of oxygen, taken in at each breath is to a certain extent counterbalanced by an increased frequency and depth of the respirations, and a greater capacity of the chest.  In this country, alterations in the barometric pressure are chiefly valuable as indicating an approaching change in the wind, and as well as of the amount of moisture in the air; hence the instrument is often called “the weather glass.”  A sudden diminution in the atmospheric pressure is likely to be attended with an escape of ground air from the soil, and therefore to cause injury to health, especially among the occupants of basement rooms, unless the whole interior of the building be covered with concrete.

Temperature.—­Experience has shown that man can bear greater variations of temperature than any other animal, as in the Arctic regions a temperature of -70 degrees Fahrenheit, or more than 100 degrees below freezing point, can be safely borne; that he can not only live but work, and remain in good health, in these regions provided that he be supplied with suitable clothing and plenty of proper food.  On the other hand, man has existed and taken exercise in the interior of Australia when the thermometer showed a temperature of 120 degrees Fahrenheit, or nearly 90 degrees above freezing point, so that he can live and be in fairly good health within a range of nearly 200 degrees Fahrenheit.

The effects of a high temperature vary very much according to the amount of moisture in the air, as when the air is nearly saturated in hot climates, or even in summer in our own, more or less languor and malaise are felt, with great indisposition to bodily labor.  With a dry air these are not so noticeable.  The cause is evident; in the former case but little evaporation occurs from the skin, and the normal amount of moisture is not given off from the lungs, so that the body is not cooled down to such an extent as by dry air.  Sunstroke is probably the result, not only of the direct action of the sun’s rays, but partly from diminished cooling of the blood by want of evaporation from the lungs and skin.

The effects of temperature on man do not depend so much on the mean for the day, month, or year, as on the extremes, as, when the days are hot and the nights comparatively cool, the energy of the system becomes partially restored, so that a residence near the sea, or in the vicinity of high mountains, in hot climates is, other things being equal, less enervating than in the plains, as the night air is generally cooler.  It is commonly believed that hot climates are necessarily injurious to Europeans, by causing frequent liver derangements and diseases, dysentery, cholera, and fevers.  This, however, is, to a certain extent, a mistake, as the recent medical statistical returns of our army in India show that in the new barracks, with more careful supervision as regards diet and clothing, the sickness and death-rates are much reduced.  Planters and others, who ride about a good deal, as