434 THE BIOLOGY OF INSECTS 



Malaria was formerly a common and dangerous disease in 

 England well known to physicians as ** ague " ; it was 

 especially prevalent and indeed epidemic in the fen district 

 of the eastern counties and the marshy regions of the 

 Thames valley and the Channel coast. G. H. F. Nuttall 

 and his colleagues pointed out (1901) that the British 

 species of Anopheles are much more frequent in these 

 localities than in western and northern districts. It appears 

 that malaria or ague ceased to be an epidemic disease in 

 England about the year i860. From the ascertained facts 

 Nuttall and his fellow-workers conclude that the former 

 distribution of the disease was " not a matter of the geo- 

 graphical distribution of Anopheles as much as of their 

 numerical distribution." The anopheline population became 

 much reduced by the drainage of fens and marshes, while 

 the human population of these districts was reduced by 

 emigration into cities or overseas, and the use of quinine in 

 medical treatment tended to destroy the Plasmodia in 

 human blood. Thus the chances of infection became so 

 greatly lessened that the disease died out. It is clear, 

 however, that the return of a number of infected persons 

 from tropical malarial districts, might result in the re- 

 introduction on a great scale of malaria into this country. 

 Its disappearance here affords strong evidence that mosquito- 

 borne disease may be checked without complete extermina- 

 tion of the insects concerned if their numbers in the neigh- 

 bourhood of human dwellings be drastically reduced. This 

 has been shown by the action of Ross and others in many 

 hitherto deadly tropical regions, to be feasible and effective. 

 A large culicine mosquito, formerly known generally 

 as Stegomyia fasciata but now usually referred to in entomo- 

 logical literature under the name Aedes argenteus, with a 

 wide distribution in the tropics and warmer regions of the 

 world, is of very great importance as the transmitter of the 

 organism (a spirochaet) which causes yellow fever, one of 

 the most dangerous of tropical and sub- tropical diseases. 

 J. W. Folsom (1923) describes vividly the high mortality 

 in the United States during the nineteenth century, over 



