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Page:Popular Science Monthly Volume 18.djvu/826

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equilibrium of the blood-supply, and so an inflammatory condition is set up. When this exists the blood-vessels are enormously distended; consequently, an excess of blood passes through the part, the little cells which secrete the mucus being thus excited and working much more rapidly than when in health. In this way the enormous discharge of mucus, which accompanies a cold in the head, is accounted for.

Another effect of this irritation of the mucous membrane is sneezing, which is an effort of Nature to restore the equilibrium of the nervous center by another kind of reflex action. Sneezing in catarrh is a method Nature adopts to stimulate the prostrate nervous center, and thus enable it to reassert its proper control over the blood-supply to the part; indeed, it will be found that the effects of being exposed to a draught of cold air are often completely destroyed by a succession of sneezes. Of course, Nature does not always immediately succeed in these efforts; but, when she does not, the shock from which the nervous center suffers gradually passes away, and the blood-vessels again come under the control of the little nerves which regulate their caliber, and so the catarrh disappears in a few hours, or at most in a few days. It sometimes happens that the shock from the cold air acting upon the nervous center is of such severity that the consequent inflammation is intense enough to check the secretion of mucus altogether, and in consequence the mucous membrane is dry as well as inflamed, and the suffering very much intensified.

So far, we have only glanced at a cold in the head which passes away in a few hours, but this is not always the happy termination. There is a peculiar tendency which inflammation possesses of not leaving off where it commenced, but of invading the tissues in its immediate neighborhood, and more especially when the tissue is continuous with that primarily attacked, as is the case with the mucous membrane of the air-passages. A cold may commence in the head, and rapidly spread by what is technically termed continuity of tissue into the chest; and so what at the first promised to be only cold in the head may terminate in an attack of bronchitis, or even inflammation of the lungs.—Chambers's Journal.



THE sewers of Paris discharge 262,646 cubic metres of liquid matter every twenty-four hours. It is estimated that the quantity discharged will be increased before many years to 300,000 cubic metres daily. Each cubic metre of liquid contains two and a half

  1. Translated and abridged from the "Revue des Deux Mondes."