His efforts were rewarded with success. He proved beyond every peradventure that the Anopheles mosquito is the intermediate host, and that no one can contract malaria except he be bitten by a mosquito which has previously bitten a person suffering from that disease.

In telling of his achievement, Ross declared: "The exact route of infection of this great disease, which annually slays its millions of human beings and keeps whole continents in darkness, was revealed. The minute spores enter the salivary gland of the mosquitoes and pass. with its poisonous saliva directly into the blood of man. Never in our dreams had we imagined so wonderful a tale as this.'

But even Ross little dreamed when he made his great discovery that the wonderful tale his astute mind had unfolded was to be but the beginning of a long series of related discoveries which would end entirely humanity's helplessness in the face of epidemic diseases.

The medical world had hardly ceased to wonder at the work of Ross when Reed, Carroll, and Lazear, of the U. S. Army Medical Corps, proved-Lazear at the cost of his life and Carroll at the cost of a severe spell of yellow fever that the Stegomyia mosquito plays the same role with yellow jack that the Anopheles does with malaria.

HOW MOSQUITOS, RATS, AND FLIES SPREAD

DISEASE

Then came others with their discoveries that bubonic plague is transmitted by fleas carried on rats and ground-squirrels; that sleeping sickness is carried and transmitted only by the tsetse-fly; that dengue is carried by other species of mosquitoes, and more recently that the body louse is the culprit which carries typhus from man to man.

Likewise has our increasing knowledge of the principles of the spread of typhoid fever led us to the point where the only reason we contract it is because some one has been careless with the excreta that comes from persons having typhoid in their systems. We know that milk is a frequent vehicle of infection. We know, through the researches of Dr. Howard and his associates, that the house-fly,

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which he has christened the "typhoid fly," constantly furnishes free transportation for germs that are seeking an entrance to some human system. We know how much water has to do with its dissemination, from the fact that in cities in Europe where there is a perfect water supply the number of cases is seldom above ten per hundred thousand people, and in America seldom above twenty per hundred thousand, while in cities where there is impure tap water the rate goes up to two hundred and even three hundred per hundred thousand population. come now to be accepted by sanitarians that in any average city of considerable population and ordinary sanitary regulations all sickness from typhoid fever over twenty cases per hundred thousand inhabitants is attributable to the water.

It has

How much the fly has to do with the spread of the disease is illustrated by the experience of the army encampment at Jacksonville during the Spanish-American War. The lime that was carried on the feet of the flies from the latrines to the mess-tables showed that nearly all of the hundreds of cases of typhoid that infested the camp were caused by germs carried to the food of the men from the latrines. The fly has been caught red. handed in divers instances. Some of them have been permitted to walk over infected material and then to walk over culture plates. In every case almost every point on which they set their feet brought forth a colony of typhoid germs. In other cases flies have been caught and given a bath in sterile water, with the result that a single bath has brought a hundred thousand germs from the body and legs of one fly.

THE SAD HISTORY OF "TYPHOID MARY"

There is one class of people who are a permanent menace to humanity. About 22 per cent of those who contract typhoid fever live to become germ carriers. The germs like them so well that they agree to dwell in peace and harmony with their hosts; but as they go about they spread a trail of typhoid fever. Ant illustration of this is to be had in the case of that celebrated woman, “Typhoid Mary." She had suffered an attack of

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era that they are almost as serviceable in the tropics as they are in the temperate zones. The fly carries the germ of cholera and of dysentery just as it carries the germ of typhoid. These germs use the same vehicles and travel in the same general way from the intestines of one person to the mouth of another.

TYPHOID VACCINATION

But while all sorts of prevention in the line of sanitation help to check the spread of the disease, the final blow was given to it by the discovery of the principle of inoculation for typhoid. The germs of typhoid are grown in beef broth, and when they number millions for every thimbleful of the broth they are killed by the application of heat. The dead germs are then injected into the blood with a hypordermic syringe, and three doses of these dead germs are nearly always enough to make the body immune from the invasion of live germs; perhaps because they do not like to dwell amid the sepulchers of their race.

The success of vaccination for typhoid has been remarkable. In the history of hundreds of thousands of cases only a third as many vaccinated people have contracted the disease as unvaccinated people. Furthermore, the disease terminates fatally only a third as many times with vaccinated people as with unvaccinated ones. In other words, vaccination against typhoid divides the chances of dying from the disease by twelve.

Typhoid fever, however, is not so much of a tropical scourge. It does flourish in semi-tropical countries and among white people who go to the tropics. The natives seem to be rather immune from it, mayhap because the typhoid germ refuses to dwell in the same body with ambie dysentery germs, with which so many tropical people are afflicted. But the lessons which our studies of the principles of the spread of typhoid fever have taught us fit in so beautifully in tropical

The sum of all of these discoveries is that they place in the hands of mankind the power to overcome the most terrible diseases with which the tropical world has been afflicted.

CAPITALIZING THE DISCOVERIES

And now, having looked far into the past to see the vast need there has been for such discoveries, and into recent history to learn something of how they were made, let us journey around the tropical world today and see how they are being applied.

Of course, we go first to Panama, for there they are being applied on a scale that is extensive and with a thoroughness that shows the possibilities of such application. Indeed, no factor for putting the new science of tropical medicine to the most rigid test is wanting there.

Before the United States took control and Colonel Gorgas began to apply the lessons that had been learned in Cuba, yellow fever was endemic, malaria almost universal, bubonic plague not exceptional, and smallpox not infrequent in its occurrence. Things had been so bad that they defeated the French in their efforts to dig the Panama Canal, and when the despair of the bubble-burst boom days settled like a night over the wrecked hopes of the French failure, conditions grew even worse.

Colon was a swampy mire of filth which bade warm welcome to every germ that came along, and extended hearty hospitality to every mosquito and flea that traveled that way, bidding them all to "be fruitful and multiply"-an invitation as heartily and as appreciatively accepted as it was extended.

Panama offered a haven to every disease borne upon the wings of commerce. The water-carriers who peddled water from contaminated springs became the

allies of suffering, and the result was a death rate of vast proportions. Stretching across the country between the two cities lay a vast expanse of untamed jungle and undrained swamp that was a paradise to the mosquito world. And then the masses of the people were hopelessly ignorant of all things sanitary and as careless as they were ignorant.

To add to the unlovely state of affairs, the ships that came in from South and Central America carried diseases with them. And so it was that one might look over the entire tropical world in vain for a place to put the new science to a se

verer test.

The United States was not willing to undertake the sanitation of the Canal Zone without including Panama and Colon as a part of the sanitary district, and so it was insisted that Uncle Sam should have perpetual sanitary control over the two major cities of the Isthmian republic, and Panama agreed.

After the international problems were settled Colonel Gorgas and his aides got busy. They built for Panama and Colon up-to-date sewer and water systems, the cost thereof to be returned to the United States in small annual payments. They cut down 16 million square yards of brush a year, drained a million square yards of swamps, cut 30 million square yards of grass, maintained nearly three million feet of ditches, emptied 300,000 night-soil cans and a million garbage cans, fumigated 11 million cubic feet of residential space, and did other things in proportion in the Canal Zone and in equal proportion in the two terminal cities.

THE MOSQUITO IN THE COURT OF APPEAL

For awhile the rigid methods of the Sanitary Department met with success, and the morbidity and mortality rates. both showed a remarkable decline. But then came an epidemic of yellow fever.

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The mosquito, tried and convicted in the researches of Ross and Reed, and with that sentence confirmed by the sanitary work in Cuba and elsewhere, now came to appeal to its final court for a reversal of judgment. He claimed an alibi, and he proved to the minds of thousands that he was not responsible. Hundreds tore off the screens from their houses and thousands pronounced the criminal a maligned individual. Indeed, the revulsion of sentiment went so far that men in the highest places were lining up on the side of the mosquito.

But Colonel Gorgas remained firm, and finally former Governor Magoon came upon the scene to back him up, and to give him a chance, as the counsel for the prosecution, to prove again the guilt of the accused. For three months the trial went on, and as soon as the yellow-fever mosquito was banished the epidemic terminated, and Colonel Gorgas was able to offer $50 for each yellow-fever mosquito that could be brought him. Thus for the last time in all medical history the mosquito had his day in court and was finally and forever pronounced a creature beyond the pale of the law.

Rats and mice came in for the same stern measures of repression, and the result has been that where yesterday the grim specter of death held Panama as a favorite abode, today it has to seek other regions for its preferred haunts. Where, at the beginning of our work at Panama, all the dangerous diseases in the catalogue held high carnival and gave little heed to the despair of the people, today one may see there a sort of combination between a national tropical park and an international tropical health resort.

Every possible difficulty in the way of the accomplishment of this end was encountered when the work began, and the triumph has been as inspiring as the situation seemed hopeless.

THE VICTORY OVER YELLOW JACK What the United States has done in Panama is no more than might have been expected in the light of what it had done in Cuba. There Colonel Gorgas, with the support of Gen. Leonard Wood, faced a terrible yellow-fever situation.

In

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years more than 35,000 residents of Havana alone had died of yellow jack. In a year or two yellow fever was banished from the island, bubonic plague was gotten rid of, and smallpox came under control.

The experience of Cuba and Panama has been duplicated throughout the tropical world wherever the lessons of those sanitary triumphs have been enforced with proper vigor.

Consider Brazil, which in times past had come to be regarded as the natural habitat of yellow fever. In the year following the discovery of the mosquito's part in the transmission of that disease, there were 35,000 deaths from it. The wonderful influx of young men from the outside world, the "conquistadors of a new era of commerce,' was about to be checked and the development of the great tropical republic set back for years. But Brazil would not have it so.

Rio got busy, a perennial clean-up day was ordered, and where, in its harbor, ships once had rotted because their crews had died from yellow fever and none could be secured to replace them, there soon was not a case to be found. Thus Rio, Santos, and other Brazilian cities. have become health resorts by contrast.

THE FIGHT AGAINST MALARIA

What has happened with yellow fever has not happened with malaria simply because the world does not dread it as much and will not make the thorough fight against it that has been made against yellow jack; and yet malaria has been a greater curse to humanity through more centuries than yellow fever has ever been.

Where yellow fever has slain its hundreds, malaria has slain its thousands. It has not visited mankind as a grim messenger, smiting whole nations today, and tomorrow disappearing; rather its onset has been so gentle and its reign so persistent and so general that the public mind has never been wrought to the pitch necessary to its eradication.

The fact that it results in less direct suffering and fewer proportionate direct fatalities than yellow fever has held the fears of the people in check and has permitted malaria to remain endemic in al