There is a favorite conjuring trick, which always amuses people, though
it deceives no one. The conjuror shows you an egg, holds it up to the
light that you may see it is quite fresh, then breaks it;
and--crack--out comes a poor little wet bird, who flies away as well
as he can.
This trick is repeated in earnest by nature every day, under our very
eyes, without our paying any attention to it. She brings a chicken out
of the egg, which we place under the hen for twenty-two days, instead
of eating it in the shell as we might have done, and we view it as a
matter of course. Yet we do not say here that the bird may not have
come down the conjuror's sleeve, or the hen may not have brought it
from under her wing. It was really in the egg, and its own beak tapped
against the shell from within and cracked it.
How has this come about? No one can have put that beak, those feathers,
those feet, the whole little body, in short, into the egg while the
hen was sitting upon it, that is certain. It is equally certain, then,
that the liquid inside the egg must have contained materials for all
those things beforehand; and if Nature could manufacture the bones,
muscles, eyes, etc., of the chicken, out of that liquid while in the
egg, she would probably have found no more difficulty in manufacturing
your bones, muscles, eyes, etc., from it had you swallowed the egg
yourself.
Here, then, is an undeniable _aliment of nutrition_.
It is called _albumen_, which is the Latin word for _white of egg_. It
is easily recognized by a very obvious characteristic. When exposed to a
temperature varying from sixty to seventy-five degrees of heat,
according to the quantity of water with which it is mixed, _albumen_
hardens, and changes from a colorless transparent liquid, into that
opaque white substance, which everybody who has eaten "hard-boiled eggs"
is perfectly well acquainted with.
I will only add one trifling detail. 100 ounces of albumen contain as
follows:
Ounces.
Carbon 63
Hydrogen --
You can fill up this number yourself, can you not? And knowing the 7
of hydrogen, you may guess what follows! After what we have talked of
last time, here is already an explanation of the chicken's growth. But
let us go on.
You recollect that yellowish liquid I spoke about, which lies underneath
the _clot_, or _coagulum_ of the blood? I will tell you its name, that
we may get on more easily afterward. It is called the _serum_, a Latin
word, which, for once, people have not taken the trouble of translating,
and which also means _whey_. Put this _serum_ on the fire, and in
scarcely longer time than it takes to boil an egg hard, it will be full
of an opaque white substance, which is the very _albumen_ we are
speaking of. Our blood, then, contains _white of egg_; it contains in
fact--if you care to know it--sixty-five times more white of egg than
fibrine, for in 1,000 ounces of blood, you will find 195 of _albumen_,
and only three of _fibrine_; of _casein_, none.
Nevertheless we eat cheese from time to time. And we generally eat
more meat than eggs, and meat is principally composed of fibrine! I
should be a good deal puzzled to make you understand this, if we had
not our grand list to refer to.
Ounces.
Carbon 63
Hydrogen 7, etc.
_Fibrine_, casein_, _albumen_, they are all the same thing in the main.
It is one substance assuming different appearances, according to the
occasion; like actors who play several parts in a piece, and go behind
the scenes from time to time to change their dresses. The usual
appearance of the aliment of nutrition in the blood is _albumen_; and in
the stomach, which is the dressing-room of our actors, _fibrine_ and
_casein_ disguise themselves ingeniously as _albumen_; trusting to
_albumen_ to come forward afterwards as _fibrine_ or _casein_, when
there is either a muscle to be formed, or milk to be produced.
Know, moreover, that _albumen_ very often comes to us ready dressed, and
it is not only from eggs we get it. As we have already found the
_fibrine_ of the muscle and the _casein_ of milk in vegetables, so we
shall also find there, and that without looking far, the albumen of the
egg. It exists in grass, in salad, and in all the soft parts of
vegetables. The juice of root-vegetables in particular contains
remarkable quantities of it. Boil, for instance, the juice of a turnip,
after straining it quite clear, and you will see a white, opaque
substance produced, exactly like that which you would observe under
similar circumstances in the _serum_ of the blood; real _white of egg_,
that is to say--to call it by the name you are most familiar with--with
all its due proportions of carbon, hydrogen, oxygen, and nitrogen.
I wonder whether you feel as I do, dear child; for I own that I turn
giddy almost when I look too long into these depths of the mysteries
of nature. Here, for instance, is the substance which is found
everywhere, and everywhere the same--in the grass as in the egg, in
your blood as in turnip-juice! And with this one sole substance which
it has pleased the great Creator to throw broadcast into everything
you eat, He has fashioned all the thousand portions of your frame,
diverse and delicate as they are; never once undoing it, so to speak,
to re-arrange differently the elements of which it is composed. From
time to time it receives some slight impulse which alters its appearance
but not its nature, and that is all. As the chemist found it in the
bit of salad, so he will find it again in the tip of your nose, if you
will trust him with that for examination. We are proud of our personal
appearance sometimes, and smile at ourselves in the looking-glass; we
think the body a very precious thing; but yet when we look deeply into
it we find it merely so much charcoal, water and air.
This reminds me that we have not yet made acquaintance with the new
personage who was lately introduced upon the scene. _Nitrogen_ or
_azote_, I mean. He plays too important a part to be allowed to remain
in obscurity.
You have already learnt that oxygen united with hydrogen produces
water. Combined with nitrogen it produces air; but in that case there
is no union of the two. They are merely neighbors, occupying between
them the whole space extending from the earth's surface to forty or
fifty miles above our heads; together everywhere, but everywhere as
entire strangers to each other as two Englishmen who have never been
introduced! I should be a good deal puzzled to say what nitrogen does
in the air: he is there as an inert body, and leaves all the business
to the oxygen. When we breathe, for instance, the nitrogen enters our
lungs together with its inseparable companion, but it goes out as it
went in, without leaving a trace of its passage. Nevertheless, as
sometimes happens among men, the one who does nothing takes up the
most room. Nitrogen alone occupies four-fifths of the atmosphere, where
it is of no other use than to moderate the ardent activity of king
oxygen, who would consume everything were he alone. I can compare it
to nothing better than to the water you mix with wine, which would be
too fiery for your inside if you drank it by itself. This is what
nitrogen does. It puts the drag on the car of combustion; as in society,
the large proportion of quiet people put the drag on the car of progress
(let us for once indulge ourselves in talking like the newspapers!);
and such people are of definite use, however irritating their
interference may appear in some cases. The world would go on too rapidly
if there were nothing but oxygen among men. We have quite enough in
having a fifth of it!
But what in the world am I talking about? Let us get back to nitrogen
as fast as we can!
We must not imagine there is no energy in this quiet moderator of
oxygen. Like those calm people who become terrible when once roused,
our nitrogen becomes extremely violent in his actions when he is excited
by another substance, and is bent on forming alliances. Sometimes the
usually cold neighbor unites itself to oxygen in the closest bonds;
in which case the two together form that powerful liquid, _aqua-fortis_,
of which you may have heard, and which corrodes copper, burns the skin,
and devours indiscriminately almost everything it comes in contact with.
Combined with hydrogen, nitrogen forms _ammonia_, which is still often
called by its old name _volatile alkali_; one of the most powerful
bodies in existence, and one for which you would very soon learn to
entertain a proper respect, if somebody were to uncork a bottle of it
under your nose. Finally, nitrogen and carbon combined, produce a quite
foreign substance (_cyanogen_), resembling neither father nor mother in
its actions and powers, to the confusion of all preconceived ideas, when
Gay-Lussac, a Frenchman, introduced it to the world, where it fell like
a bombshell upon the theory of chemical combinations. This impertinent
fellow, combining with hydrogen in his turn, produces _prussic acid_,
the most frightful of poisons; one drop of which placed on the tongue of
a horse strikes it dead as if by lightning.
You perceive that you must not trust our worthy friend too far. You
have learnt, however, elsewhere, that it is not equally formidable in
all its combinations. Those very substances which, when paired off
into small separate groups, destroy all before them, constitute, all
four together, that precious aliment of nutrition of which we are
formed. Moreover, its real name is "_azotized aliment_" because
it is the presence of nitrogen or azote in it, which, above all,
determines its quality, so that people are in the habit of estimating
the nourishing power of our food by the amount of nitrogen it contains.
In fact, nitrogen seems to be a substance especially inclined towards
everything that has life. His three comrades wander in mighty streams,
so to speak, through every part of creation; but he, except in the
vast domain of the atmosphere, where he reigns in such majestic repose,
is rarely met with, except in animals, or in such portions of plants
as are destined for the support of animal life.
On this point I will tell you the history of his original name,
_azote_, which you will find curious enough. A short time before
the French Revolution, in 1789, the principal properties of this gas
were made known to the world by a learned Frenchman, who may be almost
considered the father of modern chemistry, and whose name I must beg
you to recollect. [Footnote: Dr. Daniel Rutherford (Edinburgh)
discovered the existence of _Nitrogen_, A. D. 1772; but he never
investigated its character.] He was called _Lavoisier_. While
endeavoring to account satisfactorily for _combustion_, which
before his time people explained any way they could, Lavoisier succeeded
in separating our two friends, the neighbors in the atmosphere, one
from the other, and was the first man in the world who managed to
secure in two bottles--on the one hand, the bubbling oxygen freed from
his tiresome mentor; on the other, the sober *azote, snatched away
from his giddy pupil. What he did with the bottle of oxygen matters
but little to us; but in the bottle of _azote_ he plunged, by way
of experiment, an unfortunate mouse, and subsequently a little bird,
both of whom, finding no oxygen to breathe, died one after the other.
Nothing could live in it, as you may suppose; and Lavoisier thought
it must be right to give so destructive a gas the name of _azote_,
which in Greek means "_opposed to life_." Meantime, science went
on progressing by the gleam of the lamp he had lit, and then followed
the discoveries of his successors, who forced their way into the obscure
laboratory where the elements of living bodies are prepared. And at
last it was ascertained that this _azote_, opposed to life as it
was thought to be, was actually an essential property of life; that
it accompanied it everywhere, and that without it the whole framework
of the animal machine would fall to pieces. It is still known by its
old name, which custom had sanctioned; but I imagine no learned man
can ever utter it now without a feeling of humility, and without the
thought that the future has possibly many contradictions in store for
him also. Besides, nitrogen has to pass through many fine-drawing
processes before it attains that post of honor which has been assigned
to it in the animal kingdom. The animal himself can do nothing with
it, unless it has been previously absorbed and digested by the
vegetable, and the vegetable in its turn could get no good from it,
were it to remain isolated and indifferent in the bosom of the
atmosphere. It is only when it has formed one of those combinations
I have been telling you about, and more particularly the second, which
produces _ammonia_, that it fairly enters upon the round of life.
And then, in the mysterious depths of vegetable existence is organized
that wonderful _quadrille_ of the _aliments of nutrition_, the history
of which has now been sufficiently explained to you.
The vegetable kingdom, therefore, is simply the great kitchen in which
the dinner of the animal kingdom is being constantly made ready; and
when we eat beef, it is, in fact, the grass which the ox has eaten,
which nourishes us. The animal is only a medium which transmits intact
to us the _albumen_ extracted in his own stomach from the juices
furnished to him in the fields. He is the waiter of the eating-house;
the dishes which he brings us have been given him already cooked in
the kitchen. But to appreciate properly the service he renders us we
must remember that the dishes to be obtained from grass are very, very
small, and that it would be a great fatigue to the stomach if it could
only get at such tiny scraps at a time; as, alas! has sometimes happened
to the famine-stricken poor, who have tried in vain to support life
from the grass in the field. But these minute dishes are brought to
us in the mass whenever we eat beef, and our stomachs benefit
accordingly. Do not forget this, my child; and when mamma asks you to
eat meat, obey her with a good grace; if, that is to say, you wish to
grow up to be a woman.