We now proceed to some Curious and Interesting Facts concerning Respiration, or the Act of Breathing.

Anatomists have, not unaptly, compared the lungs to a sponge; containing, like it, a great number of small cavities, and being also capable of considerable compression and expansion. The air cells of the lungs open into the windpipe by which they communicate with the external atmosphere the whole internal structure of the lungs is lined by a trans-parent membrane, estimated by Haller at only the thousandth part-of an inch in thickness; but whose surface, from its various convolutions, measures fifteen square feet, which is equal to the external surface of the body. On this extensive and thin membrane innumerable branches of veins and arteries are distributed, some of them finer than hairs ; and through these vessels all the blood in the system is successively propelled, by an extremely curious and beautiful mechanism, which will be described in some future article.

The capacity of the lungs varies considerably in different individuals.* On a general average, they may be said to contain about 280 cubic inches, or nearly five quarts of air. By each inspiration about forty cubic inches of air are received into the lungs, and at each expiration the same quantity is discharged. If, therefore, we calculate that twenty respirations take place in a minute, and forty cubic inches to be the amount of each inspiration, it follows, that in one minute, we inhale 800 cubic inches ; in an hour, the quantity of air inspired will be 48,000 cubic inches; and in the twenty-four hours, it will amount to 1,152,000 cubic inches. This quantity of air will almost full 78 wine hogsheads, and would weigh nearly 53 pounds. From this admirable provision of nature, by which the blood is made to pass in review, as it were, of this immense quantity of air, and over so extensive a surface, it seems obvious, that these two fluids are destined to exert some very important influence on each other; and it has been proved, by a very decisive experiment of Dr. Priestley's, that the extremely thin membrane, which is alone interposed, does not prevent the exercise of the chemical affinity which prevails between the air which is received in the lungs, and the blood which is incessantly circulating through them. It must surely, therefore, be of the first importance to health, that the fluid of which we hourly inhale, at least, three hogsheads, should not be contaminated by the suspension of noxious effluvia.

* An instrument, called the Pulmometer, has been invented, which enables us to measure the capacity of the lungs, and which may communicate information to the physician, of some importance, in diseases of this organ.

The purity of the atmosphere may be impaired either by the operation of what some denominate natural causes, or by the influence of circumstances resulting from our social condition. Its chemical constitution is changed by respiration; the vital principle is destroyed, and its place supplied by a highly poisonous gas.

The emanations from the surface of our bodies contribute, in a still greater degree, to vitiate the atmosphere, and to render it less fit for the healthful support of life. Many of the organs which compose our wonderfully complicated frame are engaged in discharging the constituent parts of our bodies, which, by the exercise of the various animal functions, are become useless, and, if retained, would become noxious. Physiologists have instituted a variety of experiments, to ascertain the amount of the exhalations from the surface of the body. Sanctorius, an eminent Italian physician, from a series of experiments performed during a period of thirty years, estimates it as greater than the aggregate of all our other discharges. From his calculations it would appear, that if we take of liquid and solid food eight pounds in the twenty-four hours, that five pounds are discharged by perspiration alone, within that period; and of this, the greater part is what has been denominated insensible perspiration, from its not being cognizable to the senses. We may estimate the discharge from the surface of the body, by sensible and insensible perspiration, as from half an ounce to four ounces per hour.

The exhalations from the lungs and the skin are, to a certain extent, offensive even in the most healthy individuals; but when proceeding from those labouring under disease they are in a state very little removed from putrefaction.

Animal miasmata, like all other poison, become more active in proportion to the quantity which we imbibe. When, therefore, the air is stagnant, and when many individuals contri bute their respective supplies of effluvia to vitiate it, the at mosphere necessarily becomes satured with the poison; and when inhaled, conveys it in a more virulent and concentrated state to the extensive and delicate surface of the lungs.

The collection of animal effluvia in confined places is the source of the generation and diffusion of febrile infection, but when the miasmata are respired, in a diluted state, the ill effects which they produce, though slower in their operation, are equally certain. They, to a certain extent, pollute the fountain of life, and ultimately break down the vigour of the most robust frame; impairing the action of the digestive organs, engendering the whole train of nervous disorders, and rendering the body more susceptible of disease.

The lungs and the skin may equally become the means of introducing poisonous or infectious matter into the constitution. The venom of a poisonous animal, the matter of smallpox, and many other contagions, produce their influence through the medium of the skin. Infectious diseases are communicated by the reception of air in our lungs, impregnated with contagious matter. The influence of the constant respiration of air in any degree impure, is fully evinced in the pallid countenances and languid frames of those who live in confined and ill-ventilated places; and the health of all classes of society suffers precisely in proportion to the susceptibility of their constitutions, and according to the greater or less impurities of the air which they habitually respire.

Of the offensive nature of animal effluvia, the senses of every one who enters a crowded assembly, must immediately convince him. When, therefore, we reflect on the state of the air which we breathe in churches, theatres, schools, and and all crowded assemblies; and when we consider the amount of the exhalations emitted by each individual, and the very offensive nature of those emitted by many; and when, on the other hand, we take into consideration the importance of air to life, and the great quantity of this fluid which we daily respire, we must be naturally led to the adoption of such measures as would secure in our private dwellings, as well as in our public buildings, a full and unintermitting supply of fresh atmospheric air.

It is curious to observe the influence of habit, in reconciling us to many practices which would otherwise be considered in the highest degree offensive. Thus, while, with a fastidious delicacy, we avoid drinking from a cup which has been already pressed to the lips of our friends, we feel no hesitation in receiving into our lungs an atmosphere contaminated by the breath and exhalations of every promiscuous assembly.

"Were once the energy of air deny'd,

The heart would cease to pour its purple tide The purple tide forget its wonted play, Nor back again pursue its curious way."