440 THE PRESIDENT'S ADDRESS. 



half the total disease in the Tropics. It occurs under at 

 least three forms, known commonly as tertian, quartan, 

 and pernicious malaria, each of them easily distinguishable 

 clinically, and due to distinct species of the parasite differing 

 from one another in morphological characters, but similar in 

 the general features of their life- cycle. 



Until comparatively recent times nothing whatever was 

 known of the nature of malaria, or the manner in which it 

 was acquired. It was generally believed that it was due to a 

 poisonous miasma which arose from swamps and marshes, a 

 notion conveyed in the name malaria — " bad air." This miasma 

 theory is very prevalent in literature ; for instance, in such a 

 work as Dickens's " Martin Chuzzlewit," where the unfortunate 

 settlers in Eden are supposed to contract fever by breathing 

 the exhalations of the swamps. 



The scientific study of malaria may be dated from 1880, when 

 the parasite was discovered in the blood of fever patients by 

 Laveran, then a military surgeon in Algiers. Laveran examined 

 the blood microscopically, and observed the principal phases of 

 the parasite. It was, however, some years before Laveran's 

 parasite was accepted as the cause of malaria, though it ulti- 

 mately obtained universal recognition. Even then it remained 

 a mystery how the parasite got into the blood, and many still 

 held to the miasma-theory. It was supposed by some that the 

 parasite passed out of the body and produced cysts or spores 

 which could be disseminated by the wind, just as the cysts of 

 many Infusoria are known to be carried by aerial currents, and 

 that by inhaling these air-borne germs the disease was acquired. 

 Others sought for the source of the infection in the contamination 

 of drinking-water. 



It remained for a countryman of ours to discover the true 

 method of infection. Prof. Ronald Ross, then in the Indian 

 Medical Service, experimented first with the very similar malarial 

 parasites of birds, and found that the infection was taken from 

 one bird to another by mosquitoes of the genus Culex. Similar 

 experiments on human malaria gave at first negative results, 

 until it was discovered that the necessary intermediate host of 

 human malaria was a mosquito belonging to quite a different 

 genus, Anopheles. These experiments were confirmed by many 

 investigators in all parts of the world, and led to results which 



