Finlay, a
prominent physician of Habana, reasoning from certain peculiarities
of yellow fever and from experiments which he made, had maintained
for many j^ears that a certain kind of mosquito in Habana, the stego-
myia^ was the cause of yellow fever, but he had not been able to
prove it.

DlHECTlONS WITH EEQAED TO DE8TEOYING MOSQUITOES. 5

The army board of which Doctor Reed was president recognized
that in Cuba, where they did their work, it would have to be entirely
evident that the men experimented upon could not get yellow fever
accidentally in Habana, or anywhere else, but only, if at all, in the
course of the experiment. They therefore took a piece of unoccupied
ground about six miles from Habana and built there a camp of material
which could not have been infected with yellow fever. They then got
men who had never sulfered from yellow fever and placed them in
these tents. It was known that if a man exposed to yellow fever were
going to have it the disease would develop in less than six days, and
if he passed through six days safe and sound he was known to have
escaped that particular exposure.

The board therefore argued that if they kept their men in this camp
for a period of two weeks they would be safe from any exposure
which might have occurred before their coming to the camp. They
also had to provide means which would insure their men not leaving
the camp, contracting the disease outside, and thus bringing infection
into the camp. This was done by a military guard, who allowed no
one to go out or come in without Doctor Reed’s permission. Things
were now so arranged that if a mosquito was allowed to bite a man,
and yellow fever developed, the board could l)e certain that the yellow
fever was due to the bite of the mosquito alone. They did a great
deal of experimenting here before they worked out all the details of
the way in which the mosquito actually conveys yellow fever. They
finally found out that if a female mosquito of one particular species,
the stegomyia, was applied to a yellow-fever patient in the first three
days of his sickness, and then kept from ten to twenty days and
allowed to bite a human being who had never had yellow fever, he
would very generally develop the disease within six da}'^s after the bite.

They also found out that this same man, before he had been bitten by
the yellow-fever mosquito, could sleep in the bed in which a patient
had died of yellow fever, could be covered with a black vomit from a
yellow-fever patient, or be exposed to the emanations from yellow
fever in any other way, and as long as he was kept safe from the bite
of the mosquito he would not have yellow fever; but this same man,
after all this exposure, if afterwards bitten by an infected yellow-fever
mosquito, would very certainly catch the disease. I think it would be
interesting to give some of the details of the work by which this great
discovery was demonstrated.

They had a little frame building built in this camp furnished with jars
and the necessary simple material for breeding mosquitoes. The build-
ing was carefull}’ screened and guarded, so that mosquitoes could not
get in nor out. Eggs of this particular species of mosquito were
obtained and hatched in one of the jars. A female mosquito was taken
from the brood thus hatched. The male mosquito will not bite, and
can readily be distinguished from the female with a magnifying glass
by the fact that the male has very heavy feathery feelers (antennae)
growing from his head. The female mosquito selected was put into a
small glass tube, stoppered with a little cotton, so that she could get
air freely but not escape, taken to Habana, placed on the hand of a
patient in the fii'st thi'ee days of an attack of yellow fever, and allowed
to fill herself with blood. She was then brought back to her former
home, placed in a large glass jar, and allowed to digest the blood she
had obtained. The jar, covered with a piece of mosquito netting, had

6 DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES.

in it a small saucer with a little water, and a lump of white sugar was
also provided. Under these conditions the mosquito was furnished
with all the necessities of life.

So confident were the men in charge of the mosquitoes that I have
known them to put their hands in the jars and let the mosquitoes feed
upon theui, up to the fifth or sixth day after the mosquito had bitten
a yellow-fever patient. The mosquito, you recollect, can not convey
the disease till from twelve to twenty days have passed from the time
of her biting the yellow-fever case from which she becomes infected.

On the other hand, I once saw a party of twelve or fifteen doctors
in the mosquito room one day, when the mosquito-bar covering of the
jar accidentally came oft' and the insects escaped into the room. These
doctors had come from other countries to investigate the subject, and
were not then convinced that the mosquito carried yellow fever. Still,
they did not care to put the matter to a practical test in their own per-
sons, and got out of the room so rapidly that the wire-screen door was
broken down during their exit. It happened that the mosquitoes in
this jar had never bitten a yellow-fever patient and were not infected.

After the mosquito had been left in this condition for from ten to
twenty da}'^s, it was known that her saliva was capable of transmitting
the disease. When she was wanted for the purpose of giving some-
body yellow fever, a man would take a glass tube, slip his hand under
the mosquito netting, put the mouth of the tube over the mosquito,
and then fill the mouth of the tube with a cotton stopper, as above
described. She would then be taken to the man to whom it was desired
to give yellow fever and who had bravely volunteered for the purpose,
the cotton stopper taken out, the tube turned upside down with its
mouth resting on the skin, and the mosquito allowed to settle. She
would then introduce her biting apparatus and slowly fill herself with
blood. But before she fills with blood she injects her saliva into the
wound, just as does the snake in biting. It is this injection of the
saliva that causes the swelling and the burning sensation that is felt at
the point where the mosquito bites and which lasts some time after
she has finished. The injection of the irritating saliva probably has
the effect of making it easier for the mosquito to get blood.

Now, it will be remembered that this man who was bitten had been
kept in the camp for two weeks before he was bitten, and isolated in
such a way that he could not possibly have contracted }^ellow fever.
There were thirty or forty men in the same camp under exactly the
same conditions. Three or four days after he was bitten by the
mosquito he developed a well-marked case of yellew fever, although
everybody else in the camp remained well. Doctor Reed and his
fellow-workers, therefore, very naturally believed that that particular
mosquito gave the man yellow fever. They repeated this test twelve
or fifteen different times with the same result. Nobody else in the
camp had yellow fever. Always within six days after the bite of the
mosquito known to be infected, the man experimented upon had }^el-
low fever.

To show how a house could become infected with yellow fever, the
board conducted the following experiment: They built a large room
and screened it so that mosquitoes could not get in or out. (mienever
I use the word “screen” here I mean the ordinary wire netting or
mosquito bar.) The purpose is of course to leave a perfectly free cir-
culation of air, but to have the meshes of the wire or mosquito bar

DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES. 7

netting so small that a mosquito can not get through. They then
divided this room into two parts by a wire netting extending from top
to bottom, so that a mosquito could not pass from one side to the other,
but at the same time leaving the circulation of air entirely free, the
desire being to show that if it were any miasm, or emanation, or germ
floating in the air which caused yellow fever it could freely pass from
one side to the other of this netting, and that both rooms, as far as
these emanations were concerned, were in the same condition.

Now, to show that the building was uninfected, four men were put
in it who had never had yellow fever, two sleeping on each side of the
wire netting. They were left there for two weeks and remained per-
fectly well. Reed then said, “I am now going to infect the room on
one side of this wire netting with yellow fever and not infect the other
side.” He took the two men out of oue side and liberated a half dozen
infected female stegomyia mosquitoes on this side. The two men still
slept and lived on the uninfected side. He then put a volunteer on
the side with the mosquitoes and left him there for half an hour, took
him out, and within six days this man developed yellow fever, the two
men on the other side of the room remaining well.

He therefore argued that, as the two men who had been for so long
a time on one side of the wire netting and remained well were
• breathing the same emanations, and the only ditterence was that there
were mosquitoes on the infected side to which the man had been
exposed for half an hour, it was very good proof that the mosquito
was the factor which gave yellow fever. He then said, “Now that 1
have shown you a house infected with yellow fever, I will demonstrate
how it can be disinfected and rendered safe.” He then caught his
half dozen mosquitoes, bottled them up and put them back into their
jars, and announced that the building was entirel}’^ safe and uninfected,
put the two men back into the side which had been infected, and the
four continued to sleep and live as safely in these quarters as they had
before the infection.

The board had another room built and got all sorts of material
infected by yellow-fever patients from the hospital, clothing worn by
patients at the time the}' died of yellow fever, such as mattresses on
which they died, soiled in every possible way, pillows and pillowcases
saturated with black vomit, and blankets over which basi ns of black vomit
had been poured; in short, material infected by yellow fever in every
possible way that could be thought of. All this material was placed in
the room, which was made close and tight with very little ventilation, so
as to make the conditions most favorable for what was ordinarily con-
sidered the best way of insuring the spread of yellow fever. Volunteers
who had never had }^ellow fever were placed in this room, lived and
slept there for two weeks at a time, wore this clothing, slept on these
mattresses, under these sheets, and yet not a single case of yellow fever
was developed from this contact. The men who had undergone this
exposure were taken out and kept for two weeks so as to insure that
they had not contracted yellow fever from the exposure, and then
bitten by infected mosquitoes. The}' always got yellow fever from
the bite of the mosquito, but never in any other way.

At this time the military authorities had had* entire control of
Habana for about two years. An army doctor had been placed in
charge of the health department and given the means and power to
do wnat he thought most likely to free the city from yellow fever.

8 DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES.

Yellow fever in Habana was a disease like consumption in Galveston
or New Orleans— always there, and always one of the principal causes
of death in the city. And this had been the state of affairs as long as
anything had been known with any accuracy, either about yellow
fever or about the health conditions of Habana; and these things
were pretty accurately known for more than a hundred years imme-
diately preceding the time I refer to. When we organized our health
department,^ we believed, as did everybody else, that yellow fever was
caused by filth, dirt, and general insanitary conditions, so we went
to work doing our very best to correct these conditions. With these
efforts Habana very rapidly became a healthy city, as much so as
many of our large cities in the United States, but yellow fever did not
seem to be affected.

The second }mar of our control yellow fever was very severe in
Habana, but did not attack the native Cuban because he was generally
acclimated. Only the foreigner, therefore, was subject to the disease.
During the year 1900 many of our prominent American civilians
and military officials died of the disease, and the very cleanest and
best parts of the city and the people who lived best and took the best
care of themselves were most affected. When the army board pub-
lished their discovery to the world the health department of Habana
recognized that it and all the rest of the world had been on the wrong
track with regard to yellow fever, and they determined to change
their methods and attack the mosquito as the cause of the disease.

They had been convinced by the work of the army board that a
human being could only get yellow fever by being bitten by a particu-
lar kind of mosquito — the stegomyia — which had previously bitten a
man suffering from yellow fever. They therefore arranged that as
soon as a man sickened with yellow fever, employees from the depart-
ment went to the house and screened it with wire netting, so that those
mosquitoes that were in the house could not get out and those outside
could not get in. A smudge was then made of sulphur, tobacco, or
insect powder, as best suited to the circumstances, in the affected house,
and in all those immediately around it, with the intention of killing all
mosquitoes present. By this method it was hoped that both the mos
quitoes that nad bitten the man and caused the disease would be killed,
and also those that had bitten the man after he was taken sick, and
had thus become themselves infected and able to spread the disease.
For the purpose of doing this screening a building was arranged very
much like a fire station in one of our cities, where wagons, wire screens,
carpenters, and men with material for making a smudge, were always
kept on duty, who proceeded at once to the place where a yellow fever
case was reported to exist.

This method was very successful in its results. After its adoption
very few cases occurred where the disease spread from the person
infected to others in the neighborhood. It was also determined to
destroy as many as possible of the yellow fever mosquitoes in the city.
It was known that the female mosquito had to have water on which to
lay her eggs, and that these eg'gs could not hatch without water; that
this water had to be very quiet and well protected for the hatching
process to take place; that the eggs took about three days to hatch;
that after hatching the insect had to live the life of a fish in this water
for five or six days. During this fish stage they are known as larvas,
and are well known to everybody in the South, for they are nothing

I

DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES. 9

but the common wigglers always found in standing rain water during
the summer months. Now, while in this wiggler stage the insect has
to have air, and for this purpose must every little while come to the sur
face. At the end of five or six days the wiggler changes into the full-
grown mosquito.

It is known that this particular species of mosquito — the stegomyia,
or the yellow fever mosquito — lives and breeds almost altogether in
houses and in their immediate neighborhood, and does not leave the
house for any great distance. With this knowledge of its life history,
the department found it easiest to destroy the mosquito in its wiggler
stage, and the most useful means in this direction they found to be
the doing away with all the little deposits of water in and near inhab-
ited houses, which the wiggler must have in order to develop into the
mosquito. The methods Iierein described were not settled upon, as
might appear from this account, all at once and at the beginning, but
many other methods of waging war against the mosquito were tried,
found impracticable, and dropped.

With the object of doing away with the breeding places of the yel-
low fever wiggler all the houses and yards of Habana were carefully
examined and all tin cans, empty bottles, and trash of the same kind,
which were generally found filled with rain water, and full of yellow
fever mosquito larvae were carefull}' carted off. Then the necessary
openings in all cisterns were covered with mosquito netting, so that
the mosquitoes could not get in to lay their eggs. Among the poorer
people, who had only barrels and other similar receptacles for rain
water (and in Habana every family had something of this kind), the
health department arranged these necessary receptacles for them by
placing a wooden cover on the barrel, leaving a hole in the center of
this cover for the entrance of water, and covering the hole with wire
netting, so that mosquitoes could not get in. To enable them to draw
off the water without opening the barrel a cheap wooden spigot was
pi iced in the lower part.

Now from the peculiarity of the wiggler, that he has to come to the
surface of the water every few seconds to get air, if we put anything
on the surface of the water that prevents him getting this air, he
drowns just as certainly as a man would who is kept under the water.
Ordinary kerosene oil, a tablespoonful or two to a cistern, spreads
over the surface of the water and kills the wiggler in this way. He
can not break through the scum of oil to get air. But oil very rapidly
evaporates and has frequently to be renewed. So oil was only used
in Habana where no other method was successful. The privy pits in
all the houses there were in the center of the court, covered generally
with heavy flagstone. These pits not being in general accessible to the
inspectors had to be treated with oil. Once a month, a couple of
ounces of oil were poured into the pipes leading to the pits.

To insure that these methods and ordinances were carried out, the
city was divided into districts of about a thousand houses each, so
that an inspector would get over each district in the course of a month,
insi3ccting at the rate of about thirty houses a day. This inspector
had with him two men who used the oil as above described. He had
with him printed blanks on which he entered the condition of tlie
premises as to wigglers. These reports were turned in every night
to the office of the health department and were consolidated from da^'
to day. At the end of the month we could therefore tell the condition

10 DIEECTION'S WITH REGARD TO DESTROYING MOSQUITOES-

of Habana as to wigglers. At the first report on this subject (I think
in March, 1901), we found that we had in Habana in the neighborhood
of 26,000 different water deposits which contained wigglers, most of
them of the yellow-fever variety.

After once going over the city and carefully explaining to the peo-
ple the dangers of allowing wigglers on their premises, and after hav-
ing fixed up for the poor all the water barrels which they were
obliged to keep for holding their rain water, the mayor of the city
issued an ordinance stating that anybody who bred wigglers on his
premises would be fined $10. These two methods of destroying yel-
low fever mosquitoes, namely, that of killing the grown mosquito in
the neighborhood of every yellow-fever patient with a smudge and of
looking after the wigglers in all rain water deposits about the house,
were steadily enforced during the year 1901. The results were better
than we had dared to hope. Few cases occurred in which yellow fever
spread from a case cared for in this way. Yellow fever rapidly
decreased, and on September 28, 1901, the last case of yellow fever
occurred in Habana, and since that time — now more than two years —
not a single new case has developed in the city.

There were still, of course, a great many yellow-fever mosquitoes
in Habana, but these methods of destroying the wigglers had great 1}’^
decreased the numbers of mosquitoes. The report of January, 1902,
after about ten months of this mosquito tvork, showed that within the
city limits less than 300 premises had wigglers upon them. This I
think a very fair measure of the results accomplished by one year’s
work, namely, that the number of deposits containing wigglers had been
decreased from about 26,000 to about 300.

I think it is evident that the disappearance of yellow fever from
Habana was due solely to this mosquito work. Remember that it was
an every-day disease in Habana, and had been so for more than a hun-
dred years, just as consumption is in New Orleans, a city of about the
same size as Habana. Now, if some method should be adopted against
consiimption in New Orleans, and S3'^stematically put in operation in
the city against that disease, and at the end of a year it could be shown
that no new cases of consumption were occurring in New Orleans, and
at the end of two ,years and a half it could be further shown that under
the continuance of the same measures the disease had entirely disap-
peared from the city, and no new cases had occurred, I should think
that we would all be at once convinced that the disappearance of con-
sumption from New Orleans was due to the efficac}'^ of the measui'es
adopted.

In Habana, even now, a case or two of yellow fever comes in eveiy
month from Mexico and other infected regions which have a consider-
able trade with Habana. The ships are carefull}’’ inspected by the
quarantine authorities, just as is done in our country. If a person sick
of yellow fever, or suspected yellow fever, is discovered, he is landed
at the city wharf, in the heart of the business district, placed in an
ambulance, carried to the yellow-fever hospital, which is Avell within
the city limits, and treated there. The only precaution taken is to see
that Habana mosquitoes do not get an opportunity to bite him. The
authorities at Habana thoroughly believe that if tlic}'^ can prevent
mosquitoes from biting a yellow-fever patient the city will be entirel}’^
safe in handling him and taking care of him.

DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES. 11

In 1901, during the height of the yellow-fever work at Habana, a
town of about 5,000 inhabitants, some 12 miles from the city, became
badly infected with yellow fever. This town, Santiago de las Vegas,
was practically a suburb of Habana, and the business communication
with the city was very intimate. We found that people who were
working at Santiago de las Vegas were constantly getting sick of
vcllow fever, and as soon as the^'^ found themselves sick would come
into Habana to the homes of their friends and relatives to be taken care
of. In order to do away with this source of danger a large force of
men was put at work at Has Vegas, on the lines above described. The
whole town was systematically gone through from house to house, and
at the end of about six weeks of this work the disease was entirely
wiped out and we had no more trouble with infection from Las Vegas.
1 mention this as showing the po.ssibility of taking a small town and
getting rid of the disease rapidly by mosquito work.

We nad other mosquito work going on in the suburbs of Habana,
among the truck gardens and irrigated fields where grass was grown.
But the yellow-fever mosquito does not breed to any great extent in
such places, and I do not think this work had much efl'ect upon the
yellow fever. But malaria, as I have above mentioned, is also carried
exclusively b}’ a mosquito named the “ anopheles.” Now, this malarial
mosquito likes to breed in places where there are little puddles of
water, cow tracks, horse tracks, and similar depressions in grassy
ground, and the work in the suburbs had its principal effect upon this
mosquito. It was not desirable to stop irrigation, as the livelihood of
all these small farmers depended upon it, but by taking advantage of
the fact that a deposit of water had to remain undisturbed at least ten
days to breed a mosquito, we could allow them to irrigate freely, pro-
vided the water did not remain longer than a week. The health aepart-
ment had all this area arranged with shallow, superficial ditches which
would not interfere with irrigation, but would allow rapid drainage when
the water was taken off. All pools and puddles which had no economic
use were kept drained, and aitches and streams kept clean of grass
and obstructions.

After once getting the country cleaned up at public expense, and
the matter explained to the farmer, he was fined in the same way as
the householder in the built-ui) portion of the cit}% if wigglers were
discovered on his premises. Vv hile I do not think that these measures
aided us particularly in yellow fever, they had a marked effect upon
malaria. In 1900, the year before the mosquito work commenced, we
had in Habana 325 deaths from malaria. During 1901, the year in
which mosquito work was commenced, we had 151 deaths from malaria.
In 1902, the second year of mosquito work. Dr. Carlos Finlay, the
health officer of Cuba, reports 77 deaths from malaria in Habana, and
up to the 1st of November in 1903, the third year of mosquito work.
Doctor Finlay reports 45 deaths from malaria.

This mosquito work of the Habana health department, I hold, demon-
strates the uracticability of eliminating in theTropics — the two diseases
malaria and yellow fever— and I believe if the attention of the people
at large in our own country were generally attracted to the danger of
transmitting di.sease b}' the mosquito, and the practicability of destroy-
ing them, we could very generally eliminate these two diseases from
our own country.

12 DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES.

And now to the reason for writing this article. I thought an account
of the relations of mosquitoes to disease, given in simple terms, read-
ily understood by those who are not doctors, might help people gener-
ally in making an attempt to get rid of mosquitoes, each man about
his own house. I will now proceed to make suggestions in this direc-
tion. And in order to make myself entirely clear will repeat a good
deal, and enlarge upon what I have already said.

The work of the army medical board of which Maj. Walter Reed
was president, showing that a particular species of mosquito was the
only means of transmitting yellow fever, is now pretty generally
accepted by all the scientihc world. Based upon this knowledge,
certain methods were adopted by the army medical officers in Habana,
Cuba, which resulted in eradicating yellow fever from that city.
During the fall of 1903 yellow fever was introduced from Mexico
and became quite widely spread through western Texas. It is thought
that a few general rules, based upon the knowledge acquired by the
army board and the experience of the army medical officers in Habana,
may be of use in assisting individuals and towns in freeing themselves
from infected mosquitoes during the present winter and coming spring.
Otherwise, it seems highly probable that yellow fever, at some point
in Texas, will again develop as the warm weather comes on. This
would come about from the fact that the infected mosquito can very
readily live through the winter in the latitude of Laredo.

As yellow fever can only be spread by a particular species of mos-
quito, it follows that if there are none of these mosquitoes about,
yellow fever can not spread. The danger in Texas is that the stegomyia
mosquitoes, that have bitten people with yellow fever, will live through
the winter and spread another epidemic as the warm weather comes
on by biting people who have not had the disease. This mosquito,
from its nature, stays immediately about the house and in the rooms,
and seldom or never wanders far. It was found in Habana that by
destroying all the mosquitoes in each house where yellow fever
occurred the disease was always stopped in that particular neighborhood.
It is probable, therefore, that if each householder in whose house yel-
low fever has occurred during the past fall will destroy all the mos-
quitoes in his house he will be free from the old infection next spring.
This can 'readily be done by closing the room and making a smudge in
it of sulphur or tobacco. Care should be taken to paste all the cracks
up with paper, so that the smudge will be confined to the room fumi-
gated, and the pan in which the smudge is made placed on a little
earth, so that it can not set the floor on fire.

With sulphur, about a pound to a room 10 feet square should be
used, and with tobacco, about half a pound. To start the sulphur
burning a couple of tablespoonfuls of alcohol should be poured on
before applying the match. Sulphur should be used unless the I’ooni
contains valuable material which might be injured by it. The fumes
of tobacco hurt nothing, but leave a disagreeable odor. The fumes
of ordinary Persian insect powder hurt nothing and leave no odor, but
it does not always kill the mosquitoes and care has to be taken to sweep
them up afterwards. A couple of hours will be time enough to keep
the room closed. After that time it can be opened, aired, and occu-
pied. In towns, this method should be carefully carried out during
the winter by the town authorities. Not only the houses in which
yellow fever is known to have occurred, but every house in the infected

DIRECTIONS WITH REGARD TO DESTROYING MOSQUITOES. 13

town should be treated in this way. W e found in Habana that a squad
of five men, under intelligent direction, could easily fumigate a 10-
room house in two hours. It should be arranged so that the whole of
the infected town should be gone over before the 1st of April.

The above directions cover the points with regard to killing infected
mosquitoes, and thereby preventing the liability of a new epidemic
next summer from the old mosquitoes left over from last year. But
it is even more important to prevent the breeding of a new crop of
Ktegomyia mosquitoes, and this can be very readily done without very
great effort.

The female stegomyia mosquito always seeks some small body of
well protected fresh water in which to lay her eggs. On the surface
of this water she lays about 60 or 70 eggs. These, in warm weather,
• in three days hatch out into the ordinary wiggler, and the wiggler in
five or six days develops into the full-grown mosquito. From the
laying of the egg to the development of the full-grown mosquito takes
about eight days in hot weather. Water is as necessary to the insect
as it is to a fish. It is essentially a water insect during this period,
though it is an air-breathing insect too, and has to come to the surface
of the water every few seconds to get air.

As I stated above, the stegomyia seeks particularly deposits of clean
water, and is essentially a house mosquito, breeding either in the
house or very close to it, in such places as cisterns and rain-water bar-
rels, and in anything likely to catch and retain rain water, such as old
bottles or cans, or gutters under the roofs of houses, etc. Now, if
every householder will give a little attention to see that there are no
such deposits about his house, he will be free from the stegomyia mos-
quito, and no one will contract yellow fever in his house, even if cases
are introduced into it from elsewhere. If necessity obliges him to
keep a cistern or barrels of rain water, if he will arrange the receptacle
so tliat the mosquito can not get in to lay her eggs, it will be entirely
safe. In the cistern this can be done by covering the top tightly, with
the exception of a hole for ventilation, and one for the entrance of the
water, and these two holes should be covered with wire netting. The
netting should be not larger than 16 meshes to the inch. A larger
mesh than this will allow the smaller size of stegomyia to pass through.

Water barrels can be ari'anged in the same way, a tight-fitting top
put on, with a wire mesh over the hole for the entrance of the water,
and a cheap spigot put in the bottom for drawing off water. If he
finds wigglers in any of the vessels of water which he is obliged to
keep, he can know that his cover is imperfect, and that the female
mosquito has gotten in there in some way to lay her eggs. Small
deposits about the yard and in the immediate neighborhood should be
swept out or drained awa}'. A deposit of water in Texas would have
to stand at least ten days to breed a mosquito. For this reason, if the
householder is not able to arrange his water vessels as above suggested
he could avoid breeding stegomyia mosquitoes by having these vessels
emptied once a week. But if the method of emptying is used, the
larvae should be carefully washed out or the vessel left to stand empty
for more than an hour. If this precaution is not taken, a considerable
number of the larvae will be left adherent to the bottom and sides and
will live if the vessel is at once refilled. Kerosene oil is fatal to the
larvae if two or three tablespoonfuls are spread over the surface of
the water.

14 DIKEOTIOJSI8 WITH EEGARD TO DESTROYING MOSQUITOES.

As I said before, the larvae have to come to the surface everv few
seconds to get air, and as they are unable to break through the film
of oil they die of suffocation, but the oil evaporates very rapidlv and
should be renewed every week. Much the better method is either to
get rid of the deposit of water or protect it in the above-mentioned
manner. Oil should only be relied upon in treating deposits in a
building or its immediate neighborhood which can not be managed in
one of the above-mentioned methods. Privy pits which contain water
were the only places in Habana in which we habitually resorted to

^ In towns these methods should be enforced by regular and systematic
inspections. In most towns there are ordinances against pigs and piff-
sties. A hog IS considerably larger than a mosquito wiggler, but with
a little care an inspector will soon learn to discover the wigglers almost
as easily as the hogs. And the householder should be taught that the
wiggler causes a great deal more annoyance to himself and his neigh-
bors than the hog does, and is infinitely more dangerous to health.
And the ordinances should hold the householder as strictly to account
for breeding wigglers on his premises as for having a pigsty with a
litter of pigs. The larger deposits, a hundred yards or more away
from the house, such as small ponds and swampy places, while breed-
ing mosquitoes that cause a great deal of annoyance, will not breed
the steg’omyia to an extent sufficient to be dangerous to the house.
They should be manag'ed by the town authorities on the same general
principles— to drain wherever possible.

O

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