Part 15 (1/2)
Granted that mosquitoes do cause and are the only cause of malaria, what are you going to do about it? At first sight any campaign against malaria which involves the extermination of the mosquito would appear about as hopeless as Mrs. Partington's attempt to sweep back the rising Atlantic tide with her broom. But a little further investigation showed that it is not only within the limits of possibility, but perfectly feasible, to exterminate malaria absolutely from the mosquito end. In the first place, it was quickly found that by a most merciful squeamishness on the part of the plasmodium, it could live only in the juices of one particular genus of mosquito, the _Anopheles_; and as nowhere, not even in the most benighted regions of Jersey, has this genus been found to form more than about four or five per cent of the total mosquito population, this cuts down our problem to one-twentieth of its apparent original dimensions at once. The ordinary mosquito of commerce (known as _Culex_) is any number of different kinds of a nuisance, but she does not carry malaria.
Here the trails of the extermination party fork, one of them taking the perfectly obvious but rather troublesome direction of protecting houses and particularly bedrooms with suitable screens and keeping the inhabitants safely behind them from about an hour before sundown on. By this simple method alone, parties of explorers, of campers, of railroad-builders going through swamps, of the laborers on our Panama Ca.n.a.l, have been enabled to live for weeks and months in the most malarious regions with perfect impunity, so long as these precautions were strictly observed. The first experiment of this sort was carried out by Bignami upon a group of laborers in the famous, or rather infamous, Roman Campagna, whose deadly malarial fevers have a cla.s.sic reputation, and has achieved its latest triumphs in the superb success of Colonel Gorgas at Panama. While this procedure should never be neglected, it is obvious that it involves a good deal of irksome confinement and interferes with freedom of movement, and it will probably be carried out completely only under military or official discipline, or in tropical regions where the risks are so great that its observance is literally a matter of life or death.
The other division of malaria-hunters pursued the trail of the _Anopheles_ to her lair. There they discovered facts which give us practically the whip-hand over malarial and other tropical fevers whenever we choose to exercise it. It had long been known that the breeding-place of mosquitoes was in water; that their eggs when deposited in water floated upon the surface like tiny boats, usually glued together into a raft; that they then turned into larvae, of which the well-known ”wigglers” in the water-b.u.t.t or the rain-barrel are familiar examples; and that they finally hatched into the complete insect and rose into the air.
Obviously, there were two points at which the destroyers might strike, the egg and the larvae. It was first found that, while the eggs required no air for their development, the larvae wiggled up to the surface and inhaled it through curious little tubes developed for this purpose, oddly enough from their tail-ends. If some kind of film could be spread over the surface of the water, through which the larvae could not obtain air, they would suffocate. The well-known property of oil in ”sc.u.mming over” water was recalled, two or three stagnant pools were treated with it, and to the delight of the experimenters, not a single larva was able to develop under the circ.u.mstances. Here was insecticide number one. The cheapest of oils, crude petroleum, if applied to the pool or marsh in which mosquitoes breed, will almost completely exterminate them. Scores of regions and areas to-day, which were once almost uninhabitable on account of the plague of mosquitoes, are now nearly completely free from these pests by this simple means. An ounce to each fifteen square feet of water-surface is all that is required, though the oiling needs to be repeated carefully several times during the season.
But what of the eggs? They require no air, and it was found impossible to poison them without simply saturating the water with powerful poisons; but an unexpected ally was at our hand. It was early noted that mosquitoes would not breed freely in open rivers or in large ponds or lakes, but why this should be the case was a puzzle. One day an enthusiastic mosquito-student brought home a number of eggs of different species, which he had collected from the neighboring marshes, and put them into his laboratory aquarium for the sake of watching them develop and identifying their species. The next morning, when he went to look at them, they had totally disappeared. Thinking that perhaps the laboratory cat had taken them, and overlooking a most contented twinkle in the corner of the eyes of the minnows that inhabited the aquarium, he went out and collected another series. This time the minnows were ready for him, and before his astonished eyes promptly pounced on the raft of eggs and swallowed them whole. Here was the answer at once: mosquitoes would not develop freely where fish had free access; and this fact is our second most important weapon in the crusade for their extermination. If the pond be large enough, all that is necessary is simply to stock it with any of the local fish, minnows, killies, perch, dace, ba.s.s,--and presto! the mosquitoes practically disappear. If it be near some larger lake or river containing fish, then a channel connecting the two, to allow of its stocking, is all that is required.
On the Hackensack marshes to-day trenches are cut to let the water out of the tidal pools; while in low-lying areas, which cannot be thus drained, the central lowest spot is selected, a barrel is sunk at this spot, and four or five ”killie” fish are placed in it. Trenches are cut converging into this barrel from the whole of the area to be drained, and behold, no more mosquitoes can breed in that area, and, in the language of the day, ”get away with it.”
Finally, most consoling of all, it was discovered that, while the ordinary _Culex_ mosquito can breed, going through all the stages from the egg to the complete insect, in about fourteen days, so that any puddle which will remain wet for that length of time, or even such exceedingly temporary collections of water as the rain caught in a tomato-can, in an old rubber boot, in broken crockery, etc., will serve her for a breeding-place, the _Anopheles_ on the other hand takes nearly three months for the completion of her development. So that, while a region might be simply swarming with ordinary mosquitoes, it would frequently be found that the only places which fulfilled all the requirements for breeding-homes for the _Anopheles_, that is, isolation from running water or larger streams, absence of fish, and persistence for at least three months continuously, would not exceed five or six to the square mile. Drain, fill up, or kerosene these puddles,--for they are often little more than that,--and you put a stop to the malarial infection of that particular region. Incredible as it may seem, places in such a hotbed of fevers as the west coast of Africa, which have been thoroughly investigated, drained, and cleaned up by mosquito-brigades, have actually been freed from further attacks of fever by draining and filling not to exceed twenty or thirty of these breeding-pools.
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 cooperation and a moderate expense, be absolutely rid first of malaria, and second of all mosquito-pests. It is only a question of intelligence, cooperation, 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-b.u.t.t, 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 acc.u.mulations 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 pa.s.sing, that the only really dangerous s.e.x in mosquitodom, as elsewhere, is the female. The male mosquito, if he were taxed with transmitting malaria, would have a chance to reecho Adam's cowardly evasion in the Garden of Eden, ”It was the woman that thou gavest me.” Both s.e.xes 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 _anaemia_, 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 sc.r.a.ps 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 quant.i.ties 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.
So full is the blood of the parasites, that they may actually choke up the tiny blood-vessels and capillaries in various organs, so as to block the circulation and cause serious and even fatal congestions.
Obstructions of this sort may occur in the brain, the liver, the coats of the stomach, or intestines, and the kidneys; and they are the chief cause of the deadly ”congestive chills,” or pernicious malarial paroxysms, which we have alluded to.
The kidneys are particularly liable to be attacked in this way; indeed, one of their involvements is so serious and fatal in the tropics as to have been given a separate name, ”Blackwater fever,” from the quant.i.ties of broken-down blood which appear in and blacken the urine.
The vast majority of attacks of malaria are completely recovered from, like any other infection, but it can easily be seen what an injurious effect upon the system may be produced by successive attacks, keeping the entire body saturated with the poison; while there is serious risk of the parasite sooner or later finding some weak spot in the body,--kidney, liver, nervous system,--where its incessant battering works permanent damage.
How long the infection may lurk in the body is uncertain; certainly for months, and possibly for years. Many cases are on record which had typical chills and fever, with abundance of plasmodia in the blood, years after leaving the tropics or other malarious districts; but there is often the possibility of a recent re-infection.
Altogether, malaria is a remarkably bad citizen in any community, and its stamping-out is well worth all it costs.
CHAPTER XIV
RHEUMATISM: WHAT IT IS, AND PARTICULARLY WHAT IT ISN'T