HUMAN DISEASES 519 



which is now under the direction of Sir Malcolm Watson and has 

 recently been incorporated with the London School of Hygiene 

 and Tropical Medicine, has been the centre for developments 

 which have arisen from the initial discovery, and has collaborated 

 with entomologists and medical men throughout the world. Some 

 conclusions now reached are as follows. To eliminate the disease 

 in any area it is not necessary to destroy all Anopheles, even of the 

 dangerous species. Drainage and agriculture are the old and 

 proved methods, but research since Ross's discovery has shown 

 that these may lead in some conditions to increase rather than 

 decrease of mosquitoes and malaria; for example in many places 

 drainage by open ditches is dangerous, since the environment 

 thereby produced is made more favourable for the malaria mos- 

 quitoes than some kinds of swamp and most wet forests. Other 

 examples are the selection of non-malarial sites for new houses, 

 and the removal of old houses to new and healthy sites; the use of 

 anti-malarial oils or paris-green to destroy mosquito larvae; the 

 preservation or destruction of forest or bush, as may be appropriate 

 to the locality; changing the chemical composition of water, as in 

 flooding dangerous coastal swamps with salt water, or converting 

 brackish water areas into fresh water, as practised with success in 

 Holland. 



Sir Malcolm Watson (1930), who has studied malarial conditions 

 in many parts of the world, including Africa, has summarized the 

 malaria policy of the Ross Institute and (1935) in his Finlayson 

 Memorial Lecture at Glasgow has described the great progress 

 achieved in the control of malaria since Ross's discovery. There 

 are, however, many parts of the world, formerly infected with 

 malaria, where the disease has practically ceased to exist as a result 

 of normal agricultural development without special anti-mosquito 

 campaigns; in many areas Anopheles have remained common after 

 the disease has disappeared. Europe provides such examples, 

 which were discussed at length by Dr. L. W. Hackett in his Heath 

 Clark Lectures of 1934 (published 1937)- 



With regard to Africa as a whole, the upholders of treatment as 

 the chief method of attack have stressed that since it is impossible 

 to eradicate Anopheles everywhere, its eradication from limited 

 areas might do more harm than good. The majority of Africans 



