Now, then, we have got hold of the secret of respiration; the _oxygen_
within us unites itself to the _hydrogen_ and _carbon._
And for what purpose, do you suppose?
Unquestionably it must be to make a fire, since they never come together
without doing so.
But what do people make fires for? I ask next. Well! surely to warm
themselves, do they not?
And this is the history of your body being warm exactly like a
dining-room stove, where the oxygen in the air forms an alliance with
the hydrogen and carbon of the wood. Nature warms little girls inside,
on precisely the same plan by which men warm their houses in winter.
Imagine, then, a little stove, furnished with little arms for helping
itself out of the wood-basket as it is wanted, and with little legs
to run and refill it when it is empty; the fire must be always burning
there, and the stove must be always warm.
Just such a little stove is your body; your mouth being the little
door, by which there constantly enter--not wood, that would hardly be
pleasant--but--hydrogen and carbon under the forms of bread, mutton
broth, cakes, sweetmeats, and all the good things people have learnt
to make with sugar, fat, and flour. There is hydrogen and carbon in
everything we eat, as I have already told you; but sugar, fat, flour,
and _wine_ are the substances which contain them in the greatest
quantities, and consequently they are our best _combustibles._
You are surprised, perhaps, at _wine_ being a combustible; wine,
which you think would put out rather than make a fire.
And it would. But that is only because in it, what is good for burning
is mixed with a great deal of water, which prevents our being able to
set it on fire. But if part of this water is withdrawn, you have
_brandy,_ which lights easily enough; and if part of the remaining
water is withdrawn from the brandy, you have _spirits of wine_, which
takes fire more easily still. If you have ever seen a _spirit-of-wine_
lamp, you must know something about this. Judge from that what a fire
spirits of wine must make in the body, even when it has a good deal of
water with it; for it is right to tell you that your little stove is
very superior to the one in the dining-room, and that it hunts out for
consumption the smallest portions of combustible matter, in places where
the other would be a good deal puzzled to find them.
This is not all, however. I have much greater wonders to tell you yet.
What should you say to a stove, which, summer or winter, night or day,
in rain or sunshine, amid the ice of the pole, or under the sun of the
equator, was able to keep itself constantly in the same condition;
neither hotter nor colder one minute than another, whether you gave
it much or little fuel, at a given moment, and sometimes when you gave
it nothing for whole days together? It would be worthy of a fairy tale,
would it not? Yet the human body is a stove of this description.
But this requires a little explanation.
It is rather bold in me, you may think, to assert so freely, that all
the year round, from one end of the earth to the other, the human body
is never colder nor hotter than mine is, for instance, at this present
moment. "Hot" and "cold" is soon said, you argue: but the exact
varieties of _more_ or _less_ are not so easy to measure, and especially
not easy to remember, with reference to so many bodies, scattered over
the face of the whole earth. What may be warmth for one in one case, may
not be equal warmth for another; and even supposing that the same
individual learned man could go and inspect every part of the globe in
succession, how could he possibly recall, while touching the body of a
negro in Senegal, in July, the exact amount of animal heat he had found
in a Greenland Esquimaux in January?
Be content. I should not have settled the question so cavalierly, if
people had not discovered an infallible method of estimating accurately,
and always in the same manner, the degree of warmth, in other words,
the _temperature_ of the body.
Let us first see, then, what this method is, though it will oblige us
to digress a little; but you are accustomed to that now, surely; and
besides, if I were to go straight ahead, you would not be able to
follow me.
Do you ever recollect being very cold? Let mammas look after their
little girls as much as they please, to prevent it, it is sure to
happen to every one some day or other. Now does it not seem at those
times as if the whole body were contracting itself--and when people
are shivering with cold, have they not a shrunk, shrivelled look? When
the weather is very hot, on the contrary, our bodies feel as if they
were swelling and stretching, and one seems to take up more room than
before. This is the case with all bodies. Heat swells, or, as learned
people call it, expands, them: cold shrinks or contracts them.
Furthermore, _mercury_ is one of the things most susceptible of this
action of heat and cold, and we have had recourse to it accordingly, in
the construction of the _thermometer_, [Footnote: _Thermometer_ comes
from two Greek words: _thermos_, heat; and _metron_, measure. The
degrees in the Thermometer about to be described are marked on the
_Centigrade_ principle. [Not the one (Fahrenheit) in general use in the
United States.]] a very useful instrument, which you will hear spoken of
all your life.
The _thermometer_, or _heat-measure_, consists of a little hollow ball
filled with mercury, out of which rises a small tube of very thin glass,
in which the mercury can move up and down. When the thermometer is
exposed to heat, the heat causes the mercury to expand, so it goes up
the tube; when the thermometer is exposed to cold, the mercury contracts
and sinks again.
Now suppose you were to melt some ice in the palm of one hand, and try
to dip a finger-tip of the other in a saucepan of boiling water; you
would find a great difference of temperature between the two, would
you not? Which difference of temperature people have succeeded in
measuring with the thermometer, as accurately as your mamma measures
a piece of cloth with her yard measure.
This is how it is done:
You surround the ball of mercury with pounded ice, and while it is
melting make a mark at that point in the tube where the mercury has
stopped in its descent. Then plunge the thermometer into boiling water.
Whereupon the mercury goes up, up, up, till at last it reaches a point
beyond which it will not pass. Here a second mark is made, and the
space between the two marks is divided into a hundred perfectly equal
parts, indicated by so many small lines, which are called _degrees_. But
this word _degrees_ has a double meaning in some languages. It means
_steps_ as well as the degrees of measurement we are talking about;
steps being, as you know, the perfectly equal parts into which a
staircase is divided. Fancy the mercury-tube a staircase, then, rising
from the cellar where the melting ice is, up to the garret where the
boiling water is, and let it consist of 100 steps. The mercury goes up
and down this staircase, according as the temperature it encounters
approaches that of the boiling water or of the melting ice; and if you
wish to know exactly how far it is from the cellar or from the garret,
you have only to count the _steps_. Hence arise those expressions which
you so often hear--high temperature and low temperature. These mean,
temperature according to which the mercury goes up or down this
staircase.
On the actual floor of the cellar where the ice melts, there are yet
no degrees (a floor is not a _step_, you know), so there you find the
word _zero_, which means a cipher or nought. Then you begin to count 1,
2, 3, 4 degrees, marked by lines up to 100, where you reach the garret,
_i.e._ the boiling-water height.
Of course, if the thermometer be exposed to an amount of cold greater
than that of melting ice, the mercury will sink below the cellar.
Accordingly the staircase is carried below it, with steps (so to speak)
of precisely the same size as those above, and you count as before,
1, 2, 3, &c., as it descends; adding however, to distinguish these
degrees from the others, "_below zero_." You may go on in that
way as far as 40; but there you must stop. At that point the mercury
freezes. He sits down there on his last step, and will not go any
further!
In the same way if the thermometer is exposed to a heat greater than
that of boiling water, the mercury will rise higher than the garret.
So the staircase is made to go up higher, and always with steps of the
same size, counting from 101 upwards, as far as 350 if you choose; but
no further, observe! If the temperature were raised beyond that, the
mercury would begin to boil, and then, indeed, good-bye to steps and
measured degrees! The gentleman would dance so fast that there would
be no possibility of seeing anything, to say nothing of his flying
away!
Now nothing is easier than to use the thermometer. You place it in the
situation where you want to measure the heat, and the mercury goes up
or down of itself until it reaches the degree which corresponds with
the temperature of the place. It is much more convenient than your
mamma's yard measure, which has to be moved about over the stuff, and
which is very apt to slip if you do not hold it carefully. Dressmakers
would be delighted to have a measure which only wanted laying upon the
material, and which would unroll itself and stop short just at the
proper point. And this kind of office the thermometer really performs.
We will suppose to-day to be the 30th of November. I have just carried
the thermometer out of doors; the mercury has fixed itself at the
second degree _below zero_. This tells me that it is freezing
cold. My fingers have told me so already; but exactly to what extent
they could not say. Just now in the room, the mercury was at the 15th
degree _above_ zero, thanks to the stove in which we have a good
fire. In summer-time it rises to 25, 26, or 28 degrees. I once saw it
climb as high as 33 degrees: in the shade of course, you understand;
in the sun it would have been quite another affair. Well! there was
a universal outcry against the heat. Grown-up young ladies whom I try
to teach all sorts of things as I do you, pretended that it was
impossible to work. Yet I should find a still greater heat inside my
body, if I could get the thermometer there. Have no fears, however;
I am not going to make a hole in it: luckily there is one already. I
put the ball of mercury into my mouth. And now I can almost tell without
looking. The mercury was on its way up the staircase as soon as I took
the ball in my hand--and now it has reached the 37th step.
You can try the experiment on yourself, but I forewarn you that it
ought to be rather hotter with you than with me: the mercury will
probably rise a degree higher. I will not promise that in your
grandpapa's mouth it may not sink a degree--but that will be all. In
different mouths it has, between the 38th and 36th degree, room for
the play of a little variation, but it can no more go beyond these
than a tethered cow can get beyond the circle made by her cord as she
turns round the stake. Go round the world with your thermometer, pop
it into everybody's mouth, wiping it if you choose as you proceed, you
will always find the mercury on guard. Its tethering cord is somewhat
elastic, like everything else about us; but if by any accident it
should exceed its limit by even one degree above or below, it would
be quite as extraordinary as meeting a giant of eight feet, or a dwarf
of three--which one does see occasionally, although the standard of
human height varies generally round the centre of five feet.
Since there is a fire always kept burning within us, there is no
difficulty in comprehending why our bodies always keep warm. Of course,
however, the fire must be kept brighter in winter than in summer, but
people have no need to be told so. Nature provides for the necessity.
She gives us more appetite in cold than in hot weather; not that we
can perceive much difference in ourselves in this respect from winter
to summer; for our bodies stick to their accustomed habits, and call
out pretty loudly for the same daily rations, though without having
the same need of them. In order to estimate fairly the connexion which
exists between the internal need of food--_i.e.,_ of combustible
matter--and the external temperature, we must compare the Hindoo, who
lives on a pinch of rice a day, between the tropic and the equator,
with the Esquimaux, who, to keep up his 37 degrees of heat, beyond the
polar circle, in a country where European travellers have seen mercury
freeze, sometimes swallows from ten to fifteen pints of whale-oil at
a sitting! Just fancy _whale-oil!_ which is much nastier than
even cod-liver oil, if you ever tasted that; but, on the other hand,
it is a thorough _combustible_, and the poor people are not so
very particular: come what will, the fire must be kept up, and that
briskly. But without going thus into extremes, a friend of mine once
told me that in Portugal, the land of oranges, it is not uncommon to
see gentlemen and ladies (that is to say, those who can eat and drink
what they please) dine standing, in five minutes, on a bit of bread
and whatever else may be handy. Propose this system to the inhabitants
of our colder and damper climate, whose very young ladies, fair and
delicate-looking as they are, need a helping of good roast-beef for
dinner to keep life in them, and they would only laugh at you. But
those who were well instructed could go on to inform you that the
chilly atmosphere of northern countries creates the necessity for a
more active internal fire than is ever needed under the burning sun
of Portugal, and that a mouthful of bread per day will not, in their
case, suffice to maintain the appointed thirty-seven degrees of heat.
For the same reason, Spaniards drink water, and are satisfied; whereas
English wine-merchants add brandy to a good many foreign wines, or
they would be quite unacceptable from being deficient in combustible.
It is for the same reason, also, that Russians can swallow, without
wincing, bumpers of brandy which would kill a Provençal outright: and
that the Swedish Government has no end of trouble to keep the country
people from converting into brandy the corn that ought to go to the
miller; whilst the Mohammedan Arabs accept without difficulty that
precept of the Koran which forbids the use of wine and spirituous
liquors. It is easy for the Arabs, who are kept warm by their climate,
to do without brandy. It is less easy for the Swedes, who are surrounded
by cold.
All this comes as a matter of course, and we do the same thing
ourselves, without being unusually sagacious. In January, when the
thermometer goes down to twelve or fifteen degrees below zero, I put
more fuel into my stove than I am doing to-day, with only two degrees
of cold to bear with. There is nothing surprising in all this.
The wonderful thing is, that when an Englishman goes to India, he takes
his roast beef and his spirits with him, and in a temperature of more
than thirty degrees of heat, quietly heaps up fuel in his stove, just
as if he was in England, or nearly so. You think he will set fire to
the house, perhaps. But no. Send the thermometer to his mouth for
information, and it will only mark down thirty-seven degrees; neither
more nor less than in the mouth of a rice-eater! The stove has more
sense than its owner. It only burns just what hydrogen and carbon it
wants, and takes no more trouble about the remainder than if it had
not been eaten.
How about the remainder, then? you ask; if it is not consumed for use,
what becomes of it? Do you remember, my dear child, that long ago,
after explaining the office of the bile and the liver, I put off telling
you what the bile _consisted of_, until we had talked about the lungs
and respiration? Well, the time has come now; so listen.
The hydrogen and carbon which is not consumed by the oxygen in the
blood, is seized upon by the liver, who employs it in the manufacture
of bile. Therefore the greater the amount of unemployed hydrogen and
carbon there is in the blood, the greater is the quantity of bile
manufactured by the liver--that is all. When once the body has attained
to its proper degree of heat, it is in vain you load it with
combustibles; it will not get any warmer, do what you will. Only you
will have cut out so much extra work for the liver, and the poor wretch
will have to get through it as he can. Accordingly, what happens in
the long run to our great eaters and drinkers, whether in India or
elsewhere? The bile-manufacturer, overwhelmed with work, gets worn
out at last, and kicks; and people come home with that miserable
disease, which is called the "liver-complaint."
This is one explanation of that wonderful uniformity of temperature
which, happily, human imprudence cannot disturb. But the blood has a
second resource for getting rid of its superfluity of hydrogen and
carbon, and herein especially is displayed the beautiful foresight
with which everything about us has been prearranged. We are told that
wolves, when they get hold of a larger piece of meat than they care
to eat at the moment, carry off what they do not want to some corner
and bury it in the ground, whence they get it again when their hunger
returns. Dogs sometimes do the same; and the blood has a similar
instinct. Listen attentively, for this is very interesting.
I light a candle and you see a bright flame, which will last as long
as there is any tallow below the wick. Can you tell me what it proceeds
from?
Nay, do not laugh at the question; it is quite to the purpose, I assure
you.
We know, do we not, that the substances which burn best are those which
are full of hydrogen and carbon? Tallow, then, is one of those
substances. But tell me further, if you please, what is tallow?
Tallow is _mutton fat_, allow me to say, if you never heard it before.
Now comes the question, who provided the sheep's fat with such a
quantity of hydrogen and carbon as to qualify it for making candles?
The sheep's blood undoubtedly, since blood is the purveyor-general of
living bodies--of the sheep's body as well as of our own.
But how came it that the sheep's blood had so large a stock of these
materials?
Undoubtedly, again, because there was more of them in the food the
sheep had eaten than the oxygen was able to consume or the liver to
employ. In short, the sheep has lungs and a bile-manufactory, as we
have; oxygen performs the same office for it as for us. What takes
place in its body in the matter of respiration is an exact counterpart
of what happens in ours, and the history of its fat is simply the
history of our own.
Now do you think it is for our sakes that the sheep's blood deposits
its fat in little pellet-like morsels throughout the body; do you
suppose the poor creature works in this manner merely to have the honor
of providing us with candles? It is not likely. I was talking about
the wolf just now; but there is no need to look beyond ourselves. In
many poor people's cottages there is somewhere an old earthen pot in
which the savings of each day are carefully put by, penny by penny,
as a last resource in time of need. Should a wicked thief succeed in
murdering the owner and laying hold of the treasure, he will squander
in a few hours of brilliant revelry the precious hoard so slowly got
together as a provision for possible needs. And this is what man does,
when he kills the sheep and takes its fat to make candles of! The poor
animal's blood knew well that bad times might come, that grass might
fail, and the combustible matter conveyed into the body become
insufficient to maintain its thirty-nine or forty degrees of heat
(which is the sheep's measure, who is rather hotter than we are). So
it quietly laid up its surplus stock of combustible so conveniently
brought to hand, and destined to be burnt little by little in the
depths of the organs, should times of scarcity arise. But here steps
in man, the universal thief of Nature, and turns it into a beautiful
flame, regardless of cost, and burns in one evening what his victim
had been economizing for so long. To burn for burning's sake, however,
has always been the fate of tallow, the only difference being in the
way it is done. Like the poor man's clumsy pence, which were put by
to be spent some day or other, only in another manner. It is worth
noting here, that some of the Russian soldiers who were in France in
1815 had a very good idea of restoring candles to their original
destiny. As children of the north, driven to get fire wherever they
could, they ate all the candle-ends they could lay hold of, preferring
to burn the tallow, sheep's fashion, inside rather than out!
Fat is, then, the savings' bank of the blood; there it deposits its
savings, and there it can always find them again in time of need.
Witness the fat pig described by Liebig, the great German chemist,
which having been swallowed up by a landslip, was found alive at the
end of 160 days. Fat was out of the question there, of course; the
animal weighed ten stone less than before. We will take the illustrious
professor's word on trust, but were a few days subtracted from the
account the case would still be a splendid example of the resource
which blood finds in fat when other nourishment fails; for the pig had
certainly been breathing during the whole 160 days, and as, in all
probability, he moved about much slower than usual, his hydrogen and
carbon fire was never extinguished for a single instant; of that I am
perfectly certain, and you shall soon know why. It was well for the
poor fellow himself that he had put by his provisions in time of plenty.
And who suffered? Why, the pig's master, who had looked forward with
pleasure to the rashers of bacon he should cut by and by from the
stores of combustibles in his larder. For once Master Piggy ate his
own bacon himself!
You understand now, I hope, by what ingenious management that marvellous
stove, called an animal, never burns too much fuel, whatever be the
quantity it is supplied with, and how, on the other hand, it has always
as much as it wants.
I have now to explain how important it is that it _should_ always
have enough, and that this is not merely a question of heat and cold,
as with dining-room stoves, but one of life and death! Cheer up! I
have only one more word to say about Respiration, and when you have
heard it you will appreciate still better the lesson of economy which
you have learnt from Nature to-day.