CLIMATE IN SOME OF ITS RELATIONS TO MAN 253 



atmospheric conditions an explanation of the occurrence of disease. 

 Many fairly obvious facts naturally point to some relation of cause 

 and effect in this matter. Some diseases are found principally in 

 warmer climates; others seem to prefer the colder. Some are usually 

 more active in the warmer, or the drier months ; others have shown the 

 contrary relation. High altitudes are free from some of the diseases 

 which prevail near sea-level, and have certain favorable climatic char- 

 acteristics long recognized in the treatment of disease. In the case of 

 other diseases, again, altitude has no effect. Dry climates, especially 

 deserts, whose air is usually exceptionally pure and aseptic, are gen- 

 erally healthful, and are beneficial in many cases where mountain 

 climates are too stimulating. The climates within forested areas have 

 proved especially favorable in cases of phthisis. Ocean air, pure and 

 dust-free, with its saline constituents and equability of temperature, is 

 beneficial to most persons as a moderate tonic and as a restorative in 

 many illnesses. Winds are active ventilating and purifying agents 

 where population is congested. Fogs and clouds, by cutting off sun- 

 light, weaken one of the best agents in promoting health, for sunlight, 

 in the words of Dr. Sternberg, is " one of the most potent and one of 

 the cheapest agents for the destruction of pathogenic bacteria." In 

 London, a higher death-rate follows a long fog, but this may result 

 from the lower temperature during the fog, and not from any direct 

 effect of the fog itself. 



A Complex Subject. — Facts like these naturally prejudice one in 

 favor of a causal connection between atmospheric conditions and dis- 

 ease. Nevertheless, such studies have often led to very contradictory 

 conclusions. Some of the difficulty arises from untrustworthy statistics, 

 but most of the disagreement comes from the fact that not only may 

 each of the different weather elements have some effect in the produc- 

 tion of the disease, but so many other factors are concerned in the 

 matter that confusion and contradiction in the conclusions reached are 

 inevitable. Sanitation, food, water, habits, altitude, character and 

 moisture of the soil, race, traffic and other controls, serve to compli- 

 cate the problem. In most studies of climate and health some, or even 

 many, of these factors have not received attention. Overcrowding 

 under unhygienic conditions, especially indoors during cold weather, 

 and traffic by rail, steamship, caravan or on foot, are often more im- 

 portant than climate. The frequent escape of mountain, of desert and 

 of polar peoples from epidemics is to be attributed in most cases to the 

 smaller chance of importing disease because of little intercourse with 

 the outside world, and of spreading it, when imported, because of the 

 scattered population. It may be noted, however, that crowding indoors 

 in winter, and the sparseness of population just referred to, are them- 

 selves climatically controlled. 



Climate, Microorganisms and Disease. — The cause of disease is no 



