CHAPTER XXXI

PULLING THE TEETH OF THE TROPICS

Of all the sights on the Canal Zone there is none more worthy of note than a dilapidated galvanized iron ash-can in the hills back of Paraiso.

Half an hour's stiff climb from the village will bring you to where it stands in a little hollow in the side of the mountain. If you look up hill, you see a dense wall of tropical jungle. It is a tangle of unbelievable vegetation-a felt-like fabric of green; palms, mahogany, cocobolo, and lignum-vitæ for the woof, and countless varieties of vines and creepers, great ferns, and many-branched grasses for the web. It is embroidered with bizarre patterns in scarlet and yellow blossoms and ghostly orchids. It takes a sharp machete and a strong arm to penetrate it. It stands there untouched by civilization-primeval-just as it stood when Balboa tore his way through it to fame four centuries ago. The life which spawns within its dense shade is not only vegetable. Strange beasts are there-tapirs, sloths, iguana, the giant lizard, and snakes. It is the home of the boa, and many lesser but more venomous breeds. More innumerable even than the varieties of plants are the species of insects. With acute ears you will hear the faint murmur of their life, the never-ceasing rustle of myriad microscopic feet on the rotting leaves; of myriad minute and filmy wings beating the dead, sodden air. The tropical jungle has a sinister aspect, an evident menace, which is unknown in the North.

Turn about, and you will look down into and across the

valley of the Rio Grande. In the bottom is a haze of murky smoke, shot through with flashes of white steam. Through rifts in those man-made clouds you get glimpses of rushing dirt trains, of straining monsters of steam and steel, of an army of active, hurrying men. The clang of iron on iron, the shriek of steam-whistles, perhaps the roar of a dynamite blast, beat up against your ears. On the sides of the hills you see villages-clusters of homes, wellkept lawns where all that is beautiful in the jungle has been separated from what is noxious and brought under cultivation: noble groups of palms, red and yellow and green shrubbery, flaming bushes of hibiscus; you see mothers in crisp white dresses playing with their babies; and if it chances to be the right hour, you will see a rout of children, as husky youngsters as you could find in East Orange, tumble out of the school-house.

Now look down at your feet. Two or three little threads of water trickle down the sides of the hollow in the hill where you are standing and join forces in a little brook. The hand of man is as evident here as in the bottom of the valley. All the vegetation is close cropped on either side the rivulet— the jungle has been pushed back several yards. The banks of the little stream are no longer covered with dense moss and fern, as they were when the Spaniards came as they were thirty years ago when the French started a colony in Paraiso. They are black and barren-smeared with unsightly grime. Just at the spot where the three threads of water join there is a rough plank across, and on it the ash-can. Just such an unattractive affair as the men of the Street Cleaning Department empty into their carts every morning in New York City. Only this one is uglier still, as it, like the banks of the stream, is smeared with the black oil. A piece of lampwick hangs out near the bottom, and from it there falls every few seconds a drop of the blackness. Splashing into the

water, it spreads out-wider and wider, till it touches each bank-into an iridescent film. It looks like the stuff they use for oiling automobile roads. It is a compound of crude carbolic acid, resin, and caustic soda, called larvacide. These disreputable-looking ash-cans-there are many of them all through the hills at the head-waters of each stream -have a very intimate connection with the mighty work down in the valley and with the healthy bloom on the cheeks of those village children. They are outposts-frontier stations in the war against the mosquito.

As is the case in most great discoveries, there are several claimants to the honor of having propounded the mosquito theory. Our doctors give the credit to Dr. Ronald Ross, a Scotchman in the Indian Civil Service. Thirteen or fourteen years ago he carried on his very valuable experiments. However, some Italians were close on his heels. And once the theory was published, investigators sprang up on all sides who claimed to have been working on the idea these many years.

Reduced to its simplest terms, this theory is that certain diseases are transmitted by, and only by, the bite of mosquitoes. Ross worked this out for malaria, demonstrating it first on birds, then on man. This fever is caused by the presence of bacteria in the blood. These minute organisms go through the ordinary cycle of birth, mating, and death. If a female of certain species of mosquitoes (Anopheline) bites a human being at the period when the malarial germs are mating in his blood, she sucks in some of them along with the blood. After they have developed within for nine days, she becomes infectious and, if she bites another human being, inoculates him with malaria.

The demonstration of these facts gave a new impetus to the study of entomology. It was soon discovered that other diseases are spread in much the same way. The story of

how our army commission in Cuba worked out the connection of another brand of mosquitoes (the Stegomyia) with yellow fever, and how some of them voluntarily had themselves infected and died to prove the theory, has been so often told that it needs no repeating here. It soon developed that mosquitoes were not the only offenders: the sleeping sickness of Africa was traced to a biting fly, and the bubonic plague is now known to be spread by fleas who have gathered the virus from infected rats.

It would be invidious to try to determine what nation has contributed most to this new knowledge-a so vital part of modern sanitation. All over the world observers have gathered data, until to-day the credit of it, as well as its value, is truly international. But certainly we in the Canal Zone have gone the furthest in the practical application of that knowledge. Our men have been especially prepared for this job by their own experience and that of their colleagues in Cuba and the Philippines.

At first relatively little was known about the varieties and habits of mosquitoes; an immense amount of information is now at hand. Our men have collected and studied over fifty varieties on the Canal Zone. And Mr. A. H. Jenning, the Entomologist of the Commission, can give you interesting gossip about all of them-how they court and how they are born, and what they eat at three days old, and what dessert they prefer after two weeks, how and where the mother lays her eggs, and so forth. Of these fifty-odd varieties eleven species are Anopheline—all of which are under suspicion as malaria-bearers. The three commonest species are the Anopheles albimanus, A. pseudopunctipennis, and A. malefactor. The white-handed variety is known to be the most active in spreading disease. There is no direct evidence against the A. malefactor, despite his ill-sounding

name.

Of the albimanus, the most dangerous, as is true of other species, the female alone bites. She does it because a meal of blood facilities the development of her eggs. It is doubtful if she can lay without having gorged herself. She seems to prefer red blood. But she has been caught in the act of biting reptiles, and even fish. This duty attended to, she begins a search for a suitable place to deposit her eggs. More study has been given to this phase of her life than any other, and Mr. Jennings can tell you just what she will do and just what she won't in this matter. She prefers stationary or slow-moving water, well screened from the sun, where there is plenty of green scum for the youngsters to feed on. The swampy pools, such as the jungle abounds in, seem to be her ideal. The eggs in due course of time hatch out into tiny tadpolish larvæ. They spend their time feeding and breathing. Every two minutes they have to come up to the surface to get fresh air. This, as we shall see later, is the fatal weakness-the Achilles heel-in their scheme of life. Having passed safely through their larval stage, they hatch out into full-fledged mosquitoes. They mate, the female starts out after blood, and the cycle has recommenced.

An adult mosquito is a lively proposition to deal with— almost as elusive as a flea. So our sanitary men try to get them before they mature.

First

The fight against malaria falls into three divisions. of all, our men try to reduce the number of places where the female can lay her eggs. In a dry Northern climate it might be possible to eliminate such places. But nine months out of the twelve it rains down here nearly every day. And if a cow leaves a deep foot-print in the soggy ground, a couple of inches of water will ooze into it, and behold! a very fine place for Anopheline to breed. The main work of this division is in draining and filling swampy ground. Also they

the underbrush and grass in the neighborhood of settle