DISEASES, DISTRIBUTION OF. It is generally known that the different regions of the earth are subject to diseases deriving their character from local circumstances and conditions, such as latitude, climate, the chemical quality of the soil, elevation of the land above the sea-level, variation of temperature, water distribution, character of the vegetation, and the peculiar habits of the people. The science of nosography in this aspect, however, did not receive much attention before the beginning of the present century, and is still comparatively undeveloped, though something has been done in the way of discovering and classifying facts. It is known that tropical regions are the homo of malarial fevers, cholera, and hepatic diseases. This is due in part to the damp soil and decaying vegetation, particularly in the river valleys. The yellow fever of the Mexican gulf, though often aggravated by other conditions. doubtless originated pri marily from this cause. In the more temperate zones, typhus, typhoid, intermittent, and scarlet fevers are found. They are, however, for the most part, not so much endemic as epidemic. In the northern hemisphere, n. of the tropical zone, catarrhal diseases prevail, while in the corresponding zone of the southern hemisphere they are unknown. Intestinal catarrh prevails, however, to a considerable extent in some parts of the intertropical regions. Nosologists are as yet unable to explain why some diseases prevail alike in widely different latitudes; for example, rheumatism in warm and dry as well as in cold and wet regions; and leprosy in Greenland, Norway, and Iceland, as well as in the tropics. In some eases, hilly regions are ravaged by fevers, while in the
intervening valleys fevers seldom occur. The cultivation of the soil, sometimes essen tially modifies the character of the malarial diseases. The destruction of forests often results in the introduction of diseases unknown before. Indeed, as a general rule, living vegetation tends to preserve health, while decaying vegetation is a prolific source of dis ease; but the modifications of this law are very little understood. Defective drainage, natural or artificial, is also a common source of disease, especially in, cities and thickly settled towns. The personal habits of races and communities in respect to diet and cleanliness, exert a wide influence upon the public health. Europe, on the whole, pos sesses the requisite conditions of health in greater perfection than any other quarter of the world. The rates of mortality from diseases of the lungs are greater in northern than in southern latitudes. This is illustrated by the prevalence of consumption in the north-eastern portion of the United States. Fevers are more prevalent in the southern than in the northern states. Malarial fevers are especially fatal in the southern regions of the country. They are infrequent, however, where pine forests abound. Knowledge on this subject, as yet fragmentary, is slowly increasing.