THE GEOGRAPHICAL ASPECTS OF MALARIA ^ 



By Sib Malcolm Watson 



Director, Ross Institute of Tropical Hygiene 



London 



Had you asked me 50 years ago to address you on the "Geographical 

 Aspects of Mahiria," I should have begun by quoting from Hirsch's 

 monumental work on "Geographical and Historical Pathology" (1883) 

 as follows : 



Covering a broad zone ou botli sides of the Equator tlie malarial diseases 

 reach their maximum of frequency in tropical and subtropical regions. They 

 continue to be endemic for some distance into the temperate zone, with diminish- 

 ing severity and frequency towards the higher latitudes; in epidemic form they 

 not infrequently appear yet in other regions; and, in still wider diffusion wilh the 

 character of a pandemic, also beyond these indigenous latitudes. 



Hirsch follows this with pages describing the various countries 

 throughout the world in which the disease occurs, and an equally 

 extensive discussion of the conditions which influence the appearance 

 of the disease, and of its possible cause. But the discussions lead to 

 no final conclusions; and in the words of Duncan, writing in 1888: 

 "As Crudeli points out, malaria exists on soils of every conceivable 

 variety, of every age in geological time, and it is impossible to point 

 to any mineralogical or chemical conditions which can be said to 

 be essential." 



By his discovery in 1880 that malaria is caused by a living parasite, 

 visible under the microscope, Laveran, a French Army surgeon work- 

 ing in Algiers, made an important addition to our knowledge. Ma- 

 laria then ceased to be "a miasma," a word indicating some sort of 

 emanation from the soil; the word was not exactly defined; and, as 

 we have read, any sort of soil appeared capable of giving out the 

 emanation. Then came the problem. How does this parasite circu- 

 lating freely in man's blood pass from one victim to another? The 

 genius of Sir Patrick Manson, who had carried out original work in 

 China on another parasite circulating in the blood, provided a hy- 

 pothesis, which if not wholly correct provided Sir Ronald Ross with a 

 valuable starting point for his researches in India. Manson also 

 gave Ross the most generous and selfless help in other ways. 



1 Address delivered at meetiug of The Royal Geographical Society, London, February 9, 

 1942. Reprinted by permission from The Geographical Journal, vol. 99, No. 4, April 1942. 



501591—43 23 339 



