There are many ways, less often sought than found, for "becoming quite cold and warm again," but an experimenter, trying to contract a catarrh in that manner, would soon give it up as a futile enterprise; after two or three attempts he would find the attainment of his purpose more hopeless than before; he would find that instead of impairing, he had improved the functional vigor of his breathing-apparatus. Cold is a tonic that invigorates the respiratory organs when all other stimulants fail.

As soon as oppression of the chest, obstruction of the nasal ducts, and unusual lassitude indicate that a "cold has been taken"—in other words, that an air-poison has fastened upon the bronchi—its influence should at once be counteracted by the purest and coldest air available, and the patient should not stop to weigh the costs of a day's furlough against the danger of a chronic catarrh. In case imperative duties should interfere, the enemy must be met after dark, by devoting the first half of the night to an outdoor campaign and the second half to an encampment before a wide-open window.

There is no doubt that the proximate cause of a catarrh consists in the action of some microscopic parasite that develops its germs while the resistive power of the respiratory organs is diminished by the influence of impure air. Cold air arrests that development by direct paralysis; i.e., by lethargizing and eventually destroying the vitality of the disease-germs. Towards the end of the year a damp, sultry day—the catarrh-weather par excellence—is sometimes followed by a sudden frost, and at such times I have often found that a six-hours' inhalation of pure, cold night-air will free the obstructed air-passages so effectually that on the following morning hardly a slight huskiness of the voice remains to suggest the narrowness of the escape from a two-weeks' respiratory misery.

It would be a mistake to suppose that "colds" can be propagated only by direct transmission, or the breathing of recently vitiated air. Catarrh germs, floating in the atmosphere of an ill-ventilated bedroom, may preserve their vitality for weeks after the house has been abandoned, and the next renter should not move in till the whole building has been subjected to an air-bath, and till wide-open windows and a through-draught of several days has removed every trace of a "musty" smell.

About the comparative advantages of dry and moist ("marine") climates opinions are divided, with a preponderance of argument in favor of the former, but so much is certain that for the cure of lung-complaints a low temperature, with or without an excess of atmospheric moisture, is preferable to the perennial heat of the tropics. "I shall not attempt to explain," says Benjamin Franklin, "why damp clothes occasion colds, rather than wet ones, because I doubt the fact; I believe that neither the one nor the other contributes to this effect, and that the causes of catarrhs are totally independent of wet, and even of cold." ("Miscellaneous Works," p. 216.)

Nor can drugs compensate the lack of Nature's specific. In the language of our instincts every feeling of discomfort suggests its own remedy. If the proximity of a glowing stove begins to roast your shins, the alarmed nerves cry out—not for patent ointments, not for anti-caustic liniments and "pain-killers," but for a lower temperature Nothing else will permanently appease them. Millions of prisoners, school-children and factory-slaves, pine for lung-food as a starving man yearns for bread, and that hunger cannot be stilled with cough-pills, but only with fresh air.

Pure cold air is also a sovereign remedy for digestive disorders. The assimilative capacity of the human organism increases with the distance from the equator. An Esquimaux can digest a quantum of food that would crapulate three Hottentots and six Hindus. Camping in the open air whets the appetite even without the aid of active exercise. A bracing temperature exacts a sort of automatic exercise: It accelerates the circulation, it promotes the oxidation of the blood, and stimulates the whole respiratory process. The generation of animal caloric has to be increased to balance the depression of the external temperature. Hence the invigorating effect of mountain air and of sea-voyages. The first dose of the tonic can be applied in-doors by gymnastics in the ancient sense of the word that implies exercise in a state of nudity ("gymnos," in Greek, meaning simply "naked")—a few minutes' pause between undress and bedtime.

People who have got rid of the night-air superstition can almost defy dyspepsia by sleeping in a cross-draught, or in cold weather at least near a half-open window. Cold, fresh air is an invaluable aid to the assimilation of non-nitrogenous articles of food (fat meat, butter, etc.). Stifling bedrooms neutralize the effects of outdoor exercise. Winter is, therefore, on the whole the most propitious time for beginning a dyspepsia cure. In summer a highland sanitarium is the best place to start with; or, for coast-dwellers, a breezy sea-shore.

The efficacy of an air-bath as a cure of insomnia is suggested by the hypnotic influence of refrigeration. At least a dozen different species of our North American mammals get drowsy enough in cold weather to go to sleep about the end of November and postpone their awakening till spring. We sleep sounder in winter than at any other time of the year, and Dr. Franklin, who, like Bacon and Goethe, had the gift of anticipative intuitions, recommends air sitz-baths as an excellent substitutes for opiates. "In summer-nights, when I court sleep in vain," he says, "I often get up and sit at the open window or at the foot of my bed, stark-naked for a quarter of an hour. That simple expedient removes the difficulty (whatever its cause), and upon returning to bed I can generally rely upon getting two or three hours of most refreshing sleep."

It can, however, do no harm to combine an air-bath with a few minutes of indoor exercise. Perfect freedom of motion is, indeed, incompatible with the restraint of artificial teguments, and the effect of Dr. Franklin's prescription could generally be improved by gymnastics tending to stimulate the action of the respiratory organs. During sleep the blood is only imperfectly oxidized, and an accumulated deficiency of that sort (indicated by choking fits) is one of the most common causes of interrupted slumber.

The solaria, or sunbath-rooms of the ancients, probably served a similar purpose. Stoves and chimney fires—though not unknown—were rare in Athens, and in Rome were considered a prerogative of wealth; the great plurality, even of well-to-do citizens, survived the winter under a load of cumbersome garments, and now and then retired to a solarium to give their skins a chance for direct contact with the circulation-stimulating atmosphere.