bread and potatoes and the rest of our food finally gets changed
over into a sort of sugar; and is as sugar, packed away in the cells
of our muscles and other tissues, mixed with the oxygen of the air,
and made ready to explode when the signal through the nerve touches
it off. The food is taken apart and put together again, combined and
separated, stored up when it isn’t needed, and used sometimes in one
way and sometimes in another. Different animals treat their food
differently after they get it swallowed; even different human
beings, eating the same food, do not always handle it quite the same
way.
Most of us take our food into our stomachs, but the earthworm crawls
through the earth, and at the same time lets a stream of earth crawl
through him, digesting what is food and leaving the rest behind as
he moves along. Amoebas sometimes flow round little water plants
many times longer than themselves, crawl along the stem, with the
stem sticking out front and back, and digest the juices as they go
along. The star-fish, which lives on oysters larger than himself,
turns his stomach inside out, sticks it into the oyster’s shell; and
after he has digested the oyster, pulls his stomach back again. A
dog will digest bones; and a cow will digest wood; while a fish will
swallow another fish nearly as long as himself, keep the tail, still
unswallowed, in his mouth while he digests off the head, and than
moves his meal up another notch.
There are all sorts of queer freaks, but the main point is that, in
the end, all our food gets built into the cells of our bodies; much
of it in the form of sugar, and that this sugar explodes as if it
were the gasoline vapor in a gas engine that some man has made. With
the force of these explosions, the body does its work; it keeps
itself warm with the waste heat.
XXXVII
Men In Glass Boxes
One curious thing about these explosion engines of ours is that,
when all goes well with our little insides, we get just exactly the
same amount of work out of each mouthful of our food, that we should
get, if we should dry the food, grind it to fine dust, and explode
the dust mixed with air in the cylinder of an automobile—as it would
be quite possible to do, if one wanted to take the trouble.
In fact, the United States Government, for several years, set people
to trying just this very thing, by way of finding out how much work
can be got out of various sorts of food, and out of which sorts a
man can get most for his money. They have a big glass box, as large
as a state-room on a steamer, with a bed in it and a table and
chairs, and also a stationary bicycle, on which one can ride without
moving, and so get his exercise. They put a man in this box, and
keep him there for a week. They weight carefully everything that he
eats and drinks; and each time he takes a meal they find out, by
drying some of the food and burning it and measuring the heat they
get from the burning, just how much that food is worth as fuel. Thus
they know how much exploding he ought to be able to do in his tiny
cylinders.
Then in addition, they keep track of all the air that goes into the
glass box, and find out just how much oxygen he uses up to explode
the food. They see also how much he heats up the air which comes out
of the box by the warmth of his breath, the heat of his body, and
the friction of the stationary bicycle when he exercises.
It always turns out that the man makes just as much heat out of the
food he eats as the same food would yield if dried and burned; and
that it takes just as much air to explode it in his body as it would
take to burn it in a stove. So the body is really an engine. It uses
up fuel like any engine; and gets the same amount of heat or work
out of its fuel as any other well-made engine would.
As a result of these experiments, and others like them, the United
States Department of Agriculture has issued a pamphlet, called
Bulletin Number 28, which tells, among other things, how much work
one ought to be able to do on one pound of almost any sort of food
that any civilized human being would ever think of eating. I trust
that every girl who reads this book, before she grows up, and goes
to keeping house, and has to feed a family, will get this little
pamphlet, or something else like it, and study carefully what
different foods are really good for. According to the United States
Government, a child can do more hard playing, and a man more hard
work, on one pound of bread, spread with four ounces of butter, than
eight pounds of broiled spring chicken; while ordinary dry crackers
and cookies are twice as nutritious as lean meat, and six times more
nutritious than oysters, lobster, and most sorts of fish.
Still, there is this most important difference between our living
engines and the engines which we build of brass and steel. When a
part wears out or breaks in an automobile, if it cannot be mended,
it has to be thrown away. But in the body, when a part of the
life-jelly wears out, as it is continually doing, we not only make
some new to take its place, but we use up the old stuff as fuel to
drive the engine.
In short then, some automobiles are built of steel and leather and
brass and rubber, and burn gasoline. And some are built of
life-jelly and burn sugar. The first sort, when it wears out, we
mend with more steel and leather and brass and rubber. The second
sort, when it wears out, we mend with more life-jelly, which we get
from the portion of our food that is neither sugar nor starch nor
oil, but the once living jelly of other plants and animals, which I
am sorry to say, we have to kill to get stuff for our own repairs.
The plants can make their life-jelly out of the air that they take
in thru their leaves and the water that comes in through their
roots. But we animals, from the least to the greatest, can get it
only by taking it away from something else. For my part, I feel
easier in my mind when I take away this life-stuff from some plant
like wheat or corn, than when I rob some breathing animal like
myself.
XXXVIII
Of Sugar and Other Poisons
Our bodies, therefore, and the bodies of all other animals, are gas
engines, which burn sugar by exploding it mixed with air. Most of
our food, to be sure, isn’t sugar, but bread and potatoes and
cookies and all sorts of nice things made of butter and flour, milk
and the like. But as I have already pointed out, the most important
portion of this food is either made over into our own life-jelly, or
else it is changed into sugar and exploded in our muscles.
Sometimes when the automobile goes by, one of the things you notice
is a very bad smell. This is largely the unburned and half burned
gasoline. Gasoline, when it burns clean, changes to water and to the
odorless and slightly tangy gas which we get in soda water, carbon
dioxid as it is called. When you burn gasoline, then, you get the
same products as if you boiled plain soda water.
Most things that burn, likewise, burn to carbon dioxid and water.
Wood does it, and coal, all kinds of oil that we burn in lamps, and
the gas that we burn for light and heat. So, too, do all sorts of
candles—paraffin, for example, or wax; and so, too, do the old
fashioned tallow candles which our great-grandmothers used to make.
Tallow, however, is a fat, except for its taste, like the fat we
eat. Practically, we eat nothing that we cannot also burn, when
dry—tho we do burn a good deal that we cannot eat.
Most of these burnable foods explode in the body, a good deal as
they burn outside. They form carbon dioxid and water—when you “see
your breath” on a cold day, you merely see the water in it that came
from your exploding muscles. If you eat largely only plain wholesome
foods, bread and butter, fresh vegetables, fruit, candy and cookies
and crackers, and all the various other foods that burn clean, they
will burn clear in your bodies, and you will yourselves be clean and
sweet as children ought to be. But if you have a taste for things
you ought not to have, and get them, then instead of good clean
water and carbon dioxid, you will explode to a lot of unwholesome,
poisonous, and smelly things, that are not at all nice outside the
body, and are still worse inside.
Unfortunately, we cannot live altogether on these clean-burning fats
and starches and sugars, which explode to carbon dioxid and water,
and leave nothing more behind than a wax candle when it burns. We
can’t make our life-jelly out of these foods. So we have to eat
also, eggs and milk and cheese and beans and peas and meat and fish,
some parts of which we can build to our life-jelly. But only about a
tenth part of our food needs to be of any of these life-jelly-making
sorts. The other nine-tenths should be the clean-burning things with
which we do most of our work and play.
But whatever the fuel with which we run our bodily engines, sooner
or later it gets used up and the waste products have to be blown off
into the air. Insects and automobiles, which take the air pretty
directly into their cells, blow off their waste gases directly into
the air again. The lowly creatures which breath the air in the
water, send their carbon dioxid back into the water again. But we
who have blood, use that to carry off our exploded sugar and other
things.
The water of the burned up food is simply added to the watery part
of the blood. The carbon dioxid becomes in the blood ordinary
cooking soda; the blood carries the soda to the lungs, and there it
changes to carbon dioxid again, exactly as it does when, as cooking
soda, or baking powder, you add it to flour and use it to raise
cake. Finally it comes out of the lungs with the breath, and that is
the end of it so far as we are concerned.
Still, we are not through with it yet; because the plants take in
thru their leaves the carbon dioxid that we animals breath out thru
our lungs, take it apart again, mix it up with water and other
things which they get thru their roots, and finally make it over
into wood, and into starch and sugar and the like which we animals
eat up once more. So if we eat the plants, the plants also eat us;
and the same stuff keeps getting used over and over again. And a
mighty convenient arrangement it is, too, since there is precious
little stuff to make living things out of in the world at best. Most
of the earth is just rocks.
However, I started to tell you something about the burnt up food and
exploded muscle-sugar, While it is still in the body, before blood
and lungs and skin and kidneys have combined to carry it away.
Did you ever stop to think why you are sleepy when night comes? You
play hard all day, running about until your legs are tired enough to
drop off. By and by, you begin to be sleepy, an hour or two it may
be before your proper bed time. You are tired in your legs. But you
are sleepy in your eyes. Your legs are not sleepy in the least; and
your eyes are not tired. How did the eyes find out that the legs had
been running hard and needed sleep?
It is these same waste matters in the blood. We run our legs off by
day; and by night time a hundred thousand little explosions in our
muscles have used up so much sugar and the rest, that the blood is
filled with the waste material, and the lungs cannot carry it off.
So it stays in the blood and poisons us—not badly, but just about as
much as if we had taken a small dose of laudanum or alcohol or any
of the large number of sleepy poisons, which kill one by putting him
to sleep so hard that he cannot wake up. Our “fatigue toxins” as we
call them (which is simply Latin for poisons that we make by getting
tired) poison us just enough to make us sleep. While we sleep we
don’t do much; less of these toxins are formed; the lungs and
kidneys have time to catch up with their work; pretty soon the blood
is clear again, and we wake up in the morning ready to do it all
over once more. We are made to stand a certain amount of poisoning,
and get over it. The trouble comes when we poison ourselves With
things that we put into our blood, that we might have kept out.
Did you ever think why, after you have been running hard for a long
time, your legs ache? Or why they stop aching when you sit down to
rest, but don’t stop at once? It is these same fatigue toxins. You
explode your muscle cells faster than the blood can wash away the
products of the explosions. So these accumulate. By and by, they
begin to poison the muscle, and you begin to feel the pain. If you
keep on working, as people have to sometimes in spite of weariness,
the ache and the poisoning gets worse and worse, till the muscle
simply refuses to work any longer.
If you stop to rest, the ache of weariness still continues. But
after a little, the blood stream washes the muscle clean. Then the
ache is gone, and you can get up and run again. Nevertheless, a
whole day’s play or work will so load up the blood with toxins that
it can no longer wash the muscle clean. Then you must take a longer
rest, go to sleep, and give time for the blood itself to clean up.
Perhaps you have noticed (if you haven’t, try it—only don’t lie on
the damp ground) that when your legs are tired, they rest and stop
aching much more quickly if you put your feet up higher than your
head. This is, of course, because the blood current coming from the
tired muscles, can run down hill, and so most easily drain off the
toxins which make the ache. So too, you can keep fresh much longer,
whether you are working or playing with the muscles, or sitting
still and working your brains over your lessons, if you stand up
properly and don’t slouch. When you slouch, you cramp your lungs.
The cramped lungs fail to clear the blood. The dirty blood fails to
wash brain or muscles clean, and you get tired sooner than you
ought. For the same reason, you tire more quickly in bad air. But if
you give blood and lungs a fair chance, they will do a lot of
resting for you while you are still at work.
But long before we get in the least tired, we get out of breath.
Poisons as before, only this time it is largely the carbon dioxid
that does the business. The muscle-sugar explodes, and forms the
carbon dioxid. The carbon dioxid leaks out into the blood; and the
blood, circulating thru the body, carries it to a certain nerve
center high up in the back of the neck. This in a sense tastes the
carbon dioxid, something as the tongue tastes it in a glass of soda
water.
When the nerve center in the neck tastes a little carbon dioxid, it
doesn’t say anything. But the moment the taste begins to get strong
(which is in less than a quarter minute after one starts running
hard) it telephones over the nerves to the lungs: “Here, here, here!
What is the matter with you fellows. Get busy. Breathe hard. This
blood is fairly sizzling with burnt up sugar!”
Thereupon the lungs get down to work. They breathe as hard and as
deep as they can; while the heart, which has also been telephoned of
the situation, beats harder and harder, to give the lungs all the
blood they can clean, and the working muscles all the blood they can
dirty.
If heart and lungs hold their own, nothing in particular happens.
But if we keep running on too hard, so that muscles poison the blood
faster than the lungs can un-poison it, then the nerve center which
is in the back of the neck interferes once more. When it cannot make
heart and lungs work faster, it calls off the muscle. Suddenly it
gives us such a feeling of loss of breath and suffocation, that we
simply cannot run another step. We have to stop. Then heart and
lungs catch up on their work.
Curiously enough, getting one’s “second wind” as we say, when the
lungs after pumping violently, settle down to working steadily once
more tho we still keep on running, and “getting in training” so that
we can do all sorts of exercises without getting winded, both these
highly desirable conditions depend in part on teaching this
“respiratory center” in the neck not to raise so much of a row when
it smells a little carbon dioxid in the blood. We train our muscles
to do their work; and we also train this nerve center not to get
rattled and turn on that feeling of suffocation until it absolutely
has to. We get it used to burnt muscle-sugar so that it doesn’t mind
the taste as it did.
So, as I say, we live only by just escaping being mildly poisoned.
But the curious thing about it is that among these various poisons
which would certainly kill us forthwith, if we did not promptly get
them out of our bodies, stands, of all things, sugar.
We eat a good deal of sugar in our food. We make a good deal more
out of other sorts of food. If we did not make sugar, and have it
always on hand in our blood, we could neither work nor live. And yet
thousands of persons, every year, die of nothing in the world but
sugar poisoning.
Sugar is so very poisonous that we have a special arrangement in our
livers for keeping down the amount that at any one time gets into
the blood. But for this, a box of candy, or a meal of bread and
potatoes would inevitably kill us within three hours. The blood of a
full grown man always contains about a quarter ounce of sugar, that
is to say, two ordinary lumps. If he has less than two lumps, he
begins to starve. If he has more than three or four lumps, his head
feels heavy and he cannot keep awake. He begins, in short, to be
poisoned. But any one who should get his blood half as sweet as he
takes a cup of tea or coffee, would promptly drop into a sleep from
which he would never wake up at all.
One thing then that the liver is for is to catch the sugar as it
goes by, after a meal, and store it up where it will do no harm.
Then it slowly feeds it out again, as the muscles use it up, always
keeping the amount in the blood at two lumps. But if we eat or make
more sugar than the liver can pack away, then the rest is changed
into fat and stowed under the skin and around the muscles. So we
store our food as fat, and use it as sugar—fat, luckily, being one
of the few things we make in our bodies that are not poisons.
XXXIX
Snake Venoms and Others
The life of any creature, man, animal or plant, is one long fight
against being poisoned. The poisons get us in all sorts of ways.
Some, like strong acids and caustics, actually destroy the flesh,
just as they would eat a hole thru the top of a stove, and we are
crippled or die for lack of a lining to our stomachs. A great many
poisons, like alcohol, ether, chloroform, the various alkaloids,
such as strychnin and atropin and cocain, which we use as medicines,
and nicotin, which is the alkaloid of tobacco, the poisons of many
toadstools, caffein (don’t call it caf-een, but caf-fe-in, like
co-ca-in) which we get in tea and coffee (and therefore ought not to
drink either till we are quite grown up) and half a thousand others,
mostly with names ending with “in” and the ptomains (again it’s
three syllables, to-ma-in) which form in fish and ice-cream that
have been kept too long, and poison whole families at once, all
these do not do any special harm in the stomach. But when they get
into the blood stream, they go straight for the nerves and upset
them. Ether, chloroform, and cocain, as we all know, begin by
paralysing the pain nerves. The pain sense is cut off from the
brain, so that no matter how much damage is being done, we don’t
know anything about it. And a mighty good thing it often is that we
don’t!
Other poisons attack the blood. The fumes from burning charcoal and
some sorts of gas that we use for lighting and cooking, lock the
oxygen of the air so tightly to the red blood corpuscles that are
carrying it to the cells, that the cells cannot get it away from
them. So the tissues die from lack of air, tho there is plenty and
to spare in the lungs and the blood—only the blood hangs onto it,
and the rest of the body cannot pry it loose. Snake poisons, also,
kill by attacking the blood, thus cutting off the supply of air.
These dissolve the blood corpuscles that carry the oxygen, and
literally “turn the blood to water.” Then the blood, having no
corpuscles, cannot carry oxygen to the cells of the body, and the
body dies of suffocation, tho the lungs take as much air as before.
Snake venom, therefore, does not do the least harm in the mouth or
stomach. One can suck the poison from the wound made by the snake’s
teeth, and spit out the poisoned blood, or even swallow some of it,
without the least danger. One could wash himself in rattlesnake
poison, and take no harm, so long as he kept a whole skin so that
nothing got into his blood.
Perhaps you know that pigs are the great enemies of rattlesnakes,
killing them and eating them up as if the serpents were so many
apple parings. The rattlesnakes bite the pigs. But the pig’s skin is
thick, and under it is a great layer of fat, in which there is
almost no blood. So when the pig gets a dose of poison under his
skin, enough to kill two or three men, he does not mind it at all.
The venom, shut up in the fat, works out into the blood so slowly
that the pig can make new blood corpuscles almost as fast as the
poison destroys the old ones. So at the worst, the pig feels only a
little discomfort. But the rattlesnake is safely tucked away in the
pig’s inside, where it will never do any more biting.
What I want you to remember, then, is this: All living things are
poisonous. We, ourselves, are continually manufacturing in our
bodies carbon dioxid, sugar, ammonia, and a score of other things,
any of which would soon put an end to us if we did not have a
special machinery for getting rid of them before they get a chance.
A great many plants produce also certain special poisons, strychnin,
nicotin, and the like, which would kill them if they made too much.
A few animals, too, like the snakes and some fishes and various
insects, manufacture poisons, which also would kill them. In
general, the blood of any animal is a poison to an animal of any
other sort, and always a poison of the same sort as snake venom
which does no harm in the stomach, but is fatal when enough is taken
into the blood. In general, then, each creature has some means of
getting rid of its own poisons, but the poisons of any different
sort of creature will kill it.
XL
Of Measles and Rusty Nails
Little boys sometimes get careless on Fourth of July. Perhaps they
let a cracker go off in their fingers. Perhaps they pull off a toy
pistol without noticing where it is aimed. Boys have been known to
do both these things.
When this happens someone is pretty likely to get a hole blown in
his skin. That of itself is not especially serious; the hole will
soon close again. But we are pretty certain to be dirty on the
Glorious Fourth, especially if we have been round the streets, in
the dust that people’s feet are stirring up. So when we blow holes
in our skin, we are pretty likely to blow dirt in also.
City dirt has a great many different things in it. Among them,
almost always, certain very small plants, far too small to be seen
except with a pretty strong microscope. These are, in fact, a
particular kind of bacteria. So we blow thru our skins, hole, dust,
and bacteria. The hole heals over, but the bacteria stay inside.
Being living plants, they grow in the blood—like mold in bread or
yeast in dough. Being living things, as they live, they make
poisons. It happens that this particular plant makes an especially
deadly poison, which goes straight for the nerves. Then the victim
has convulsions, and almost always dies within a few days.
This is, in fact, the dreaded tetanus or “lockjaw,” which used to
kill scores of boys and girls every Fourth of July. Sometimes, too,
one catches it by stepping on a rusty nail, not because the rust on
the nail does any special harm, but because a rusty nail is likely
to be a dirty nail also, with the tiny living plants mixed in the
dirt. We rarely get lockjaw from an ordinary cut with a sharp knife,
because such a wound bleeds freely and washes itself out. The
dangerous wounds are small deep holes and ragged tears, that give
the little living plants a chance to hide and grow.
All catching diseases are like Fourth of July lockjaw. Measles,
whooping cough, chicken pox, ordinary colds, grip, and many most
dreadful sicknesses of which people die, all such are caused by some
living thing which gets into our bodies, grows there, and living and
growing, poisons us with its waste products. Some of these plants
grow in the lungs, like that which causes consumption. In some, like
diphtheria, the growth is in the throat. In summer complaint, which
sickens the babies in the hot weather, the trouble is in the bowels.
Even some sorts of baldness are due to growing things at the roots
of the hair. Mostly, however, the plants grow in the blood. In any
case, the poisons they make get into the blood; and there they
poison the nerves, like the various alkaloids I told you about, or
else they attack the blood itself, as the snake venoms do.
[Illustration: The minute animal which causes the “sleeping sickness.”]
Some of these disease-making things, too, are not plants but
animals. Such, for example, is the minute creature that causes
malaria; and another that makes the dreadful “sleeping sickness”
that every year is killing thousands of wretched negroes in Africa,
in spite of all that can be done to prevent it.