ESSAYS 463 



announced his epoch-making discovery that the parasite causing malarial 

 fever could, and could only, be transmitted from one person to another by the 

 successive bites of the same mosquito. It was subsequently shown that 

 many kinds of mosquitoes were capable of acting as " malaria carriers," 

 but that all those possessing this undesirable gift belonged to one particular 

 genus, namely the Anopheles.'^ 



As soon as the above facts became public property, it was correctly sur- 

 mised that districts in which malarial fever was prevalent might be made 

 healthy by a wholesale destruction of the mosquitoes responsible. As is 

 well known, the larval and pupal stages of the mosquito are passed in water, 

 the duration of the former being something like two or three weeks, and that 

 of the latter about as many days. The larva is a well-known " wriggly " 

 creature, generally to be observed hanging head downwards with its tail-like 

 breathing-tube just breaking the water surface. Mosquito larvae are very 

 easily destroyed, either by mixing some poisonous substance with the water, 

 or by covering its surface with a film of oil, which prevents the larvae from 

 breathing, and causes them to drown. Of the two methods, the latter is 

 usually much the cheaper, and thus we find that oil-spraying, assisted as far 

 as possible by drainage operations, forms the basis of practically all the anti- 

 mosquito schemes now being worked in various parts of the world. 



The earlier mosquito campaigns were naturally confined to districts in 

 which malaria was prevalent, and the successful operation of numerous 

 schemes, extending over large tracts of country and supported in many cases 

 by official funds and by special legislation, fully demonstrated the prac- 

 ticability of abolishing mosquitoes (and, in consequence, mosquito-carried 

 disease) from any locality desired. 



The defeat of the Anopheles mosquitoes gave rise to the suggestion that 

 anti-mosquito measures might with advantage be adopted in towns and 

 villages to minimise the often intolerable nuisance due to the prevalence 

 of " harmless " mosquitoes (as the many " non-malarial " kinds are popularly, 

 though very erroneously called), with the result that a great number of 

 " unofficial," schemes, depending largely upon voluntary subscriptions and 

 upon voluntary work, are in existence (especially in the United States) at 

 the present time. 



We may, then, roughly separate anti-mosquito organisations into the two 

 following classes : 



(I) The Official type, operating in a district where a mosquito-conveyed 

 disease and the appropriate mosquitoes co-exist, and usually aided by of&cial 

 funds, labour, legislation, etc. 



(II) The Unofficial type, operating in a district for the purpose of mini- 

 mising the nuisance due to the prevalence of mosquitoes of all kinds, and 

 unassisted (at any rate in the early stages) by municipal funds, labour, 

 by-laws, etc. 



• ■ • • • 



There is no question that the subject of mosquito control is much better 

 understood abroad than it is in this country. In England, indeed, the 

 opinion of '' the man in the street " is almost invariably based upon three 

 distinct fallacies, namely, that English mosquitoes (i) are all " non-malarial " 

 ones, and (ii) are perfectly harmless, though admittedly a source of (iii) 

 unavoidable annoyance. These three fallacies must be dealt with separately. 



(i) Of the total of twenty-five known British mosquitoes, three are malaria- 

 carriers of the Anopheles genus, two of them being distributed freely all 

 over England. During the war, the frequent co-existence in military areas 

 of malaria " cases " and Anopheles mosquitoes led to many epidemics of 



^ In the year 1900 a precisely similar connection was proved to exist 

 between the disease of yellow fever and a particular mosquito, Stegomyia 

 fasciata. 



