342 ANNUAL REPOiRT SMITHSONIAN INSTITUTION, 1942 



malaria although there may not be a swamp within miles. In Malaj'a 

 yearly death rates of 300 per 1,000 were not uncommon among labor 

 forces on estates or on engineering works before effective means to 

 control mosquitoes were devised. 



Among the important discoveries in Malaya were the following : 



Only 3 out of some 30 species of anopheles in Malaya carry 

 malaria. We had to kill only the dangerous species to stamp out 

 the disease; the others could be ignored. This is called "species 

 sanitation" (Watson, 1911). 



Many dangerous-looking swamps, including rice fields on the 

 coastal plains, were not malarial (Watson, 1911). 



In 1914 I prepared a mixture of mineral oils which rapidly killed 

 all anopheles in even fast-running streams, but was not poisonous 

 to men or animals. This solved a difficult problem, the intense 

 malaria produced by stream -breeding anopheles. By means of this 

 mixture malaria was rapidly brought under control over large areas, 

 including rubber estates, at practically no capital cost. 



In 1909 I realized that Nature controlled species of anopheles in 

 several ways, and that by imitating her we could control malaria 

 at little or no expense in many places (Strickland, 1915; Williamson, 

 1933). This was sometimes unconsciously achieved by the planters 

 when they opened up the estates. Four years' research on estates 

 showed that the change of species that occurred from time to time 

 was due to changes in the conditions in the valleys. When under 

 jungle there was one species (A. unibrosus) that carried malaria; 

 when the jungle was felled and the streams freed from grass, a new 

 species appeared {A. inaculatiLs) which also carried malaria; in 

 intermediate conditions of the stream there were half a dozen species 

 that did not carry malaria. The knowledge of how to change species 

 was a notable advance and is today the foundation of a great deal of 

 antimalarial precautions taken in so many parts of the world. Our 

 researches also enabled us to know where to house the people, and 

 thus deaths were reduced to 4.9 per 1,000. 



Another method devised as a result of later researches was inter- 

 mittent sluicing which has a devastating effect even on mosquitoes 

 that live in running water. Devised in Malaya, and capable of being 

 operated by the Malay peasant, this method spread to southern India. 

 Today in some of the bigger streams in the Himalayas there are bat- 

 teries of sluices. (Williamson, 1933.) 



The researches and many inventions for the control of malaria in 

 Malaya carried out by the Government and the rubber planters have 

 thrown a flood of light on the disease in other geographical regions. 

 So I have spoken of it in some detail. Of the work done in Malaya, 

 Professor Swellengrebel wrote in 1935: "The principle forming the 

 base of malaria control in Malaya ought to be the principle under- 



