248 BACOT: MOSQUITOES AND THE DANGER OF MALARIA.
recent writer suggests that, among other purposes, it is of service
to wash out any film of blood that may remain in the tube
after feeding.
The irritation which follows the bite of mosquitoes and
other blood-sucking insects is probably due to the action of
the salivary fluid, and may be only incidental to its action for
these purposes. The broad facts suggest, however, that this
irritation is purposive and is associated with the dilation of the
very small blood vessels or capillaries, thus producing a readily-
available supply of blood within the radius of the insects' suction.
Schaudin suggested that the weal produced by mosquito-bites
was caused by an enzyme due to the presence of yeast organisms
in the diverticula of the oesophagus. Weals are, however, some-
times produced by the bites of bugs, lice, or fleas, which do not
possess diverticulae of the oesophagus and whose stomachs
appear normally to be relatively, if not actually, sterile.
III.—MOSQUITOES AND THE DISSEMINATION OF DISEASES.
Our present exact knowledge of the part taken by mosquitoes
in transmitting disease is due to many devoted workers, among
whom may be mentioned Grassi, Laveran, Manson, and Ross
in regard to Malaria ; to the members of the United States Army
Commission, Drs. Reed, Carol, Lazear, and Agramonte in the
case of Yellow Fever ; and to Manson as regards Elephantiasis.
The connection between mosquitoes and disease had. however,
been suspected and written about by earlier workers on tropical
diseases during the nineteenth century ; while, as a popular
belief, it was current in widely-separated countries from very
early times ; for the device of mosquito curtains was known
to, and used by, the ancient Egyptians.
As a result of the labours of Ross and numerous later workers.
it is now established that Malaria fever is transmitted by certain
species of mosquitoes belonging to the section Anopheles only.
Consequently, it is of great practical importance that all the
special characters of this group should be carefully studied and
that the distinctive features which separate them in egg, larval,
and adult stage from the other tribes of mosquitoes should be
clearly charted. In Britain, the commonest and most important
species of Anopheles is A. maculipennis (figs. 2 and 3, Pl. v.).
We have, however, another species of Mosquito (Theobaldia
annulata) (figs. 4 and 5, Pl. v.) which bears some superficial