dust, when we breathe dirty air. Some come in dirty water. Some, a
great many, come in dirty food, on lettuce and celery that have been
carelessly washed, and especially in dirty milk. Some of the worst
of all among them, the germs of typhoid fever, are carried on the
feet of the common house fly, and planted all over the things that
we are going to eat. Rats and mice also carry diseases—in their fur,
on their feet, or even in their blood. So, too, do certain stinging,
biting, and sucking insects; and when they bite or sting or suck the
blood of some larger creature, they plant the seed of some disease
in his body, where it grows and flourishes until the animal sickens
and perhaps dies. No one, for example, ever catches yellow fever or
malaria unless he has been stung by a mosquito which has already
bitten somebody else with the disease. The mosquito picks up some of
these living germs in the blood of one person, and sows them in the
blood of the next; just as one might take seed from one field or
garden plot and sow it in another.
All the catching diseases, then, from ordinary colds to pneumonia,
and from measles and chicken pox to typhoid and scarlet fevers, are
nothing in the world but living plants or animals growing in our
bodies and poisoning us. We say that we catch the disease. Really
the disease catches us. The disease is a living thing, that in very
real sense, hunts for us, and catches us as a lion or a bear might
do, or a poisonous snake. If we could kill these lions, bears,
poisonous serpents, bacteria, and the rest, why then they wouldn’t
get a chance to kill us. Then we should all live to old age—unless
we poisoned ourselves, as I am sure some persons are quite foolish
enough to do, or met with some accident that we could not help. But
of course there are a few other diseases, like rheumatism and heart
disease and indigestion, where the trouble may be with ourselves and
not with any other living creature that gets after us.
Just to show you how one of these living, catching diseases manages
to get on, and when one victim dies, changes over to another, I am
going to tell you about something that I am sure you have already
heard of either in your history, or else in stories that you have
read about the Middle Ages, when the knights wore armor and the
yeoman fought with spears and bows.
In those good old times, every little while, whole cities would be
smitten with a terrible disease called the plague. Perhaps you
already know about the Great Plague of London in 1665, when seventy
thousand people perished, and the dead lay in the streets because
the living were too few to bury them. The same man who wrote the
story of Robinson Crusoe, wrote also a story of this great plague,
not a pleasant story, naturally, but one that you will want to read
later when you are older.
The trouble was nothing in the world but dirt and rats. The rats
lived in the dirt; and the minute, living plant that makes the
plague, lived in the blood of the rats. From them it got into the
blood of human beings. But so long as a city kept clean and free
from rats, it never had the plague. But when it let itself get
dirty, as ancient cities usually did, then it might lose a fifth of
its inhabitants in a few months.
As people, therefore, began to be more decent, the plague began to
disappear; and after about the time of our Revolutionary War, most
of Europe had become so clean and civilized that they had no more
plague there. But still it lingers in other parts of the world,
where there is more dirt, and where people, instead of putting their
waste tidily away in the bucket or burning it up, throw it out the
back door for rats to eat. Always, even now, the plague threatens
Asia. During the first ten years of this very civilized twentieth
century five million persons died of it in India alone.
And all because of dirt and rats and fleas. The rat lives in the
dirt. The fleas live on the rat, and when they bite the rat, get a
stomachful of blood, and with it some five thousand or so of the
little plants that cause the plague. Then the flea jumps off the
rat, on to a man, and bites him. Then a few of these five thousand
germs get into the man’s blood. By the next day, these few have
become millions. Within a week, often within two days, the man is
dead—simply poisoned. But if the man had kept his house clear of
rats and his skin clear of fleas, by keeping them both clean, he
would not have been poisoned at all.
I am sorry to say that since the year 1900, and even as late as
1909, there have been cases of the plague in one or two especially
dirty cities in the United States. So the National Government had to
interfere, to make them clean up and get rid of their rats.
Otherwise we might have had a terrible time; while as it was, some
three hundred people died—which is more human beings than most of us
know by name.
But you can’t have the plague without rats, and you can’t have rats
without dirt. So, therefore, every civilized government in the world
keeps men at work in its seaports, killing the rats that come in the
ships, lest they bring the plague from China or India, where they
don’t mind a little dirt.
There is another animal, dirtier even than the rat, and on the whole
rather more dangerous—and that is the fly. Wherever there is dirt,
there are pretty sure to be the germs of various diseases. If there
is anything the fly likes, it is dirt. He eats it; he wallows in it.
The dirt sticks to his feet, and the disease germs stick to the
dirt; for a fly is not nearly so much smaller than an elephant as a
disease germ is smaller than a fly.
Then the fly tracks over our food or falls into our milk. He may
carry a million germs on his body, and every time he puts down one
of his six feet he plants at least one. In forty-eight hours this
single one may have grown to sixteen thousand. Then some boy or girl
eats the food and is sick; or some baby drinks the milk and dies.
XLI
The Great War
The hardest battle we have to fight is with these living diseases.
They kill more people in each year than have perished at the hands
of the enemy in all the wars we have ever fought. During our war
with Spain, the flies alone killed in camp four times as many of our
soldiers as the Spaniards killed in battle. Every day of our lives
in war and in peace, we are fighting for our lives against these
unseen foes of pestilence and disease.
This is how we carry on the campaign. Our first line of defense is
keeping clean. Every city now-a-days has men who watch its water
supply. The surroundings of its ponds and reservoirs are carefully
guarded. If necessary, the water is filtered before it goes into the
street pipes. Always, if the city is half civilized, it filters all
its sewage before turning it into the rivers. Thus, if there are any
living animals or plants in the water, they get strained out. In
many houses, where the people are especially careful, they strain or
filter the water once more, or boil it till they kill every living
creature therein.
Then every city has other men to look after its milk. Because milk,
being good food for us, is good food also for other living
creatures; so that if one single germ gets into a bottle, it will
shortly grow to many millions, and play sad havoc with the family
that uses it. Careful people, too, do not depend on the city to keep
their milk clean, but see for themselves where it comes from;
especially if there are children, for children not only drink much
milk, but are peculiarly liable to catch the diseases which come in
it.
Careful people, in addition, look out that all their food is clean.
They see that none has been kept out where dust may fall in it,
where rats or mice may brush against it, or where flies may track
over it. In all these ways, the seeds of diseases may get sown in
our food. One ought to make sure that there are no rats, mice, or
flies in the house at all; and one ought to make sure also that all
raw foods, like lettuce and celery are thoroly washed, for these
often carry the eggs of certain animals, living eggs which will
hatch out inside anybody who swallows them, and not be at all to his
advantage.
That, then, is our first line of defense—keeping our food clean,
lest the enemy enter through our mouths. Our second defense is to
keep the air we breathe, clean and fresh and dust free, lest the
enemy attack us by way of our lungs, and we die of pneumonia or
consumption, or sicken of common colds and the grip. In all this, we
are like a country with a powerful navy which can prevent the enemy
from making a landing on its coast. So long as we keep these minute
foes out of our houses, and still more so long as we keep them out
of our cities, they cannot get near enough to us to do us any harm.
But when the enemy has broken through our first line of defense, and
begun to lay siege to our bodies, we still have a second line of
fortifications to protect us. One thing our skins are for is to stop
germs. So long as we keep a whole skin, it is pretty hard for many
sorts of germs to gain an entrance. And where the skin is thin, as
it is inside the mouth and nose, there is always a somewhat thick
and sticky mucous to catch the germs; while the eye has tears to
wash them out. We are like fortified cities; and we must not let the
enemy make a breach in the wall.
So we must be careful not to neglect even small cuts, sores,
scratches, and the like, thru which the foe can enter. People
sometimes get most loathsome and dreadful diseases by drinking from
dirty cups when the skin of their lips is cracked in cold weather;
while the little plant that causes blood poisoning, often gets in by
way of a cut so small as to be hardly noticed. No child would ever
die of lockjaw, if he did not first cut or blow a hole in his skin.
Strangely enough, a great many of the lesser catching diseases of
children, measles and colds and the like, make their way into the
blood because of holes in the teeth. A hollow in a tooth gets filled
with food. A germ or two finds its way into this food, and grows
there till it becomes many millions. So naturally, an assault by an
army is more likely to be successful than an assault by a mere
handful. Merely by keeping the teeth and mouth clean, and by having
a dentist stop the holes in the teeth, one can cut down to less than
half, the number of days’ sickness in a year. Some people go beyond
this, and always after they have been in dust or bad air, wash out
their noses with some fluid that will dispose of any of the enemy
who have lodged there. In fact, people who have suffered almost
continually from colds and grin are sometimes cured at once and
completely, by merely a slight operation on the nose, which opens up
to the fresh air some hollow in which the besieging hosts were wont
to lurk.
Our second line of defense, then, is keeping skin and teeth and nose
clean and whole, that the enemy may have no place wherein to hide,
and no breach through which to enter. If this gives way, then we
must engage the enemy hand to hand.
Then it gets to be a pretty even thing between us. The invaders try
to poison us, and we try to poison them. We form an acid in our
stomachs—the same acid, by the way, that tin-men use to solder with;
one can buy it anywhere. Regularly, we use this to digest meat with;
but if any living things get into our stomachs, we give them a dose
of this acid, and usually bowl them over.
If they get by this, we poison them with bile. The bile is made in
that most useful organ, the liver, and is partly waste matter, more
or less hurtful to the body, which we are getting rid of. So since
we don’t want it to poison us, we use it to poison other living
creatures inside us.
That, then, is our third line of defense. If the enemy gets by that,
then the war has to be fought out in the blood. Even if we win, we
shall suffer damage, and very likely take to our beds and have to
call on the doctor for reinforcements.
The blood itself, good healthy blood, that is, will poison the
germs; for the blood of any sort of creature, as I have explained,
will poison any other sort. Besides that, we manufacture special
poisons with which to combat each special creature that makes a
special poison to assault us. So each side poisons the other, and
the battle becomes a question of which can kill the other first. In
one case, we are sick and recover; in the other case, we are sick
and die.
When the doctor takes a hand in the battle, he begins by giving us
food and medicine, to make us strong for the war. Sometimes, besides
these, he gives us something which, while it harms us a little,
harms the enemy a great deal more. In a few cases now-a-days, he
pumps into our bodies some of the blood of another animal, generally
a horse, which has been fighting the same disease, and so has its
hand in and can manufacture many times as much stuff to kill the
germs as we can. Many, many people have been saved by this means,
who otherwise would certainly have died.
In a few cases, too, small-pox especially, by means of vaccination,
long before the enemy attacks us, we can be loaded up with
ammunition to repel the invader when it does come. The vaccination
gives a mild form of the disease (not so very mild perhaps you
think, when your vaccinated arm gets nice and red); we defeat this
triumphantly, but we manufacture so much “anti-toxin” to do it with,
that for years afterwards we are all ready for the first germ that
shows its face in our blood, and slay him before he gets a chance at
us. The “anti-toxin,” as you know, is the substance which we make
with which to get back at the germs that are trying to poison us
with the “toxin” which they make.
But even the battle in the blood is not fought quite in the open. We
have, so to say, breastworks and rifle pits, where we can still make
a stand, even after the invaders have gained a footing in our
bodies.
Perhaps you have sometimes felt small roundish hard bunches as big
as a pea or a marble, under the skin at the side of the neck, under
the arm pit, or in the groin. Sometimes these swell up and get sore.
These nodules are the lymph glands. They surround the passages
through the flesh along which the invading germs are likely to come,
after they have burst through the skin. They are then like the
fortifications along a road over which the enemy is likely to march.
We can feel them only in certain places; but they are all over the
body, under the skin, and beneath the membranes of the lungs and the
digestive organs, wherever the body is most open to attack.
The garrison of these little forts are a peculiar sort of naked
cells, which having no walls or covering to hold them in, can change
their shape, reach out, and draw back again, as if they were
sea-anemones or polyps or some other sort of water creature, and not
part of our bodies at all. These cells are twenty or more times
larger than the bacteria. And when the bacteria or other germs come
along through the passages of the body on their way to the blood
vessels, these guardian cells of ours reach out and grab them, drag
them in, and devour them, like ogres that devour travelers who go by
their castles, over the high road. Only in this case, our sympathy
must be entirely on the side of the ogres.
But these lymph cells do not always stay in the lymph glands. When
they like, they let go their anchorage, and go floating off through
the blood, or through the lymph; for the lymph is only the watery
part of the blood without the red corpuscles, which doesn’t stay in
the blood vessels but soaks everywhere through the body, feeding and
moistening the cells. These lymph cells, or white blood corpuscles,
can go everywhere over the body, pushing and squeezing and elbowing
their way among the other cells or traveling in the open spaces
between them.
When the enemy enters the body, and begins to poison the blood, the
white corpuscles smell them, and at once begin to crawl toward the
smell, to reinforce their brothers in the particular lymph glands
which happen to be at the point of attack. You get a sliver in your
finger. The sliver opens a hole in your defense, and carries in some
hostile germs. If, therefore, your lymph cells did not come to the
rescue, you would inevitably die of blood poisoning. But they do
come to the rescue. The white “matter” or “pus,” which in a few days
comes out of the wound, is in large part the dead bodies of the
fallen enemy and of the defenders who have perished in the fight. So
in general, the invasion is stopped at the first lymph gland. A few
thousand white corpuscles fall in the war. The enemy is massacred to
the last man. And the body is saved.
Or else the foe get the upper hand; increase faster than the
defenders can kill them off; break through the defense; enter the
blood stream; invade the whole body; overrun the country; and put
the inhabitants to the sword.
[Illustration: Lymph Cells or White Blood Corpuscles]
All our lives long, every day of our lives, we keep up this fight
against disease. When measles does not threaten us, then it is
colds. The game, therefore, is to strengthen our outer defenses, by
keeping our food and houses clean, and our skins and teeth, and the
air we breathe. And while we are doing that, we ought also to keep
our bodies strong and resistant, with proper food and exercise and
sleep, ready to put up a good fight if the enemy should break in. We
know so much now about the causes of disease, that being sick or
keeping well is a good deal under our own control.
XLII
More About The Great War
We are not the only creatures who have to fight for our lives, every
day of them, against an ever-present but unseen enemy. All other
animals have to do the same, if they are big enough for any thing
else to live inside them. There are parts of this earth where no
cattle or horses can live, and where all the heavy work has to be by
machinery or by hand, because there are flies there which bite all
the larger animals, both wild and tame, and plant germs in their
blood. After that the tamed creatures, at least, almost invariably
die.
Animals, therefore, have their catching diseases just as we have.
Sometimes they are the same as ours; more often they are
different—things that dogs or cats or horses catch, and we do not.
Once, I remember, it must have been more than sixty years ago, all
the horses over entire states suddenly fell sick. One hardly saw a
horse on the street or anywhere; and because that was long before
the days of automobiles or trolley cars, people had to walk or to
drive oxen, and sometimes even to harness up cows. But after a few
months, the horses all either died or got well again. Those that got
well had their white blood corpuscles trained to fight that
particular germ; so there was no more serious trouble. But it would
make you laugh to see a span of cows haul a milk wagon.
There is a distemper that kills puppies. There is a chicken cholera
which wipes out whole flocks of hens. The monkeys in the menageries
succumb to colds and consumption, which they catch from the people
who come to look at them. When the plague enters a city, the cattle
and the various small animals of the house begin to die first before
the human beings, and thus often give them warning, and time to
flee. In all cases, some particular living and growing thing breaks
through into the blood, or gets a foothold somewhere in the body,
and begins to poison it. Then the invaders and the blood cells fight
it out—and the best man wins.
There is a disease called anthrax which attacks various animals,
ourselves and the birds among the number. A hen, for example,
fighting anthrax, will almost always win, if it is kept warm. The
lymph cells fight better when the blood is hot. But if the hen’s
feet are kept in cold water, then the anthrax wins. The cool blood
gives it the advantage.
That is how we and all other creatures catch cold. Mere cold would
never give us chills or grip or colds. But our being chilled, or
getting our feet wet, or sitting in a draught, just cools down some
part of the body enough so that the blood cells can’t fight quite so
well. Perhaps it is only for a moment; but in that moment the enemy
gets its footing. Some people say that the reason why a dog’s nose
gets hot when he is sick, and why human beings and animals have
fever when they have anything catching, is so that their bodies may
be well warmed up, and their lymph cells may do their fighting in
hot blood.
Nor is it only for human beings and animals that all these catching
things lie in wait. Plants have their troubles as well. Perhaps you
have noticed on wild cherry trees growing by the roadside, or on
plumb trees, that sometimes almost every tree in a clump, and even
every branch on a tree, will have a hard black lump, as large as
your fist, growing out of the bark. The tree is sick; sick with a
patching disease of trees called the black knot.
The disease itself is something like a mold. It breaks through at
the growing tip of the branch where the bark is new and thin. Thence
it grows down the branch sucking up the living substance of the
plant and killing everything as it goes. The “black knots” are the
fruiting of the invading plant, where it has broken through the bark
and is growing fine dust-like “spores,” which are its seeds and will
spread the trouble to neighboring trees. When a tree comes down with
this trouble, the only thing to do is to cut off every diseased
branch a foot or more below the lowest knot, and burn it up.
Possibly then, we may get ahead of the enemy, and so save the rest
of the tree.
Almost every cultivated plant has its diseases. The brown spots on
leaves and fruit of a pear tree are the plant’s measles. The hard
lumps in an apple are its mumps. There is a sort of black
scarlet fever of wheat, rust it is called, which destroys a million
dollars’ worth of grain each year. Some plants look wilted because
they need water; some, because they are sick and need medicine.
And they get medicine, too. Sometimes the plant-doctor gives it by
soaking the seeds in the remedy; sometimes by spraying it on the
leaves with a pump and a hose. In any case, the medicine is some
sort of poison that kills the living creature that makes the
disease, but does no special harm to the cultivated plant.
We even speak now of diseases of soils. Because there are minute
animals that get into soil and lessen its fertility so that no plant
will do well in it. Green-house keepers often bake their earth
before setting out plants in it, in order to cure it of any disease
that it may have caught while the last crop was growing; while a
healthy soil will catch a disease from a sick one, exactly as a
healthy animal or plant will do.
The fact that most diseases of men, animals, plants, timber, and
soils are living things is something that has not been known many
years. Indeed, it is only since the twentieth century came in, that
we have really made much of a start at finding out just what plant
or animal is responsible for the sickness of any other. It is only a
question of time, probably a few centuries at the outside, before we
shall have killed off all the common diseases. Then nobody can
possibly catch anything any more—measles, mumps, chicken pox, colds,
grip, diphtheria, scarlet fever, or anything else. There will not be
anything left to catch; and nobody will be sick any more, unless he
eats more than is good for him, or does something else that he might
just as well not have done.
XLIII
Living Apothecary Shops
Not only are the bodies of all except the very smallest animals and
plants at the same time gas engines and battlegrounds; they are also
living apothecary shops. Indeed, it is a pretty well stocked drug
store that has more different chemicals in it than a man and his
horse, and his dog, and the garden that he works in, all together,
manufacture every day of their lives.
Think to begin with, of all the different perfumes of all the
different flowers, and all the various tastes of all the different
vegetables which we eat, and of all the various spices and herbs
which we use for flavorings in our food. Think of all the different
coloring matters in flowers and leaves. Think of the tar, rosin,
pitch, maple syrup, turpentine, gum, varnish, shelac, india rubber,
tan bark, and the rest, that we get from a few trees alone. The
chemicals made by even the ordinary plants could fit out the shelves
of a fair-sized drug store.