Dr. Lord, a scientist, allowed flies to eat sputum from a man who had tuberculosis. Those flies then deposited their flyspecks, and fifteen days later Dr. Lord examined the specks and found living tubercle bacilli in them. Those microbes of tuberculosis had been taken into the mouth of the fly, had gone safely through its body, were alive when they left the body as flyspecks, and after

CARRIES YELLOW FEVER

fifteen days they were as vigorous

as ever and ready to threaten the living tissue of human beings. Think of the flyspecks which are left on our food when flies stand upon it.

Turn also to mosquitoes. In 1793 within the space of six and a half

STEGOMYIA MOSQUITO THAT Weeks one tenth of the population of Philadelphia died of yellow fever. Naturally, of course, the city was in a panic. No one knew what started the fever nor how it traveled from one person to another. But, thanks to science once again, we now know that if every mosquito of a certain kind were banished from the earth to-day, no human being would ever again be killed by yellow fever. It has been proved that stegomyia mosquitoes are the only yellow fever agents in the world. By their sting, provided they themselves have already stung a yellow fever patient, they pass the disease along. Malaria is another

disease which is carried only by mosquitoes. A person who was never stung by the anopheles mosquito would never have malaria.

It is these facts, then, that explain the modern fight against flies and mosquitoes. We have no objection to the little creatures themselves, but we greatly object to the diseases which they may inflict upon us. We therefore do what we can to reduce their numbers. A careful housewife keeps the garbage pail closely covered, that flies may not enter and lay their eggs there. She has it emptied often and scalded, that such eggs as may have been laid on the food before it went into the pail may be killed and never allowed to hatch. She also keeps her food away from the feet of flies.

MOSQUITOES

Above is anopheles that carries malaria.

Below is culex the common, harmless

mosquito. We know which is which by the position each takes when resting

A careful city takes the same fly facts into account. It allows no piles of rubbish to stand about; it allows no dead animals to stay unburied; it insists on having clean streets and a city without places where flies may lay their eggs. All this explains the passion for clean. things which now moves all civilized people. We wish to breathe clean air in clean streets; we wish to eat

clean food where no disease microbes may be found; we wish to be rid of city waste promptly because we are not willing to run the risk of increasing danger for ourselves from microbes which might threaten us.

As for exterminating mosquitoes, this is done by filling with earth all marshy places (for it is there that mosquitoes lay their eggs) and by pouring kerosene oil over open cisterns and ponds too large to be filled. Mosquito eggs and wigglers are killed when kerosene covers the surface of the water in which they live.1

In every city the intelligence or the ignorance of the citizens decides what their own life and death prospects shall be.

1 See Town and City for an account of the war against mosquitoes in New Orleans.

CHAPTER XXXII

SPREAD OF EPIDEMICS

A certain boy in New York City had measles. He was quite ill, went to bed, called the doctor, stayed at home for some time, then was well again and went back to school. After that he became very popular. Why? Because, as Mr. Riis says, “He could pull the skin off with his fingers as one would skin a cat." And he gave the largest rolls to his dearest friends. He did not know and his friends did not know that microbes of measles are thick in each smallest fragment of skin that comes from any one who has had the measles. So the skin went from the boy to his friends. They took it home with them and divided it among their other friends.

Then came the climax of that bit of ignorance. A great epidemic of measles broke out wherever the skin had been distributed. Many were ill; some died; all suffered. If those boys, their parents, and their friends had known the facts about measles, they would have used their brains and saved their bodies from a very preventable epidemic.

The truth is, that when we say "There is an epidemic in this place or that," we simply mean that disease

microbes of one sort or another are passing rapidly from person to person, and that many have already been overcome by them. It is evident, then, that the life and death record of every village and city in the land must depend largely on what young people as well as old people know about disease microbes, and on what school children as well as doctors are willing to do to keep the microbes from spreading.

But there is another contagious disease which is far worse than measles. In the year 1854 this disease broke out on Ponape, one of the Micronesian islands. It came from the garments of a sailor who had died there of smallpox. At the time of his death Ponape had a popu lation of ten thousand; but six months later half those ignorant islanders were dead and buried. The microbe of smallpox had slain them before they had time to learn how to protect themselves from this preventable disease.'

In former times people dreaded smallpox and fled from it. They knew it was contagious and realized what its results were; but they tried in vain to escape it. Though they fled they were overtaken by it; they suf fered from it and carried the marks of it on their faces until they died. They were also killed by it by the hundred thousand every year. According to a careful calcu lation fifty million Europeans died of smallpox between the years 1700 and 1800.

1 A full account of this is given in Town and City.