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verts to their opinions, necessarily have up hill work for a time, and sometimes "break a lance with their opponents; yea, even receive a few scars in the bloodless encounter, we must console ourselves as well as we can, and "heal all their scratches with water."

PART IV.

CHAPTER IX.

AIR.

"The enjoyment of free air may be considered as a nourishment equally necessary for our existence as eating and drinking. Pure air is essentially the greatest means of strengthening and supporting life; while confined and corrupted air is a most subtle and deadly poison. DR. HUFELAND.

THERE are few circumstances essential to the preservation of health, to which so little attention is generally paid, as the breathing of pure air. A short explanation of the manner in which the atmosphere acts on the animal body, will probably be the best means of impressing on the mind of the reader the importance of a due supply of this first necessary of life. In doing this we shall be as brief as possible.

The air we breathe is a subtle and fluid substance, which surrounds every part of the globe, and which all living beings respire, either by the

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lungs, the pores of the skin,; or by both.* It is the element to which the animal and vegetable world owes its life, beauty, and preservation. All the changes which we see take place in different beings here below, depend upon air. It is so needful to the existence of animals, that the greater part of them could not live more than half a minute if they were deprived of it; and the others could not, generally, bear the want of it more than two days. It is necessary to the birds of the air, and the fish of the sea; and even plants

* Respiration, says Professor Liebig, is the falling weight, the bent spring, which keeps the clock in motion; the inspirations or expirations are the stroke of the pendulum which regulate it. In our ordinary time-pieces, we know, with mathematical accuracy, the effect produced on their rate of going, by changes in the length of the pendulum, or in the external temperature Few, however, have a clear conception of the influence of air and temperature on the health of the human body; and yet the research into the conditions necessary to keep it in the normal state is not more difficult than in the case of a clock. Dr. E. Johnson says, Respiration is as certainly performed by the skin as the lungs, and that nothing can be more certain than that nature, in her anxiety to ensure a full and perfect accomplishment of the all important func tions of respiration, has provided us with a double set of respiratory apparatus, viz., the lungs and the skin. As a proof of this, he refers to experiments, which have shown that the animal breath consists of carbonic acid, the vapour of water, and nitrogen. And that the same experiment of the same experimenters, have proved that the exhalation from the body-the breath of the skin-is also composed of the same constituents--carbonic acid, vapour of water and nitrogen-and that, therefore, perspiration and respiration, as the very words themselves would indicate, are essentially the same. Liebig also says, from the first moment that the functions of the lungs or of the skin are interrupted or disturbed, compounds, rich in carbon, appear in the urine that carbon which ought to have been given off either by the lungs or by the skin whichever of the two happen to be in fault. But important as the skin is, as our assistant organ of respiration, we utterly deprive ourselves of its assistance, by the absurd fashion of our dress, and the ridiculous care with which we defend the skin from all access of atmospheric air-thus, to a large extent, shutting out the oxygen, so vitally essential to life; and shutting in the carbonic acid, which is known to be so deadly to all animal, and also to vegetable life. When shall we learn to be wise! "When shall it once be."

in order to vegetate have need of air. Sounds could not be propagated without it, nor could winds be formed. The sun itself could not furnish us with either a sufficiency of light or heat, if the air did not surround our globe.

Every square inch of the surface of the globe is pressed by a column of air of 15lbs. weight; every square foot, by one of 2160 lbs. ; and a middlesized man, whose surface is about 14 feet carries a load of atmospheric air equal to 30,240 lbs. weight! By means of heat the air may be made to occupy a space 550,000 times greater than that which it occupies in its common atmospheric

state.

This air is a compound of different airs, called gasses; of which a gas called oxygen, (and sometimes from its being indispensable to the maintenance of animal life, vital air,) forms 21 parts in every 100; the remaining 79 parts, being a gas called nitrogen, or azote. The air which is drawn into the lungs in the act of breathing, and through the pores of the skin, acts on the blood which is returned through the veins from different parts of the body, so as to change it from dark purple to a light scarlet. In this process the oxygen disappears, having formed chemical combinations with certain substances contained in the venous blood, by which it is changed partly into a gas, called carbonic acid gas, and partly into water. A minute proportion of this gas is consequently found in the present air we meet with. The carbonic acid gas is not only unfit for the support of life, but it is positively a poison, since a given proportion of the atmospheric air will support an animal much longer, if this gas be removed as fast as it is formed, than if it be suffered to remain. By the abstraction of the substance from

which these new combinations are formed, the blood is purified and rendered fit to stimulate to proper action, the nerves and muscles; to restore the structure of the various portions of the body, which are continually becoming useless, and being removed, to furnish the secretions, as they are called, by which the process of digestion, and other processes necessary to the existence of our bodies, are performed. In short, to use the emphatic language of scripture, which has been quoted, and illustrated, by the greatest physiologists of this country-" the blood is the life thereof;" and the blood itself loses its vitality, if it be not continually purified by exposure to the action of atmospheric air.

From the above it will be evident, that if an animal be confined to a given quantity of air, every time the act of breathing is repeated, that air is contaminated, and is becoming less fit for the proper performance of the process above described. Every time the blood circulates, it consequently gets more impure, and less capable of stimulating the heart, and other organs, to action. The circulation becomes more languid, till the heart ceases to beat, and the animal dies. This truth might be proved by reference to such facts as-the short time during which a person can exist in a diving-bell—the well known story of the black-hole, or prison of Calcutta-and circumstances which have occurred, and are still occurring in the accursed African slave trade.

It is calculated that every individual consumes about five cubic feet of air in an hour, or in other words, deprives such a quantity of air of its oxygen, or vital principle. If an hundred persons, therefore, were confined in a room, thirty feet long, twenty-five broad, and thirty high, the

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