THE SIERRA LEONE MALARIA-MOSQUITO.
[To THE EDITOR OF THE "SPECTATOR.']
SIR,—I hope in fairness to the originators of the mosquito theory of malarial infection, you will allow me to state in a few words what that theory is, unless some more competent exponent takes up the task. Both you and your correspon- dent, certainly the latter, seem to assume that on this theory a certain kind of mosquito produces malaria by its bite, just as the bite of a poisonous snake produces poisoning. The theory merely assumes that in malarious countries this mosquito ads as the host of the plasmodium malarice, a lowly organism of the existence of which and of its relation as vera causa to malaria, no one doubts who has studied the subject in the light of modern methods during the last fifteen years. This organism is taken up by the mosquito from human blood, developed further, and then passed on again. The mosquito no more originates malaria than the rat originates the plague, though few observers doubt that the latter propagates that disease. If there be no malaria in Rangoon, it is just as reasonable to ask why mosquito-bites there do not produce malarial fever as to ask why London rats do not carry the plague. As to the question in youlr note why all mosquito-bites in a malarious country do not produce malaria, and why any persons escape, it can only be said that the same applies to all infectious diseases (not, of course, reckoning malaria as such). Why do ten people drink an infected milk or water supply, and only two get typhoid fever ? Why are negroes largely exempt from yellow fever, some tribes entirely ? Until the vast problem of immunity is more thoroughly worked out, no answer cap be given to this and many similar questions.—I am, Sir, &c., E. H.
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