MALARIA — WATSON 341 



was to mislead rather than guide. For the truth is that only a few 

 anopheles carry malaria in nature, although all anopheles can be in- 

 fected in a laboratory ; which made the prevention of malaria appear 

 to be much more difficult than it eventually proved to be. 



This paper must describe just what mosquitoes carry malaria in the 

 main geographical areas, something of the very different conditions 

 in which they live, and the strange ways we have invented to control 

 or destroy them. The story begins in Malaya. After seeing Malaya 

 in 1926, Koss told the Committee of the Koss Institute that the anti- 

 malarial work done there was the greatest sanitary achievement 

 ever accomplished in the British Empire, as it was also the first suc- 

 cessful antimalarial work carried out in the British Empire, if not 

 in the world. (Ann. Rep. Ross Inst., 1927.) 



The Malay Peninsula consists mainly of ranges of granite moun- 

 tains, and coastal plains with fresh-water swamps fringed by man- 

 grove with salt and brackish water; all three are covered by great 

 forests. Man lives there always at war with the jungle. 



It was my privilege to live in the Peninsula from 1900 to 1928, to 

 take an active part in research, and initiate the practical work for 

 the control of malaria (Watson, 1903). In the part of the mangrove 

 forest zone covered by every tide, no dangerous anopheles live and 

 there is no malaria; but in the inner part, covered only by spring 

 tides. Anopheles uinbrosus breeds and carries malaria. If the man- 

 grove forest be felled, another anopheles appears and this new- 

 comer also carries malaria; today it is called A. sundawns. Both 

 mosquitoes disappear when the swamp is embanked and drained. In 

 1901 Port Swettenham was saved from closure by embanking, drain- 

 ing, and oiling of pools, and a very complete organization for the 

 medical care of the people. The order to close it had actually been 

 given by the Governor, Sir Frank Swettenham, 2^/^ months after it 

 was opened, but was not carried into effect when all the facts were 

 put before him by me. 



The coastal plains — great swamps deeper and wider than any- 

 thing in Italy — harbor A. mribrosus and are intensely malarial. 

 Here drainage, and selection of sites of houses half a mile from the 

 undrained jungle, gives 100 percent protection against malaria. 



Attention was next turned to the hills where it was not possible to 

 get rid of the mosquito by the simple method of drainage. The 

 coastal hills are, when under forest, intensely malarial, because A. 

 uinbrosus lives in the valleys, while the inland hills are healthy 

 under forest, because A. umbrosus does not live there. Both kinds 

 of hill land are intensely malarial when the forest is felled, because 

 yet a third mosquito appears in the picture: A. maculatus. It lives 

 in sunshine, and in even the steepest mountain streams, but not 

 where the streams are covered by jungle. This insect causes intense 



