The History of a Mouthful of Bread Part 17

But we are wandering from our subject. If I have allowed myself to make this digression, however, it is because I am not sorry to accustom your mind early to the idea of those wonderful transformations which nature accomplishes, and of which I could give you many other instances.

To return to our flour. As soon as all the starch is gone out of it, there remains in your hand a whitish, elastic substance, which is also sticky or _glutinous_, so that it makes a very good glue if you choose; and hence its name of _gluten_, which is the Latin word for glue.

When dried, this _gluten_ becomes brittle and semi-transparent.

It keeps for an unlimited time in _alcohol_, putrefies very soon in water exposed to the air, and is easily dissolved in a wash of soda or potash. Finally 100 ounces of it contain as follows:--

Ounces.

Carbon 63 Hydrogen 7 Oxygen 13 Nitrogen 17 --- 100

Observe the last material named. It is a new arrival, of which I shall soon have something to say.

But where am I leading you? you will ask, with all these uninteresting details about glue.

Wait a little and you shall hear.

You have probably never seen any one bled, which is a pity, as it happens; for if you had, you might have noticed (provided you had had the courage to look into the basin), that after a few seconds, the blood which had been taken away separated itself of its own accord into two portions; the one a yellowish transparent liquid, the other an opaque red ma.s.s floating on the top, and which is called the _coagulum_ of the blood or _clot_. This _coagulum_ owes its color to an infinity of minute red bodies of which we will speak more fully by and by, and which are retained as if in a net, in the meshes of a peculiar substance to which I am now going to call your attention.

That substance is whitish, elastic and sticky; and when dried becomes brittle and semi-transparent. It keeps for an unlimited time in alcohol, putrefies very soon in water exposed to the air, and is easily dissolved in a wash of soda or potash. Finally 100 ounces of it contain as follows:--

Ounces.

Carbon 63 Hydrogen 7 Oxygen 13 Nitrogen 17 --- 100

This substance is called _fibrine_. It goes to form the fibres of those muscles which are contained in a half formed state in the blood.

You are laughing by this time I know, and I also know the reason why.

I have told you the same story twice over. You have not forgotten my wearisome description of _gluten_, and here I am, saying exactly the same thing of _fibrine_! You conclude I am dreaming, and have made a mistake!

But no, I am wide awake, I a.s.sure you, and mean what I say. And if these details are the same in the two cases, it is for the simple reason that the two bodies are one and the same thing; _gluten_ and _fibrine_ being in reality but one substance, so that were the most skilful professor to see the two together dried, he would be puzzled to say which came from the flour, and which from the blood. I mentioned that our muscles existed in a half-formed state in the blood. Here is something further. The _fibres_ of muscles exist previously in full perfection, in the bread we eat; and when you make little round pills of the crumbs at your side, it is composed of fibres stolen from your muscles which enable the particles to stick together; and I say _stolen from your muscles_, because they are the _gluten_ which you ought to have eaten. I hope the thought of this may cure you of a foolish habit, which is sometimes far from agreeable to those who sit by you.

This, then, is the first great _aliment of nutrition_, and you may make yourself perfectly easy about the fate of those who eat bread.

If little girls should now and then have to lunch on dry bread, I do not see that they are much to be pitied. There is the starch to keep up their fire, and the gluten for their nourishment, and that is all they require. The porter above is the only one who finds fault. And in these days porters have become more difficult to please than the masters themselves.

Then as to babies who drink nothing but milk, you perhaps wish to know where they get their share of fibrine.

And I am obliged to own there is none in the milk itself; but, I daresay, you know curdled milk or _rennet_? The same separation into two portions has taken place there which occurs in the blood when drawn from the arm; underneath is a yellowish transparent liquid,--that is the _whey_; above a white curd of which cheese is made, and which contains a great part of what would have made b.u.t.ter. By carefully clearing the curd from all its b.u.t.tery particles you obtain a kind of white powder which is the essential principle of cheese, and to which the pretty name of _casein_ is given because _caseus_ is the Latin for cheese. I shall not trouble you now with details about _casein_; but there is one thing you ought to know. A hundred ounces of _casein_ contain as follows:--

Ounces.

Carbon 63 Hydrogen 7 Oxygen 13 Nitrogen 17 --- 100

Exactly like gluten and fibrine!

Now, then, you can understand that no particular credit is due to the blood for manufacturing muscles out of the cheese of the milk which a little baby sucks. He has much less trouble than the manufacturers at Colmar have in turning their starch into sugar; because in his case the new substance is not only composed of the same materials as the old one, but contains them in exactly the same proportion also.

We have a second aliment of nutrition, you see, and I must warn you that it is not found in milk only. It exists in large quant.i.ties in peas, beans, lentils, and kidney-beans, which are actually full of cheese, however strange this may seem to you. It would not surprise you so much, however, if you had been in China and had tasted those delicious little cheeses which are sold in the streets of Canton. They cannot be distinguished from our own. Only the Chinese (from whom we shall learn a great many things when we have beaten them so that they will conclude to be friends with us)--the Chinese, I say, do without milk altogether. They stew down peas into a thin pulp. They curdle this pulp just as we do milk, and in the same way they squeeze the curd well, salt it, and put it into moulds--just as we do--and out comes a cheese at last--a real cheese, composed of real _casein_!

Put it into the hands of a chemist, and ask him the component parts of a hundred grains of it, and he will tell you as follows:--

Ounces.

Carbon 63 Hydrogen 7, etc.

I stop there; for you surely know the list by this time!

Only the third aliment of nutrition remains to be considered, for there are but three; and I will tell you in confidence, what is stranger still, viz., that there is in reality but one! But we have had enough food for one day, and I do not wish to spoil your appet.i.te. We will reserve the rest for another meal.

LETTER XXVII.

ALIMENTS OF NUTRITION (_continued_).

NITROGEN OR AZOTE.

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 sh.e.l.l 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 sh.e.l.l 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 _alb.u.men_, 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 quant.i.ty of water with which it is mixed, _alb.u.men_ 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 alb.u.men 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 _alb.u.men_ 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 _alb.u.men_, 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 princ.i.p.ally 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_, _alb.u.men_, they are all the same thing in the main.

It is one substance a.s.suming 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 _alb.u.men_; and in the stomach, which is the dressing-room of our actors, _fibrine_ and _casein_ disguise themselves ingeniously as _alb.u.men_; trusting to _alb.u.men_ 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 _alb.u.men_ 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 alb.u.men of the egg. It exists in gra.s.s, in salad, and in all the soft parts of vegetables. The juice of root-vegetables in particular contains remarkable quant.i.ties 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 circ.u.mstances 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 gra.s.s 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-gla.s.s; 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 s.p.a.ce 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 pa.s.sage. 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!