flesh cannot supply the demand, the blood does not hesi tate a moment. He boldly falls upon the most important organs, without stopping to consider; he, too, is devoted solely to his work, and that, like the baking of pots, never comes to an end by being completed; if external help does not arrive in time, the house soon be comes uninhabitable, and life slips away. The man dies of hunger.

But in the same way that poor Bernard Palissy was in reality working, all the time, for his wife and children, whose future well-being he strove for as the final end of all his efforts, though at the risk of letting them sleep under the bare heavens; so the blood was laboring up to the last moment for that very life which he at last turned out of doors; and the work of destruction which caused its final departure has had in reality the effect of prolonging its stay. Without it, all would have been over long before,

LETTER XXIV.

THE WORK OF THE ORGANS.

THUS much is settled, then. It is the blood which sets everything in motion throughout the body. The organs are idlers who would do nothing but for him; they only work when goaded on, if I may use the expression, by that fire-always on the point of going out-which he is perpetually coming back to rekindle, thanks to the oxygen he carries with him from the lungs.

This will enable me to explain many things, which, although not new to you, you have probably never tried to account for before.

To begin with: do you remember what happened to you the other day, when you tried to overtake your mischievous brother in running, and he, taking advantage of his school-boy legs, led you mercilessly through all the garden walks, without having the grace even to let you catch him at the end? You were quite out of breath; your heart beat so rapidly it almost hurt you; and you were so hot that the perspiration poured in great drops down your face, so that your mamma, quite frightened, took you up in her arms and carried you to the fire; for the coolness of evening was coming on, and a little girl drenched with perspiration is soon chilled.

Tell me now, what connection was there between your overrunning yourself in a race and the extraordinary degree of heat which came over you so soon? Your

cheeks were cool and fresh when you began to run; what made them so red all at once, and especially at a moment when the air was cool and fresh in the garden?

You open your eyes in surprise; you had never thought of this. No! that is just the way with little girls. They run; they get hot; it seems as natural as warming oneself in the sun, and they never ask why it is so.

Yet you could almost tell me the "why" yourself, if you stopped to think about it, now that you are what your school-boy brother would say "up to a thing or two;" but to save time, I will help you.

You run as a bird flies, without thinking about it. Nevertheless, if you could see with a magic glass all that takes place in your body while those active little feet are carrying it like a feather across the garden, you would be perfectly amazed. One of these days, when we have finished our present history, I will tell you that other one, which is equally worth the trouble. It is enough for the present to know, that a very complicated piece of work is being carried on there, in which almost all the muscles of the body take part at the same time, contracting and relaxing in turn, like so many springs, of which each either drives forward or holds back a part of the machine. In fact, while your eyes and thoughts are fixed on the butterfly which is flitting away from you through the air, there is going on within you such an unheard-of outlay of efforts as could never be got out of our idlers if the terrible steward did not lash them severely.

Now, his lash, as we have said often enough, is that eternal fire, the materials of which he conveys to all parts of the body. On those special occasions, therefore, he is obliged to make his fire burn much more briskly

than usual-exactly like railway engine-drivers, who increase the heat of their fire to get up steam in propor tion to the speed they wish to go.

From this you will understand that it is no great wonder that your small frame should get heated from such work as racing and chasing; and that if you pursue it too long, the perspiration which comes out all over you is sufficiently explained.

This is not all, however. The fire, whose strength has to be increased, naturally requires a larger amount of combustible matter than before, and forasmuch as there is only a certain fixed quantity in each drop of blood, whenever the muscles want more than usual, the blood itself must flow to them in greater abundance. Now if it were a question of supplying only one part of the body (as it is, you may remember, of supplying the stomach during the progress of digestion), he might contrive to accomplish his task there by neglecting it elsewhere, and overflow one organ at his case, at the expense of all the rest. But in this case he is wanted everywhere in the same abundance. It is not a question of taking one muscle's share for the benefit of another. From one end of the body to the other, all want to be deluged at once. And remember that these exigencies do not bring a drop more blood into the body. How is he to get out of his difficulty then, this overwhelmed steward of ours? Well! just as your mamma manages, my dear, when there is more to do than usual in the house-by running quicker than ever from the cellar to the garret, and from your room to your papa's! That is called doubling oneself; and this gallant blood doubles itself to some purpose. He runs and runs and runs, ar rives in hurried streams, and returns full gallop, passing and repassing through the heart, which emptics and fills

itself in sudden jerks. Unluckily, the poor heart is a delicate sort of person, who does not like having his habits disarranged, and this forced work soon makes him desper ate. The other day, in his despair, he knocked with all his strength against the walls of his little chamber, to warn his young mistress that he could bear no more, and that they were both of them in danger. In fact, you ought to know that if one was infatuated enough to go on running too long, one might die of it. When you learn ancient history, you will probably be told of what happened to the soldier of Marathon, who flew like an arrow from the field of battle to the gates of Athens, that he might tell his fellow-citizens a quarter of an hour earlier, that his country was saved; and he fell dead on his arrival.

But it is not the heart only which suffers by this mad career of the blood. During each journey it performs it passes through the lungs, which in their turn are forced to play with hasty jerks. And this is well for our good steward; for the lungs, filling with air at each descent of the diaphragm (if you remember what we have said before), more air, and consequently more oxygen, comes in, and the blood has by this means a larger stock on hand, ready to help him out in the unusual waste which is just then going on in the muscles. I spoke just now of railway steam-engines. See how selfsupporting ours is! The greater the amount of fire wanted, the faster the blood flows; and the faster the blood flows, the oftener does the coffer re-fill itself, whence comes the supply of oxygen requisite for keeping up the fire. All this goes on at once, by one impulse, and the balance between the receipts and expenditure settles it self of its own accord. How thankful many families would be if their money-chest would but fill itself in the