Winter and Summer Diseases of the Temperate Zones.—It is natural that such marked seasonal and such sudden weather changes as ours should be reflected in the character, distribution and frequency of the diseases which are found in these zones. Diseases of the respiratory system, bronchial and rheumatic affections, diseases that result from colds and chills, pneumonia, bronchitis, influenza, diphtheria, whooping cough, are all common in climates with sudden marked temperature changes, especially if these changes are accompanied by cold, damp winds. These diseases are also most frequent in the winter months, when the weather changes are more common and more severe, and when, in consequence, the vitality of the body is lowered and its power of resistance against the attack of the disease germs is weakened. A greater prevalence of diseases of the respiratory system, catarrhs and rheumatic affections in cool, moist weather, with sudden changes, has been shown by Weber, and several investigators have found a higher mortality after a greater variability of temperature. Many contagious or infectious diseases, such as diphtheria, influenza, measles and scarlet fever, for example, are also more common in the colder season, not because the lower temperatures are the direct controlling factor, but largely because the colder weather drives people indoors; houses and buildings generally are less well ventilated; more clothing is worn, less attention is paid to personal cleanliness and there is increased opportunity for contagion, especially among the poorer classes. Obviously, these are indirect effects of meteorological conditions.
In the warmer months, fevers and diseases of the digestive system, diarrhœa, malaria, typhoid fever, are prevalent. Thus there are usually two maxima of mortality: one in the colder season, when the changeableness of temperature is greatest, chiefly due to respiratory diseases, and another in the warmer months, largely due to infant mortality from disorders of the bowels.
Climate and Man: General.—Let us turn now to some larger, more general, relations of climate and man. Man's climatic environment affects him in many ways. His clothing, dwellings, food, occupations and customs; his physical and mental characteristics; his systems of government; his migrations; his history—all are affected to a greater or less degree.
Civilized man protects himself more or less successfully against unfavorable climatic features. Thus, there is a gradual transition from the primitive shelter made of branches of trees, of skins or leaves, to the permanent and highly elaborate modern building, which is both heated and cooled artificially. There is also a transition from the primitive and scanty clothing made of leaves or bark, where trees grow, or the skin of an animal, where trees are lacking, or where warmer clothing is needed, to the manufactured or perhaps imported garment of wool, cotton or silk. Again, there is the increasing variety of food,
