THE PREVENTION OF 
YELLOW FEVER. 
BY 
WALTER REED, M.D., 
SURGEON, U. S. A., 
AND 
JAMES CARROLL, M.D., 
CONTRACT SURGEON, U. S. A., 
Reprint from the Mbdxcal Record, 
October 26, 1901. 
WILLIAM WOOD AND COMPANY, 
NEW YORK. THE PREVENTION OF 
YELLOW FEVER. 
BY 
WALTER REED, M.D„ 
SURGEON, U. S. A., 
AND 
JAMES CARROLL, M.D., 
CONTRACT SURGEON, U. S. A. 
Reprint from the Medical Record, October 26, 1901. 
william wood and company, 
51 Fifth Avenue, New York. 
1901. THE PREVENTION OF YELLOW FEVER * 
By WALTER REED, M.D., 
SURGEON, U. S. A., 
AND 
JAMES CARROLL, M.D., 
CONTRACT SURGEON, U. S, A. 
The prevention of yellow fever since its first importa- 
tion into the United States in 1693, and especially 
during the latter half of the past century, has com- 
manded, perhaps, more attention on the part of those 
who were concerned with matters pertaining to the 
public health than the prevention of any of the other 
acute infections. This has not been occasioned by 
the fact that its total sickness and mortality have 
exceeded that of other acute infectious diseases, 
such as typhoid fever or croupous pneumonia, but 
because rather of the proximity of its source to our 
shores; the lack of knowledge of its specific agent; 
the consequent mystery surrounding its origin and 
propagation; the alarmingly rapid spread and course 
of this disease, when once it had obtained a foothold, 
and the high mortality with which its epidemics have 
generally been attended. Although the duration of 
ts presence in our seaports was plainly limited by 
icertain seasonal conditions, yet during its brief reign 
-July to October-its ravages were such as to com- 
pletely paralyze both the social and commercial in- 
terests of a given city, and even of an entire section 
of our country. 
*Read at the twenty-ninth annual meeting of the 
American Public Health Association, held in Buffalo, 
N. Y., September 16-21, 1901. 
Copyright, William Wood and Qompany 
3 The interval between 1793 and 1888 is almost one 
hundred years, but upon the appearance of yellow 
fever we observe no difference of behavior on the 
part of the inhabitants of Jackson, Miss., in 1888, 
from that shown by the citizens of Philadelphia in 
1793, except that the terror of the former was greater 
and their flight from their homes more precipitate 
than in the case of the latter. 
The recurrence of succeeding epidemics has, there- 
fore, served to increase rather than to lessen the 
public alarm. 
It would be difficult to determine with accuracy 
the loss of life occasioned by the ninety-five invasions 
of our territory by yellow fever during the past two 
hundred and eight years. We have endeavored to 
collect from the most available sources the mortality 
caused by this disease, but have been unable to obtain 
any reliable data for the earlier epidemics. If we 
confine ourselves to the epidemics which have oc- 
curred since 1793, we find that there have not been 
less than 100,000 deaths from this cause. The great- 
est sufferer has been the city of New Orleans, with 
41,348 deaths, followed by the city of Philadelphia 
with 10,038 deaths. The epidemics of 1855, 1873, 
1878, and 1879 claimed 7,759 victims in the city of 
Memphis, Tenn. From 1800 to 1876, Charleston lost 
4,565 of its citizens by attacks of yellow fever. New 
York, during the earlier and later invasions of this 
disease, has had 3,454 deaths, while the epidemic of 
1855 in Norfolk, Va., caused over 2,000 deaths. Dur- 
ing our brief occupation of the Island of Cuba (July, 
1898-December, 1900), with every precaution brought 
into exercise to ward off the disease, there have oc- 
curred among the officers and men of our army, 1,575 
cases of yellow fever with 231 deaths. 
If we reckon the average mortality at 20 per cent., 
there have not been less than 500,000 cases of yellow 
4 fever in the United States during the period from 1793 
to 1900. 
Turning for a moment to other countries, we find 
that the great epidemic of 1800, in the province of 
Andalusia, Spain, caused 60,000 deaths, and that 
20,000 more deaths attended the invasion of the city 
of Barcelona by this disease in 1821. From 1851 to 
1883, 'the deaths from this cause in the city of Rio de 
Janeiro were 23,338, while in the city of Havana, 
between the years 1853 and 1900, 35,952 deaths 
have been recorded from yellow fever. 
We have no means of computing the damage done 
to the commercial interests of the United States by 
epidemics of yellow fever. At the sixth annual 
meeting of this association, held in Richmond, Va., 
in 1878, Dr. Samuel Choppin, President of the State 
Board of Health of Louisiana, estimated the actual 
cost of the epidemic of that year to the material 
resources of the city of New Orleans as $10,752,500. 
Dr. Benjamin Lee, the present distinguished occu- 
pant of the presidential chair, at the seventeenth 
annual meeting of this association, held in Brooklyn, 
N. Y., in 1889, contributed a paper having the title, 
" Do the Sanitary Interests of the United States 
Demand the Annexation of Cuba?" From this we 
quote the following sentence: ''A single widespread 
epidemic of yellow fever would cost the United 
States more in money, to say nothing of the grief 
and misery which it would entail, than the purchase 
money of Cuba." That this was no exaggeration, 
witness the language of the petition which the chair- 
man of the committee on the etiology of yellow 
fever, in conjunction with other prominent members 
of this association, presented to the President of 
the United States on November 15, 1897, and again, 
on November 21, 1898, in accordance with a reso- 
lution adopted at the meeting of this association, 
held at Ottawa, Canada, in 1897. In addressing 
5 President McKinley, Dr. Horlbeck said: "It is 
hardly necessary to call your attention to the seri- 
ous results of the recent epidemic of yellow fever 
in the States of Louisiana, Mississippi, and Alabama, 
but we may be permitted to mention the fact that 
the great epidemic of 1878 resulted in the loss of 
nearly 16,000 lives, and that it has been estimated 
that the total loss to the country resulting from this 
epidemic was not less than $100,000,000." 
The importance of the study of the causative 
factors entering into the propagation of a disease 
so capable of quickly destroying the lives of the 
citizens and wrecking the commercial interests of 
the cities of the United States could hardly be over- 
estimated. Did time permit, we would be glad to 
refer to the numerous and valuable contributions 
made to this subject by the members of the Ameri- 
can Public Health Association. We can only men- 
tion the establishment of the National Board of 
Health and the appointment of the Havana Yellow 
Fever Commission of 1879 as two of the most im- 
portant outcomes of the persistent efforts of this 
association, following " the deeply tragical events 
of the summer of 1878." The exhaustive reports 
made by Chaille in 1880, and by Sternberg in 1890, 
must always stand as monuments to the earnest 
spirit of investigation with which the work was 
pursued. 
Notwithstanding the importance of the work and 
the efforts put forth by students in this and other 
countries, we believe that we are safe in saying that 
no results had been obtained which would enable 
us to combat successfully this disease when once 
imported into our larger centers of population, and 
no means found to keep it out of our ports except 
such as would place very heavy burdens upon com- 
merce. This inability to control the disease grew 
not only out of our ignorance as to the way or ways 
6 in which yellow fever was propagated, but also out 
of certain false opinions which we had formed as to 
the mode of its spread. The doctrine of the spread 
of yellow fever by fomites and by filth had taken 
such hold on the professional mind as completely to 
overshadow all other views, and to direct into false 
channels the work of those who were engaged in 
the investigation of this disease. The efforts to 
isolate or to discover the specific agent of yellow 
fever, if successful, would possibly have greatly 
simplified the problem; in the absence of such dis- 
Fig. i.-Stegomyia Fasciata; Female, a, Front tarsal claw. 
7 covery, the first step in our knowledge of how to 
prevent this disease could only be found, we think, 
along another line, viz., that of its propagation from 
the sick to the well. This step we endeavored to 
take, in connection with our colleagues, Dr. Agra- 
monte and the late Dr. J. W. Lazear of the United 
States Army, during our recent investigations into 
the causation and spread of yellow fever at Que- 
mados, Cuba. 
The results of our earlier work relative to the 
etiology and propagation of this disease we had the 
pleasure of presenting to this association at its last 
meeting, held in Indianapolis, Ind.1 You will recall 
that one of the conclusions which we then submitted 
was as follows: " The mosquito serves as the inter- 
mediate host for the parasite of yellow fever." In 
the same article, we briefly indicated the reasons wreich 
influenced us in pursuing this line of investigation, 
and it is, therefore, unnecessary here to repeat them. 
Continuing our studies, especially as regards the 
means by which yellow fever is spread from individ- 
ual to individual, and as to the manner in which 
houses become infected, we were able, under strict 
rules of isolation and quarantine, to bring about an 
attack of yellow fever in ten non-immune individ- 
uals (and always within the period of incubation of 
this disease) out of a total of thirteen (76.84 per 
cent.) whom we attempted to infect by means of 
the bites of mosquitos-stegomyia jasciata-that had 
previously been fed with the blood of yellow-fever 
patients during the first, second, and third days of 
their attacks. These results were reported in part 
to the Pan-American Congress held in Havana dur- 
ing February of this year,2 and in part to the Asso- 
1"The Etiology of Yellow Fever-A Preliminary Note." 
-Philadelphia Medical Journal, October 27, 1900. 
2"TheEtiology of Yellow Fever-An Additional Note," 
Journal American Medical Association, February 16, 1901. 
8 ciation of American Physicians at its last meeting 
held in the city of Washington.3 
It will be seen that we were able to establish in 
the most conclusive manner that the mosquito does 
Fig. a.-Stegomyia Fasciata; Male, a, Front tarsal claw. 
serve as the intermediate host for the parasite of 
yellow fever. At this same Experimental Sanitary 
Station we were, also, able to demonstrate that an 
attack of yellow fever cannot be induced by the 
3 " Experimental Yellow Fever," American Medicine, 
July, 1901. 
9 most intimate and prolonged contact with the cloth- 
ing and bedding of yellow-fever patients, even though 
these articles had been previously thoroughly and 
purposely soiled with the excreta of such patients. 
In other words, we were able to prove that the gar- 
ments worn, and the bedding used, by yellow-fever 
patients were no more concerned in propagating this 
disease than the clothing and bedding of patients 
suffering from malarial fever are concerned in the 
spread of the latter malady. The doctrine of the 
spread of yellow fever by fomites having, at the first 
touch of actual experiment on human beings, burst 
like a bubble, we may hereafter cast it aside, with 
other exploded beliefs, to the very great simplifica- 
tion of the problem how to prevent yellow fever. 
Indeed, in our opinion, the time has now arrived 
when the latter problem may be reduced to meas- 
ures which shall prevent the propagation of this 
disease by mosquitos. Although the specific agent 
of yellow fever has not, as yet, been discovered, 
this must remain largely a matter of scientific inter- 
est, and does not, in the least, lessen the efforts 
which we, as sanitarians, are now able, for the first 
time, to bring into action for the prevention of the 
spread of this disease, since, in dealing with the mos- 
quito, we are dealing with the intermediate host 
which carries the specific agent from the sick to the 
well. 
In considering, then, in a broad way, the preven- 
tion of yellow fever, the natural order would be to 
give our attention, first, to measures which will pre- 
vent the importation of this disease from infected 
places into the seaports of the United States; and, 
secondly, to measures which will most effectually 
prevent the spread of this disease, provided it should 
gain a lodgment in one of the cities of this country. 
With your permission, however, we will reverse 
the order of consideration above suggested, and will 
10 later refer in the briefest manner to the prevention 
of the importation of yellow fever into the United 
States from foreign ports, as this part of the subject 
will be presented by the Health Officer of the Port 
of New York, who, from long experience, will be able 
Fig. 3.-Stegomyia Fasciata. Batch of fifty-twd eggs as 
deposited by a single female. Slightly enlarged. 
to deal more intelligently than we with this part of 
the problem. 
Since the mosquito, especially that species of steg- 
omyia which has recently been designated by Theo- 
bald as slegomyia fasciata (formerly known to 
Fig. 4.-Stegomyia Fasciata. Forty-eight eggs deposited in a 
close-lying mass. Enlarged. 
entomologists as culex jasciatus-Fab.), has become so 
prominent a factor in the spread of yellow fever, it 
becomes necessary to consider this insect from the 
point of view of its identification; its habitat; its 
breeding places; the length of its generation; its hours 
11 of feeding; the influence of temperature upon both 
its propagation and stinging; the interval after con- 
tamination before the insect becomes capable of prop- 
agating the disease; the length of time during which 
it remains dangerous; the measures that should be 
used not only to protect the sick against the bites 
of these insects, but also to prevent the latter from 
infecting the healthy individual; and, finally, a con- 
sideration of the several agents which may be suc- 
cessfully employed both to prevent the breeding of 
mosquitos as well as directed toward their destruc- 
tion in the adult stage. 
Aside from the standpoint of scientific interest, it 
is certainly a matter of hygienic importance, in tak- 
ing up the question of how to prevent the spread of 
yellow fever, when imported into the United States, 
that the health authorities of our several coast cities, 
and, indeed, of some of our inland towns, should 
be able to determine whether the only species of mos- 
quito, which, up to the present time, has been shown 
capable of conveying yellow fever, is or is not present 
in these cities. If it should hereafter be proven that 
only species of the genus stegomyia are capaple of 
acting as intermediate hosts for the specific agent 
of yellow fever, as appears to have been demon- 
strated for the genus anopheles in the spread of 
malaria, the presence or absence of the former genus 
will definitely determine whether yellow fever will 
or will not spread in a given locality. The presence 
or absence of mosquitos that can propagate the 
disease is the only intelligible explanation of what 
has heretofore been considered an inexplicable prob- 
lem, viz., the capability of this disease to propagate 
itself in certain localities, while in other places it 
could be introduced with perfect impunity to the 
public health. In othei* words, our present knowl- 
edge of this question solves, at last, the problem 
of the portability or non-portability of yellow fever. 
12 Description of Mosquito.-The identification of 
stegomyia fascia.a-Theobald-should not be diffi- 
cult. This mosquito, when examined closely with 
the naked eye and especially with a pocket lens,, is 
a rather striking-looking and handsome insect. (Fig. 
1.) Its most conspicuous markings are the broad 
semi-lunar silvery stripe, which is seen on the lateral 
surface of the thorax, and the white stripes at the 
bases of the tarsal joints. These may be readily 
distinguished with the naked eye. The bands on 
the hind legs are especially well marked, and occa- 
sionally the entire fifth hind tarsal joint is seen to be 
Fig. 5.- Stegomyia Fasciata. Newly deposited egg. X 50. 
a, Empty shell from which larva has escaped. 
of a pure silvery white. The four stripes of silvery 
scales which are seen on the posterior surface of the 
thorax serve to distinguish this species from all other 
mosquitos, except stegomyia signifer-Coquillet- 
in which, however, as we have been informed by 
Mr. L. O. Howard, the curved thoracic band is very 
narrow and of a somewhat different shape. Exam- 
ined with a hand lens, the four stripes are seen to 
consist of two lateral, distinct silver lines-the con- 
tinuation of the semi-lunar, broad stripes-and two 
fine, white lines situated between these, and which 
13 require that the insect shall be held in the proper 
light, in order that these delicate threads may be 
distinctly seen. The lateral surface of the thorax 
is also marked by several silvery dots and the abdo- 
men by distinct white stripes. This description ap- 
plies to both sexes. In the female, the palpi are 
short, as in the genus culex. The proboscis is of a 
dark blackish-brown color and is destitute of a whit- 
ish band near the middle. In the male (Fig. 2), 
one of the front tarsal claws bears a tooth on the 
under side, while the other claw is destitute of such 
marking. In the female, both front tarsal claws 
bear a distinct tooth near the base of the under side 
of each. 
Habitat.-We have found this mosquito in all of 
the principal cities of Cuba, and have received speci- 
mens from a number of the smaller towns on this 
island. According to Howard1 it has been found 
at Kingston, Jamaica, on the Isle of Pines, and at 
Bluefields, Nicaragua. He also reports that Theo- 
bald has received specimens of this insect from Italy, 
Greece, Spain, Portugal, Gibraltar, and Malta. In 
the United States, Howard reports its presence at 
New Orleans, Natchitochez, and Napoleonville, La.; 
in Eastern Texas; Hot Springs, Arkansas; Pelham, 
Ga.; and from Virginia Beach, near Norfolk, Va. 
To this we can add Augusta, Ga., from which city 
we have recently received specimens of stegomyia 
fasciata through the courtesy of Dr. T. 0. Oertel of 
that city. Dr. Durham of the English commission 
for the study of yellow fever kindly showed us speci- 
mens of this insect which he had collected at Para, 
Brazil, and at various places along the Amazon 
River. It will be seen, therefore, that stegomyia 
fasciata has a wide distribution in the warmer coun- 
tries of the globe, and especially at low altitudes. 
1,1 Mosquitos," etc., by L. O. Howard, New York, 1901. 
14 A more exact knowledge of the distribution of this 
mosquito in the United States is, we think, a matter 
of considerable practical importance. 
Breedins. Places.-In our search for the larvae of 
Fig. 6.-Stegomyia Fasciata. Full-grown larva enlarged. 
this insect we have found them in the following 
places: (1) In rain-water barrels; (2) in sagging 
gutters containing rain water; (3) in tin cans that 
had been used for removing excreta and which still 
Fig. 7.--Stegomyia Fasciata. Pupa, enlarged. 
contained a small amount of fecal matter; (4) in 
cesspools; (5) in tin cans placed about table legs 
to prevent the inroads of red'ants; (6) in the 
15 collection of water at the base of the leaves of the 
agave americana', (7) in one end of a horse trough 
that was in daily use. It follows that stegomyia, 
like culex, will breed in any collection of still water, 
rain or hydrant, and that the presence of fecal 
matter does not seem objectionable. Indeed, we 
have been in the habit of adding a very small quan- 
tity of the latter to our breeding jars, as it has seemed 
to hasten the development of the larvee. In water, 
however, which contains much suspended soil- 
muddy water-the larvse, in our experience, do not 
flourish, but die off rather rapidly. 
Deposition of Eggs.-The insect lays her eggs dur- 
ing the night, and, unlike culex, which deposits its 
eggs in boatlike masses, stegomyia extrudes her eggs 
on the surface of the water in pairs, in groups of 
three or more, or singly; in this respect resembling 
anopheles (Fig. 3). Exceptionally, the eggs are 
deposited in a rather close-lying mass (Fig. 4). The 
whole batch is laid in one night, or extending over 
two or three nights. The number of eggs deposited 
varies from about twenty to about seventy-five- 
rarely a larger number. Sixteen careful counts gave 
an average of forty-seven eggs. At the same time 
that the female deposits her eggs, she frequently, 
but not always, discharges a fluid which forms a 
very thin film over the surface of the water, which 
possibly assists in floating the eggs. The latter are 
of a jet-black color and, to the naked eye, cylin- 
drical in shape, one end of the egg being rounded 
and blunt, while the other is slightly pointed, the 
whole resembling closely a Conchita cigar. Thev 
measure about .65 mm. in length by .17 mm. in 
width, at the broadest part. Under a low power, 
the surface of the eggs is seen to be marked by tol- 
erably regular six-sided plates, each of which is 
further marked in the center by a little round ele- 
vation, which gives to the surface of the egg a deci- 
16 Fig. 8. Chart Showing the Mean Monthly Temperature of New Orleans and Havana for Ten Years; and the Relative Monthly Mortality from Yellow 
Fever in Havana from 1880 to 1899, and in New Orleans from 1847 to 1897. 
17 dedly roughened appearance (Fig. 5). Under this 
low amplification it is also seen that, while one side 
of the egg is somewhat convex, the other is flat or 
slightly concave and that a cross-section of the egg 
would present the appearance of a triangle instead 
of that of a cylinder. This flattening of the surface 
of the egg does not appear to extend quite to the 
ends, which are round in shape. Although floating 
perfectly if left undisturbed, any agitation of the 
water, especially of a rough character, is apt to cause 
some or a majority of the eggs to sink. If by slight 
pressure the egg is pushed beneath the surface of 
the water, it at once sinks and does not rise again. 
This sinking of the eggs does not interfere with their 
subsequent hatching, as in our experience submerged 
eggs furnish about as many larvae as those which 
are left floating on the surface. 
The resistance of stegomyia's eggs to external in- 
fluences is worthy of note. Drying seems to be but 
little injurious to their subsequent fertility. We 
have found that eggs dried on filter paper, and kept 
for periods of from ten to ninety days, will promptly 
hatch when again submerged in water. Dried eggs 
brought with us from Havana, in February, were 
easily hatched during the month of May, in Wash- 
ington, furnishing about 60 per cent, of the usual 
number of larvae hatched from fresh eggs. Freezing 
does not destroy the fertility of the eggs. Although 
freezing with a mixture of salt and ice for thirty 
minutes has several times seemed to prevent subse- 
quent hatching; on one occasion a batch of one hun- 
dred and fifty-five eggs, freshly deposited, which 
were frozen at a temperature of -170 C., for one hour, 
then thawed out at room temperature and placed 
in the incubator at 350 C., began to hatch on the 
sixth day, the majority furnishing active larvae on 
the eighth day. In another observation, freshly 
deposited eggs, frozen at-i7°C. for half an hour on 
18 Fig. 9.-Chart Showing Mean Monthly Temperature of Havana and Rio de Janeiro for Ten Years; and the Relative Monthly Mortality from Yellow 
Fever in Havana from 1880 to 1899 and in Rio de Janeiro from 1851 to 1883. 
19 two successive days, oegan to hatch on the third 
day as usual at incubator temperature. The resist- 
ance of stegomyia's eggs to drying for a period of 
three months would appear to demonstrate that 
this genus of mosquito could survive the winter in 
Havana, without the presence of hibernating females. 
Doubtless the genus is preserved in both ways. It 
is probable that the same could occur in our extreme 
southern latitudes. 
Length of Generation.-The impregnated female, 
having obtained a meal of blood, proceeds to deposit 
her eggs, in captivity, after an interval varying in 
our experience from two to thirty days-as a rule, 
the eggs are laid within seven days; sometimes a 
second or third meal of blood is taken before any 
eggs are laid. Eggs placed under favorable condi- 
tions of warmth, i. e. summer or incubator tempera- 
ture, begin to hatch, as a rule, on the third day, 
the period extending to about one week. The lar- 
val stage requires seven or eight days, and the pupal 
stage about two days. The period for the genera- 
tion may be stated, therefore, as follows: Incubation, 
three days; larval stage, seven days; pupal, two days; 
total, twelve days. As the eggs begin to hatch 
before the expiration of the third day, we generally 
obtain a few mosquitos on the eleventh day. The 
shortest period of development observed by us dur- 
ing summer weather in Cuba was incubation, two 
days; larval stage, six days; pupal, thirty-six hours: 
making the total length of this generation nine and 
a half days. This short period we believe to be 
quite exceptional. The first fully developed insects 
begin to emerge on the eleventh or twelfth day, and 
the whole number have reached maturity by the 
fifteenth or eighteenth day after deposition of the 
eggs. The young larvae, in emerging, rupture the shell 
at a point about one-fifth the length of the egg 
from the larger end. This cap-like end can be 
20 Fig. to.- Chart Showing Monthly Mortality from Yellow F«ver in the City of Havana for the Twenty Years, 1880 to 1899; for the Year 1900, and from 
January 1 to August 31, 1901. 
21 frequently seen turned back and still adhering to 
the rest of the shell (Fig. 5). 
The larva and pupa of stegomyia (Figs. 6 and 7) 
resemble fairly closely those of culex, and the larvae 
maintain the same relative position to the surface of 
the water, i. e. while in the act of breathing they as- 
sume a vertical position, with the head directed 
downward. 
Influence of Temperature on Propagation.-We have 
just seen that at summer temperatures the time re- 
quired for a complete generation of this insect is from 
eleven to eighteen days. We may say that at an 
average temperature of 750 F., or over, stegomyia 
multiplies abundantly. Exposure to a cooler tem- 
perature, even for a short time daily, much retards 
the development of this mosquito. Thus, a batch of 
fifty-one eggs kept at 350 C., but which were placed 
in a cool chamber at 200 C. for two hours daily during 
the whole process of development, although furnish- 
ing a few larvae at the end of the third day, were not 
all hatched until the eleventh day. The first pupae 
appeared on the fourteenth day and the first mosquito 
on the nineteenth day; the whole process being com- 
pleted in twenty-seven days, instead of the usual 
fifteen to eighteen days. The loss of insects was 
about 50 per cent. Eggs kept at a temperature of 
200 C. (68° F.) do not hatch, in our experience. 
Newly hatched larvae kept at this temperature develop 
very slowly and require about twenty days to reach 
the pupal stage. Mosquitos developed under such 
conditions are feeble, and but few arrive at maturity. 
Young larvae kept at 10° C. (500 F.) have failed to 
reach the pupal stage-although some growth takes 
place. In one experiment more than 50 per cent, 
were dead at the end of two weeks, and none sur- 
vived the thirty-second day. Half-grown larvae and 
pupae exposed to a temperature of 200 C., and even as 
low as io°C., continue to develop slowly, but the few 
22 insects which escape drowning have, as a rule, been 
of feeble strength and have refused to bite. Although 
the reduction of the temperature to the freezing point, 
or below, would not necessarily destroy the vitality 
of the eggs of this genus of mosquito, it should be 
remembered that a reduction of temperature to 68° F., 
or below, for even a few hours of the twenty-four, will 
much retard the development of the generation. At 
a temperature less than 68° F. the eggs of this insect 
have ceased to hatch. 
Influence of Temperature on Biting.-While the 
non-impregnated female does not appear to bite, the 
impregnated female is generally ready to bite on the 
second or third day of her existence; they very rarely 
suck blood on the first day. This species of mosquito, 
when not deprived of its liberty, although occasionally 
biting during the morning hours, has, in our experi- 
ence, been especially active from the hours of 4 p.m. 
till midnight. In captivity, the hungry impregnated 
female will bite at any hour of the day or night. The 
meal of blood appears to have been thoroughly di- 
gested on the third day, when the insects, if applied 
to the surface of the skin, can be again readily induced 
to feed. When freed in a room, the female does not 
appear to bite a second time till about five, or even 
seven, days have elapsed. 
As regards the effect of temperature on the stinging 
of stegomyia fasciata, the results of a number of 
observations made by us show that this mosquito 
will bite at temperatures of 62° F. and above. At 
temperatures below this point, we have not, as yet, 
succeeded in inducing even very hungry females to 
suck blood. We may, therefore, say that observa- 
tions thus far made appear to show that stegomyia 
fasciata, while not breeding at temperatures below 
68° F., will still bite at a temperature as low as 62° F., 
but probably not at lower temperatures. 
If this insect is concerned in the propagation of 
23 yellow fever, it is now quite apparent why an epidemic 
of this disease should fall to a low ebb in the city of 
New Orleans during the month of November, with a 
mean temperature of 6i.8° F., and practically cease 
in December, with a mean temperature of 55.30 F. 
A careful study of the charts herewith submitted 
(Figs. 8 and 9), showing the monthly mean temper- 
atures of the cities of Havana and New Orleans and 
Havana and Rio de Janeiro, together with the relative 
monthly mortality from yellow fever in these cities, 
will prove of interest, we think, as showing better 
than laboratory observations the general effect of 
temperature upon the breeding and biting of steg- 
omyia fasciata. In the light of recent researches, 
we can now understand that while yellow fever can, 
and does, prevail during the entire year in Havana 
and Rio de Janeiro-although at a comparatively low 
ebb during the winter months-it cannot propagate 
itself in New Orleans from December to May. 
Interval After Contamination Before the Mosquito Be- 
comes Dangerous.-In our experimental work on 
human beings, we have not succeeded in inducing an 
attack of yellow fever by the bites of mosquitos which 
had been kept less than twelve days after contamina- 
tion. The same insects which failed to convey the 
disease on the eleventh day were capable of so doing 
on the seventeenth day after infection. This interval 
of about twelve days, which appears necessary for 
the development of the parasite within the mosquito, 
plus the period of incubation, agrees with the time 
that has been observed to elapse between the intro- 
duction of an infecting case into a locality and the 
occurrence of the first secondary case, viz., two to 
three weeks. 
■ After the mosquito has once become dangerous, how 
long it remains capable of conveying the disease, al- 
though important, has not been determined. We 
have reported cases of yellow fever caused by the 
24 bites of stegomyia at intervals varying from twelve 
to fifty-seven days after contamination. Here the 
dangerous interval was forty-five days, but as one of 
these insects lived until the seventy-first day after 
biting a yellow-fever patient, the dangerous interval 
would here be prolonged to fifty-nine days, or a little 
over eight weeks. In our experience, the infected 
insect appears to live about as long as the non-infected 
mosquito, so that the answer to this question would 
depend upon the length of life of the mosquito. This 
we do not know. While in captivity, the majority of 
mosquitos do not survive, with the best of care, more 
than about five weeks, and many die within half of 
this time; we are ignorant as to the length of time 
during which they may live when under natural con- 
ditions. Certainly, during summer weather this will 
depend largely on the opportunity which the mosquito 
has of obtaining access to water. 
Measures to Prevent the Spread of the Disease When 
Imported.-A case of yellow fever having been im- 
ported into one of our seaport cities, we are now pre- 
pared to discuss the measures that should be taken 
to prevent its spread. The problem resolves itself 
into the simple one of excluding mosquitos from 
access to the sick individual and of destroying those 
insects that have already become infected. We can 
leave out of consideration any danger from wearing 
apparel or baggage, which, in our opinion, may be 
dismissed as harmless. 
The fear that has been entertained that infected 
insects may be imported in boxes or trunks, we be- 
lieve to be absolutely groundless, and this for the 
simple reason, as shown by numerous observations 
made by us, that mosquitos, when deprived of water, 
die within a few days. Even if allowed to fill them- 
selves with blood immediately before the experiment 
is begun, and then deprived of water, practically all 
are dead by the expiration of the fifth or commence- 
25 ment of the sixth day. We may say that of a large 
number of insects tried in this way, only one female 
has survived until the sixth day, and then in a feeble 
condition. Males and females which have been living 
on sugar and water, or fed two days before on blood, 
if deprived of water and food, begin to die after twenty- 
four hours, and all are dead on the fourth morning. 
Free access to water, therefore, is necessary for the 
existence of this mosquito. 
Add to the deprivation of water the chances of 
injury to so frail an insect packed in with articles 
of clothing, etc., and we see that infected mosquitos 
cannot be imported alive in baggage that has been 
five days en route. 
As the first special measure of prevention, then, 
we should give our prompt attention to the pro- 
tection of the sick individual against the bites of 
mosquitos. This can best be accomplished by 
thorough screening, without delay, of the windows 
and doors of the room occupied by the patient 
and with as little disturbance as possible, so that 
any insects already present in the room may be 
prevented from escaping. As it will not be feasible 
to make use of any of the destructive agents against 
mosquitos already within the patient's room until 
recovery, every precaution should be used to see 
that the insects do not escape in opening and closing 
the door. Screens at windows should not, for this 
reason, be movable. As it is possible that mos- 
quitos that have already bitten the sick individual 
may have escaped into other apartments of the 
house, these should be closed tightly and subjected 
either to sulphur or to formaldehyde disinfection, or 
to the fumes of burning pyrethrum. According to 
Dr. Gorgas, the efficient Health Officer of Havana, 
preference is given to pyrethrum powder, burned in 
the proportion of one pound to 1,000 cubic feet of 
26 air space.1 He, however, adds: "As the pyrethrum 
powder, even in this large quantity, does not cer- 
tainly kill all mosquitos, the room is opened at the 
end of three hours, and the mosquitos on the floor 
swept up and burned." 
We have mentioned above, in the order of their 
efficiency, the agents which are most destructive to 
stegomyia. According to our observations, an 
exposure for one and a half hours to sulphur fumiga- 
tion, in a well-closed room, in the proportion of one 
pound to 1,000 cubic feet of air space, will suffice 
effectually to destroy all mosquitos. Formalde- 
hyde gas is not quite so efficient. With Trenner's for- 
maldehyde generator, charged with* formalin, 900 
c.c.; glycerin, 9 c.c.; methyl alcohol, 360 c.c., which 
we have found quite reliable for the destruction of 
bacteria, an exposure of not less than three and 
preferably four hours is required in order to kill 
these insects in a tight room having 2,800 cubic feet 
capacity. Pyrethrum powder, if burned in the pro- 
portion of 4 oz. to 1,000 cubic feet of air 
space, will stupefy all mosquitos at the expiration 
of one hour, so that they will fall to the floor in a 
helpless condition. If used, however, the precau- 
tion above recommended by Dr. Gorgas should be 
strictly followed; that is, the room should be opened 
at the end of three hours, and all insects carefully 
swept up and burned. The practice of destroying 
all mosquitos in adjoining houses, as carried out in 
the city of Havana with such excellent results, we 
consider of the greatest importance, since only in 
this way can we hope to destroy infected mosquitos, 
and thus prevent the occurrence of secondary cases. 
In other words, relying upon the well-known slow 
progress of the spread of yellow fever, we seek to 
catch and destroy all mosquitos within a given 
1 Medical Record, New York, Vol. 60, No. io, Septem- 
ber 7, igoi. 
27 radius' of the first case. If secondary cases should 
occur, the same hygienic measures should be rigor- 
ously enforced along the lines above indicated. 
Upon the completion of the case, the room occupied 
by the patient should be disinfected, and in a matter 
where so much is at stake, we believe that sulphur 
should be given the preference as a disinfectant. In 
case of death, the body should be carefully screened 
against mosquitos, as stegomyia will bite the dead 
body, and might in this way acquire the parasite 
We have said nothing about the protection of 
non-immune individuals who enter the patient's 
room or house, since if the case under consideration 
is the infecting case, no danger is incurred. As the 
duration of the attack is short, generally less than 
ten days, the patient's room will have been disin- 
fected, and the infected mosquitos destroyed before 
they have become susceptible of conveying the 
disease to others. We desire to emphasize the fact 
that the interval elapsing between the infection of 
this mosquito by biting a case of yellow fever and 
the time when it has become capable of conveying 
the disease, viz. about twelve days, is of the utmost 
importance in our efforts toward stamping out yellow 
fever at its very commencement, since it furnishes 
a non-dangerous interval during which all infected 
insects should be easily destroyed. It thus makes 
the control of yellow fever, hereafter, a simpler and 
more certain matter than the suppression of an 
outbreak of any of the other acute infectious dis- 
eases. If non-immunes entering an infected house 
desire protection against the bites of stegomyia, 
this may be obtained by rubbing all exposed sur- 
faces of the body, including the ankle surfaces, with 
spirits of camphor, oil of pennyroyal, or a 5-per-cent. 
menthol ointment. The protective effect of these 
substances is, however, only temporary. 
What we have already said concerning the breed- 
28 ing places of stegomyia fasciola should sufficiently 
indicate the general hygienic measures that should 
be taken in order to prevent the spread of yellow 
fever. These should consist in enforcing such 
measures as will effectually destroy the breeding 
places of this very domestic mosquito. The methods 
adopted by the Chief Sanitary Officer of Havana, 
during the present year, may be taken as a model 
by our sanitary officials.1 It should not be for- 
gotten that a well-drained and well-sewered city, 
with a pure water supply and clean streets, has no 
protection against the spread of yellow fever, pro- 
vided rain-water barrels and other collections of 
water are present, in which stegomyia may breed. 
In one of the forts, on the outskirts of Havana, 
which was otherwise in an excellent sanitary-con- 
dition, we found thousands of stegomyia fasciata 
breeding in tin cans placed about the legs of a table 
in an officer's kitchen. Our conception of yellow 
fever, therefore, as a "filth" disease must be aban- 
doned, and our attention turned to yellow fever as 
a mosquito-borne disease. In illustration of what 
may be accomplished by sanitation based on the 
latter method of propagation, we present herewith 
a chart (Fig. 10) showing the actual monthly mortality 
from yellowfever in Havana, for the period from 1880 
to 1899, and also for the years 1900 and 1901. Com- 
paring the mortality from this disease for 1899, 
which was the most favorable year for yellow fever 
that Havana had experienced in twenty years, 
with 1901, during which sanitation, based on the 
demonstration that yellow fever is propagated by 
the mosquito, has been enforced, we find a reduction 
in mortality of 83.3 per cent, in favor of the present 
epidemic year (April 1 to August 31); or if we com- 
pare the mortality for the epidemic year 1900 with 
1 Medical Record, New York, Vol. 60, No. io, Septem- 
ber 7, 1901. 
29 the present year we observe a still greater reduction 
in favor of the latter, viz. 411 per cent. 
The sanitary regulations put into force February 
15, 1901, by Dr. Gorgas, resulted in freeing Havana 
from yellow fever within three months, so that for 
a period of fifty-four days-May 7 to July 1-no 
case occurred. On the latter date, the disease was 
brought into Havana from Santiago de las Vegas, 
and, according to Gorgas, has been introduced into 
the city at least a dozen times from this and other 
sources. In spite of these new sources of infection, 
July has only furnished four cases, with one death, 
and August eight cases, with two deaths. If such 
admirable results, under new methods of sanitation, 
have been obtained in this hotbed of yellow fever, 
we cannot believe that the intelligent and efficient 
boards of health of our cities will again permit this 
disease to assume an epidemic form in any city of 
the United States. 
Measures Directed Against the Importation of 
Yellow Fever Into the United States.-Under the 
admirable system of inspection and reports, as 
carried out by the Marine Hospital Service, the 
appearance of yellow fever at any foreign port is 
promptly reported for the information of the health 
authorities of our several Atlantic ports. We may, 
therefore, divide foreign ports within the so-called 
epidemic zone into (a) infected and (6) non-infected 
ports. Heretofore, no distinction has been made by 
the health officers of our Southern ports, as regards 
quarantine regulations from April 1 to November 1, 
between infected and non-infected places. All ports 
within the epidemic zone of yellow fever were con- 
sidered as being infected places, and hence passen- 
gers and vessels were subjected to quarantine and 
to disinfection of both baggage and cargoes. 
With our present knowledge of the way in which 
yellow fever is propagated, we believe that in the 
30 treatment of passengers, as well as of cargoes, a 
sharp distinction should be made, first, between 
infected and non-infected ports; and, secondly, in 
the case of vessels sailing from infected ports, be- 
tween those that have received their cargoes and 
passengers in mid-stream and those that have loaded 
at the wharf. 
We believe that no quarantine restrictions should 
be placed upon either passengers or cargo from non- 
infected ports. In the case of a vessel loading in 
mid-stream at an infected port by means of lighters, 
we believe that she can only receive infection in one 
way, i.e., by passengers who have been exposed to 
yellow fever on shore, and who, coming aboard, may 
thereafter be seized with the disease. The possi- 
bility of infected mosquitos reaching the vessel, either 
by flight or by means of lighters, may be considered 
as highly improbable. 
Vessels, loaded under the foregoing circumstances 
(t.^.,by lighters in mid-stream), and arriving at our 
ports without yellow fever developed en route 
should have their non-immune passengers quar- 
antined for five days, counting the time consumed 
by the voyage as part of the quarantine period, 
and should be allowed to discharge their cargoes 
without delay. If the disease has developed en 
route among crew or passengers, the sick should be 
promptly removed; the forecastle or staterooms, as 
the case may be, thoroughly disinfected with sul- 
phur or formaldehyde gas, and the vessel allowed 
to proceed to her wharf. 
On the other hand, if the vessel has received her 
cargo at the wharf of an infected port, there is a 
possibility that she may have received infection in 
three ways: First, either by contaminated mosquitos 
that have bitten a case of yellow fever in the imme- 
diate v cinity on shore; secondly, by mosquitos that 
have become infected from biting a yellow-fever pa- 
31 tient present on another vessel loading at the same, 
or at an adjacent, wharf; or, hirdly, by some indi- 
vidual who has acquired the infection on shore and 
afterward taken passage on the vessel. 
In our opinion, however, the chances of infection 
of a vessel by contaminated mosquitos coming aboard 
from a house or ship in close proximity are very 
slight; although such a possibility must be admitted, 
and the further possibility that recently infected 
mosquitos may have sought refuge on the vessel 
during the night preceding her day of departure. It 
is also possible that a case of mild, and hence unde- 
tected, yellow lever may occur on board, and be 
the source for the infection of mosquitos already 
present in the vessel. 
Under these circumstances, if a sufficient number 
of days have not elapsed between her port of depar- 
ture and port of arrival in the United States, i.e. 
sixteen to twenty-one days, to demonstrate the 
presence of infected mosquitos by the occurrence 
of a case or cases of yellow fever en route, we know 
of no way of absolutely excluding the possibility 
of importation of the disease by such a vessel than 
by the detention of all non-immune passengers for 
such number of days as will show their freedom 
from infection, and by careful disinfection of crew's 
and passengers' quarters. 
If more than twenty days have elapsed during the 
voyage, without the occurrence of yellow fever, we 
see no good reason why either passengers or vessel 
should be detained. 
We have said nothing about the disinfection of 
the vessel's cargo, for the reason that we do not 
consider this to be necessary. The only possible 
excuse for subjecting the cargo to disinfection would 
be the fear of the presence of infected mosquitos in 
the vessel's hold, provided she had loaded at the 
wharf of an infected port. In this instance, if the 
32 voyage has consumed five or more days, all mos- 
quitos contained in the hold will have died; for, as 
we have already pointed out, stegomyia jasciata 
lives only a few days if deprived of water. We 
cannot too strongly insist that the danger of importa- 
tion of yellow fever into the United States lies, not 
in cargo or personal baggage, but in the individual 
sick with that disease. With our present knowledge 
of its propagation, personal baggage should no longer 
be subjected to disinfection, and, with our increased 
ability to prevent its spread by measures easy of 
application, instances should be few and exceptional 
when a vessel coming from a yellow-fever port should 
be delayed longer than will be necessary to remove 
her non-immune passengers who have not yet com- 
pleted their period of five days since leaving the port 
of departure. 
The chief duty of quarantine officers hereafter 
will consist in the detection of mild or very mild 
cases of yellow fever. In a series of twelve cases 
of experimental yellow fever produced by the bite 
of stegomyia jasciata, we have, elsewhere,1 pointed 
out that four, or 33 per cent., were mild or very mild 
in character, and have indicated the difficulty of 
making a positive diagnosis in such cases. 
In discussing the period of incubation of experi- 
mental yellow fever, we have shown that in 16.6 
per cent, of our cases the period of incubation ex- 
ceeded the usual quarantine period of five days. 
If we add Carter's cases to those observed by our- 
selves, we find that of twenty-four cases the period 
■of incubation exceeded five days in three, or 12.5 
per cent. 
We can thus readily see what great danger here- 
tofore lay in the passage through quarantine of just 
1 " Experimental Yellow Fever," Transactions of the 
Association of American Physicians, Vol. XVI., 1901. 
33 such mild cases, or of those having an incubation 
stage of more than five days. 
While the exclusion of such cases is of the greatest 
importance, we doubt whether, with our improved 
knowledge of how to prevent the spread of yellow 
fever, it would be advisable to place a greater burden 
upon ships' passengers by extending the quarantine 
period to more than five days. It appears to us 
rather that in view of the troublesome delays to 
which passengers and vessels from yellow-fever ports 
have been subjected in the past, the time has now 
arrived, when, standing upon more solid ground, 
we will be justified in seeking in every way to lessen, 
as much as possible, the restrictions placed by 
present quarantine regulations upon the ship's 
cargo, while we add nothing to those of the pas- 
senger. 
To this end a most important part will have been 
accomplished if we can persuade the sanitary au- 
thorities of our sister republic, Mexico, and of the 
Central and South American States, to join us in 
the adoption of more enlightened methods for the 
suppression of this widely prevalent epidemic. 
34