ORIGIN AND DEVELOPMENT OF THE MOSQUITO THEORY
The possible agency of insects in the propagation of yellow fever was
thought of by more than one observer, from a very early period in the
history of this disease. For instance, Rush, of Philadelphia, in 1797,
noticed the excessive abundance of mosquitoes during that awful epidemic.
Subsequently, several others spoke of the coincidence of gnats
or mosquitoes and yellow fever, but without ascribing any direct relation
to the one regarding the other. Of course, man-to-man infection
through the sole intervention of an insect was a thing entirely
inconceivable and therefore unthought of until very recently, and in truth
the discovery, as far as yellow fever is concerned, was the result of a
slow process of evolution of the fundamental fact, taken in connection
with similar findings, in other diseases.
The earliest direct reference is found in the writings of Dr. Nott, of
Mobile, Ala., who in 1848 suggested that the dissemination of the yellow-fever
poison was evidently by means of some insect "that remained
very close to the ground.'' But the first who positively pointed to the
mosquito as the spreader of yellow fever, who showed that absence of
mosquitoes precluded the existence of the disease and who prescribed
the ready means to stamp it out, by fumigation and by preventing the
bites of the insects, was Dr. Louis D. Beauperthuy, a French physician,
then located in Venezuela. The writer has an original copy of his
paper, published in 1853, where he fastens the guilt upon the domestic
mosquitoes, believing, in accord with the prevailing teachings of medical
science, that the mosquitoes infected themselves by contact or feeding
upon the organic matter found in the stagnant waters where they
are hatched, afterwards inoculating the victims by their sting. He
recognized the fact that yellow fever is not contagious and therefore
could not think of the possibility of man-to-man infection, as we know
it to-day. The keenest observer was this man Beauperthuy, and, even
at that benighted time in the history of tropical medicine, made most
interesting studies of the blood and tissues, employing the microscope
and the chemical reactions in his research. No one believed him, and
a commission appointed to report upon his views said that they were
inadmissible and all but declared him insane.
This field of investigation remained dormant for a comparatively
long period of time. Meanwhile another medical writer, Dr. Greenville
Dowell, mentions in 1876, that "if we compare the effect of heat and
cold on gnats and mosquitoes with yellow fever, it will be difficult to
believe it is of the same nature, as it is controlled by the same natural
laws.'' Soon after this, in 1879, the first conclusive proof of the direct
transmission of a disease from man-to-man was presented by the father
of tropical medicine, Sir Patrick Manson, with regard to filaria, a blood
infection that often causes the repulsive condition known as elephantiasis
and which the mosquito takes from man and after a short time gives
over to another subject. This discovery attracted world-wide attention
and many looked again towards the innumerable species of biting
insects that dwell in the Tropic Zone, as possible carriers of the obscure
diseases which also prevail in those regions.
In 1881, Dr. Carlos Finlay, of Havana, in an exhaustive paper read
before the Royal Academy of Sciences, gave as his opinion that yellow
fever was spread by the bites of mosquitoes "directly contaminated by
stinging a yellow fever patient (or perhaps by contact with or feeding
from his discharge).'' This latter view he held as late as 1900, which,
although correct in the main fact of the transmission of the germ from
a patient to a susceptible person by the mosquito, the modus
operandi,
as he conceived it, was entirely erroneous.
Dr. Finlay, unfortunately was unable to produce experimentally
a single case of fever that could withstand the mildest criticism, so that
at the time when the Army Board came to investigate the causes of
yellow fever in Cuba, his theory, though practically the correct one,
had been so much discredited, in a great measure by his own failures,
that the best-known experts considered it as an ingenious, but wholly
fanciful, one and many thought it a fit subject for humorous and
sarcastic
repartee. Finlay also believed, erroneously, that repeated
bites of contaminated insects might protect against yellow fever and
that the mosquitoes were capable of transmitting the germ to the next
generation.
The wonderful discoveries of Theobald Smith, as to the agency of
ticks in spreading Texas fever of cattle, and those of Ross and the
Italian investigators who showed conclusively that malaria was transmitted
by a species of mosquito, brought the knowledge of these various
diseases to the point where the Army Board took up the investigation
of yellow fever.
