248 BACOT : MOSQUITOES AND THE DANGER OF MALARIA. 
recent writer suggests that, among other purposes, it is of service 
to wash out any him 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 tropica.1 
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, PI. v.). 
We have, however, another species of Mosquito (Theobaldia 
annulatci) (figs. 4 and 5, PI. v.) which bears some superficial 
