LETTER XXVIII.

COMPOSITION OF THE BLOOD.

ONE word more before we finish. We must not leave off without bidding a last farewell to the good servant of whom we have spoken so much; the model steward so exact in giving back everything he receives-the factotum of the house in short. We have watched him at work long enough, but I have not yet described him personally to you, nor told you exactly what he is composed of.

And here I shall be obliged to begin again with figures and calculations, although I am told young people are not very fond of them. Nevertheless, none of us can manage our affairs properly without them. Hereafter, when you are at the head of a family, you will be oblig ed to practise arithmetic, if you want to know what is going on in your house. Never allow yourself to look upon what is necessary as wearisome; the true secret of being punctual in our duties is to throw our heart and interest into them.

I choose, therefore, to suppose that you will be interested to know that 1000 ounces of blood generally contain, (for there are shades of difference between one sort of blood and another) 870 ounces of the serum I have been talking about, and 130 ounces of clot. At first sight one would take the quantity of clot to be much greater than it really is; but in the state you see

it, in the basin, it contains a considerable amount of water, which belongs by right to its companion serum, and which has to be drained away from it before it can be weighed.

Now, in our 870 ounces of serum, we shall find, to begin with, 790 of water; do not be astonished at the quantity. Most of the weight of all animals is produced by water; they weigh comparatively nothing after being thoroughly dried in a stove-when they are dead of course for neither animal nor plant can live unless saturated with water. This, by the way, may serve to explain the ease with which we can keep ourselves floating in water; we are not much more than water ourselves! Were it not for those abominable bones which are a little bit heavier than the rest, we should never sink unless a stone were hung round our necks.

I repeat then; 790 ounces of water in 870 of serum, which leaves 80. Of this, albumen furnishes seventy, and the ten others, with the exception of a small portion of fat which floats here and there ready-made, are salts. It would take too long to explain what salts are here, but there is one sort of salt you know perfectly well; viz., that which is put on the dinner-table in a salt-cellar. And it is the most important of all. More than half the ten ounces of salts consist of it alone, which will make you understand better than before, what I explained with reference to the stomach; that is, why we put salt in our food. The porter above is quite up to his business when he asks everyone who enters to produce his little bit of salt. It is an attention which the blood appreciates very highly, although table-salt is of no great use to him in his building operations; but it evidently keeps him in good humor, and he would work. badly without it. It is the same with all the animals

inan makes use of, and even the plants he cultivates, find that salt gives them an appetite. And it would almost seem as if nature had purposely dealt with us in this matter on a magnificent scale. She has made salt-magazines of the sea and the bosom of the earth, where it cxists in prodigious masses which cost nothing but the labor of stooping to pick up, except in countries where a gentleman called a tax-gatherer, stands by to count the lumps and allow them to pass on by paying a duty. For my part, if I were the government-this is a secret. between you and me, mind-I would look out for some thing else to stand in the place of the salt-tax. It is not well to interpose between man and the gratuities of Dame Nature, and to make him pay more heavily for the blood's chosen friend than she meant him to be charged.

But to proceed, the kitchen-salt being deducted from the ten ounces of salts-in-general, there remain altogether from four to five ounces, which contain. But here I stop, for it puzzles me very much how to go on! Enough, that to enable you to follow me, you would require at least as much knowledge of chemistry as will be expected of a young man who has to pass an examination in medicine. Fancy the contents of a whole druggist's shop! I will tell you a few names, that you may have a specimen of the style in use, but I forewarn you that they are not inviting: hydrochlorate of ammonia; hydrochlorate of potash; carbonate of lime; sulphate of potash; phosphate of lime; phosphate of magnesia ; lactate of soda. I spare you the others, for many others there are, without counting those which have not yet been discovered! All these things are to be found, I must tell you, in fibrine and albumen, but in such minute quantities that it is scarcely possible to recognize them

In the serum, for instance, the gentlemen are so very small, and so completely entangled one with the other, that it is startling to think of the skill and patience requisite for making them all out, to say nothing of affixing the right name-uncouth as it may seem-tc each grain of this almost imperceptible dust! He who first called man an epitome of creation, scarcely knew how truly he was speaking, for man bears about in his veins, ascertained samples of at least half the primitive substances from which all others are made, and if the whole of them should some day be found to be there, I for one should not be surprised.

This is well worth knowing, is it not? and I have not come to the end of my story yet.

We have still the 130 ounces of clot to speak about. But their contents are easily reckoned. Three ounces of fibrine and 127 of globules.

Here, however, we enter upon such a world of wonders, that I am quite delighted to be able to finish with it. It will be the masterpiece of our exhibition!

You feel quite sure blood is red, do you not? Well! it is no more red than the water of a stream would be, if you were to fill it with little red fishes. Suppose the fishes to be very very small, as small as a grain of sand; and closely crowded together through the whole depth of the stream: the water would look quite red, would it not? And this is the way in which blood looks red: only observe one thing; a grain of sand is a mountain in comparison with the little red fishes in the blood. If I were to tell you they measured about the 3,200th part of an inch in diameter, you would not be much the wiser, so I prefer saying (by way of giving you a more striking idea of their minuteness) that there would be about a million in such a drop of blood as would hang on the

point of a needle. I say so on the authority of a scien tific Frenchman-M. Bouillet. Not that he ever counted them, as you may suppose, any more than I have done; but this is as near an approach as can be made by calcu lation to the size of those fabulous blood-fishes, which are the 3,200th part of an inch in diameter.

These littles fishes are called globules; but they are not exactly shaped like little globes, as the word would lead you to suppose. They are more like little plates slightly hollowed out on both sides. The central nucleus is surrounded by a flattened margin rather bladdery in appearance, of a beautiful red color, formed of a sort of very soft and very elastic jelly. I scarcely need tell you that all this was discovered through the microscope, and moreover, by examining the blood of frogs, in which the globules are much larger than in ours.*

It was in 1661-rather more than two hundred years ago that an Italian and a Dutchman discovered, each by himself in his own country, the microscopic popula tion of the blood. The name of the Italian is not very difficult-Malpighi. As to the Dutchman's, you must pronounce it in the best way you can-he was called Leeuwenhoek. You smile, but he was nevertheless one of the first men who really comprehended what a wonderful auxiliary human science had just got hold of in the microscope, and he has helped to open the eyes of the world to the marvels of miniature creation. So col.

* Authentic portraits of these globules drawn-so to speak-by Nature herself, are to be seen on the admirable Photographs obtained by Bertsch, with the aid of the solar microscope, invented by himself and Arnaud. There you see them magnified 250,000 times, and may study them at your ease, and verify my description for yourself without any fear of being deceived. You must persuade your father to procure one. This result of photography is among

the wonders of modern science.