IX] MALARIA IN RELATION TO MAN I45 



The part played by Anopheles in the transmission of malaria 

 is often distinctly modified by the method of life and customs 

 of man. Thus the type of dwelling may be such as to minimize 

 the chances of Anopheles obtaining human blood or, on the other 

 hand, to greatly favour such a chance. Thus, the introduction 

 of glass windows into English houses may well have hastened 

 the disappearance of malaria from this country. Again, 

 communities, by housing cattle or other domestic animals, 

 often favour the occurrence of Anopheles, whilst the amount of 

 clothing worn and special modes of hvelihood, may similarly 

 affect the prevalence of malaria. 



Malaria in Relation to Man. 



So long as man was supposed to be the victim of animal- 

 culae, that before entering his body lived a free life in marsh 

 water, etc., the part man himself played in the continuance and 

 preservation of the parasite was not considered. But as we 

 now understand the rationale of malaria transmission, it is 

 evident that man, no less than the mosquito, is essential to the 

 continued life of the parasite, and the nature of man's influence 

 as a host is at least equal in importance to those circumstances 

 we have discussed in the previous section. 



It will be evident from what has already been said that it 

 is man and not the mosquito which forms the chief reservoir 

 of infection. A man once infected, even though no longer 

 exposed to re-infection, may harbour the parasite for years. 



So long as he does so, and is liable to relapses with the 

 formation of gametes, such a man is capable of infecting mos- 

 quitoes and of restarting active transmission of the disease. 

 The ability to maintain a prolonged state of infection in man 

 is therefore a very valuable asset to the parasite, and all con- 

 ditions which favour or are adverse to a maintenance of the 

 parasite in the blood of man are of epidemiological importance. 

 Similarly, the amount of infection passed on to the mosquito 

 has been shewn to be an important matter, a mosquito which 

 has taken in blood containing many gametes being capable 

 of giving rise to a much more severe infection than one which 



