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otherwise obtain; and this, it is to be observed, independently of the certainty with which the causes of epidemic and endemic diseases are thus produced, or are strengthened in their character,-and independently of the additions thus made to the sufferings and mortality of the class, and to the disease and mortality of all ranks and classes of the people.

"If we look," says Dr. Reid," to the fact, that less than half a cubic foot of air passes through the lungs of an adult in a minute, this estimate (of the air necessary for the purposes of the system-ten cubic feet per minute) may at first appear excessive; but if we remember, that, at each expiration, a quantity of air is emitted which mingles with an additional portion of air exceeding largely its own bulk, and that there are twenty such respirations per minute, while provision is also required for the air that affects the surface of the body, and for the endless variety of minor effects produced by furniture, lighting, heating, refreshments, &c., where no peculiar adaptations for these purposes have been introduced beyond those usually observed, it will be seen that the estimate is by no means immoderate. The real question is, not what the constitution can bear, but that amount which is conveniently accessible in ordinary habitations, and which is essential for the wants of the system. The power of the system in accommodating itself to peculiar circumstances, is very great. The amount of opium, wine, tobacco, ardent spirits, and other substances, which some individuals

COMBUSTION DETERIORATES THE AIR. 103

can habituate themselves to, though only at the expense of impairing their constitutions, is no less remarkable than the varieties of atmosphere, loaded with impurities, in which others can breathe, and even work for years continuously. Perhaps the most singular instance of this kind, exclusive of those met with in polar regions, and in a rude state of society, is to be seen in mines, where it is frequently common for the men to work in an atmosphere too impure to permit a common candle to burn, though an oil lamp, in consequence of its greater tenacity of combustion, may be maintained in action without difficulty. But numerous individuals faint in an atmosphere far less impure than that of some coal-mines, and even death has been considered to have ensued in some instances from vitiated air, though it was not sufficiently impure to extinguish a candle, no impurity but carbonic acid being known to have been present."

The condition of the air as to dryness and moisture, affects very much the supply required by the system. The dry air carries off readily and rapidly the necessary exhalations from the lungs and from the skin, by so much relieving the system from matters sought to be removed from it; while the oxygen of the air and the circulating fluids of the body are, by so much, more completely allowed to produce the necessary re-action.

The effect of a burning lamp or candle on the atmosphere of apartments, in consuming the oxygen and evolving carbonic acid, is sufficiently considerable

in its degree, to make it of importance that the supply of air in a room, should be such as to allow for this, in proportion to the degree of artificial illumination; and such should not be made use of in a dormitory, unless it is of ample dimensions, or fully ventilated in proportion to the number of its occupants.

The effect of a fire in an open fire-place, if the fire is of moderate size, and the room proportionably large, is favourable to ventilation, by causing a current of air through the room, from the door or the windows to the chimney. The policy of this, however, depends entirely on the due adjustment of the question, as to the size of the fire and the dimensions of the apartment; and, unless the coldness of the weather be very severe in degree, or the individual be of such delicate habit of body, that much would be risked by exposure to an unwarmed air, or unless the room be very large, and admits of the most satisfactory degree of ventilation, a bed-room without a fire should be always preferred. If free ingress of air is secured, and the size of the room or the smallness of the fire, renders the risk of the air of the apartment becoming unduly heated, so small as not to be worth considering, the effect of an open fire in any room must be, to promote the current of air through it, and to subserve the purposes of ventilation. Even if there be no fire in the grate, the long open flue must afford a valuable channel for the passage of air; and a fire-place with an open chimney, should accordingly be provided in every room of every house,

EFFECTS OF HEATED ROOMS.

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and more especially in every sleeping-room. Stoves or braziers, for the burning of charcoal or other fuel that produces no visible or irritating smoke during combustion, are too manifestly dangerous and unphilosophical, to require more than a passing word of caution. Where open fire-places can be had, as in Great Britain, and coals or wood in sufficient quantity, a stove without adequate flue or chimney should never be seen.

Rooms, and especially sleeping-rooms, should on

The effect of this in

no account be unduly heated. rarefying the air, has been mentioned; but, moreover, the system of the occupant becomes heated, and the vessels of the skin excited,—and the result is, either an excessive secretion from the surface of the body, and consequent and probably injurious exhaustion, or a hot, dry, and feverish skin,-and the farther consequence is, increased action of the organs of circulation, undue fulness of the vessels, and undue pressure on the nervous system, with the effect of rendering the sleep either lethargic and unrefreshing, or disturbed and interrupted by the general excitability of the system. Such effects of an overheated atmosphere on the bodily conditions, are sufficiently familiar. Even in the sitting-room, although for obvious reasons it is less marked in its degree, an overheated atmosphere commonly induces a perceptible sense of oppression in the breathing, succeeded by a feeling of drowsiness and torpor, which, if not relieved, is either followed by a deep and heavy sleep, or by restlessness and nervous irritability, to

be succeeded by languor and exhaustion. Such effects must be familiar to all who have ever occupied an unduly heated bed-room.

The air of the bed-room ought, then, to be kept at as low a temperature, as is consistent with the feelings and the health; and means ought always to be in operation, by which a constant and sufficient change of the air may be secured. In some cases, the open fire-place, whether with a fire in the grate or without one, may be sufficient to attain this end; and in other cases, the partial opening of a window at the top, or a circular ventilator in one of the window-panes, may be necessary.

For the purpose of securing the adequate ventilation of the bed-room, there should be as little of drapery and curtains about the bed as possible, and the tester of the bed should generally be as lofty as the room itself,-if indeed curtains and tester may not be wholly dispensed with. If the bed-room is not of adequately large dimensios to justify them, no tester ought to be allowed, and no more of either curtains or drapery than may be requisite to obviate the risk from any current of air, that is found likely to influence the occupant of the bed. There can be no doubt, that furniture of all kinds interferes in a greater or less degree with ventilation; and the fact may judiciously influence the extent to which it is admitted into bed-rooms; and it should be remembered particularly, that all woollen articles, as carpets, absorb the moisture from the expired air, or in damp weather from the atmosphere, rendering the

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