In short, science is prepared to say to the community: "I have done my part in the problem of malaria. It is for you to do the rest." There is literally no neighborhood in the temperate zone, and exceedingly few in the tropics, which cannot, by intelligent coöperation and a moderate expense, be absolutely rid first of malaria, and second of all mosquito-pests. It is only a question of intelligence, coöperation, and money. The range of flight of the ordinary mosquito is seldom over two or three hundred yards, save when blown by the wind, and more commonly not more than as many feet, and thorough investigation of the ground within the radius of a quarter of a mile of your house will practically disclose all the danger you have to apprehend from mosquitoes. It is a good thing to begin with your own back yard, including the water-butt, any puddles or open cesspools or cisterns, and any ornamental water gardens or lily-ponds. These latter should be stocked with fish or slightly oiled occasionally. If there be any accumulations of water, like rain-barrels or cisterns, which cannot be abolished, they should either be kept closely covered or well screened with mosquito netting.
It might be remarked incidentally in passing, that the only really dangerous sex in mosquitodom, as elsewhere, is the female. The male mosquito, if he were taxed with transmitting malaria, would have a chance to reëcho Adam's cowardly evasion in the Garden of Eden, "It was the woman that thou gavest me." Both sexes of mosquitoes under ordinary conditions are vegetable feeders, living upon the juices of plants. But when the female has thrown upon her the tremendous task of ripening and preparing her eggs for deposition, she requires a meal of blood—which may be a comfort to our vegetarian friends, or it may not. Either she requires a meal of blood to nerve her up to her criminal deed, or, when she has some real work to do, she has to have some real food.
The mosquito-brigade have still another method of checking the spread of malaria, at first sight almost a whimsical one,—no less than screening the patient. The mosquito, of course, criminal as she is, does not hatch the parasites de novo in her own body, but simply sucks them up in a meal of blood from some previous victim. Hence by careful screening of every known case of malaria, mosquitoes are prevented from becoming infected and transmitting the disease. Instead of the screens protecting the victims from the mosquitoes, they protect the mosquitoes against the victim.
This explains why hunters, trappers, and Indians may range a region for years, without once suffering from malaria, while as soon as settlers begin to come in in considerable numbers, it becomes highly malarious. It had to be infected by the coming of a case of the disease.
The notorious prevalence of malaria on the frontier is due to the introduction of the plasmodium into a region swarming with mosquitoes, where there are few window-screens or two-story houses.
No known race has any real immunity against malaria. The negro and other colored races, it is true, are far less susceptible; but this we now know applies only to adults, as the studies of Koch in Africa showed that a large percentage of negro children had the plasmodium in their blood. No small percentage of them die of malaria, but those who recover acquire a certain degree of immunity. Possibly they may be able to acquire this immunity more easily and with less fatality than the white race, but this is the extent of their superiority in this regard. The negro races probably represent the survivors of primitive men, who were too unenterprising to get away from the tropics, and have had to adjust themselves as best they might.
The serious injury wrought in the body by malaria is a household word, and a matter of painfully familiar experience. Scarcely an organ in the body escapes damage, though this may not be discovered till long after the "fever-and-ague" has been recovered from.
As the parasite breeds in the red cells of the blood, naturally its first effect is to destroy huge numbers of these, producing the typical malarial anæmia, or bloodlessness. Instead of 5,000,000 to the cubic centimetre of blood the red cells may be reduced to 2,000,000 or even 1,500,000. The breaking down of these red cells throws their pigment or coloring-matter afloat in the blood; and soaking through all the tissues of the body, this turns a greenish-yellow and gives the well-known sallow skin and yellowish whites of the eyes of swamp-dwellers and "river-rats."
The broken-down scraps of the red blood-cells, together with the toxins of the parasite, are carried to the liver and spleen to be burned up or purified in such quantities that both become congested and diseased, causing the familiar "biliousness," so characteristic of malaria.
The spleen often becomes so enormously enlarged that it can be readily felt with the hand in the left side below the ribs, so that it is not only relied upon as a sign of malaria in doubtful cases, but has even received the popular name of the "ague-cake" in malarious districts.