2 5 4 THE POPULAR SCIENCE MONTHLY 



longer sought directly in meteorological conditions, but in the effects, 

 more or less direct, of these conditions upon the microorganisms 

 which are the specific cause of the disease. Atmospheric conditions 

 may help or may retard the development of the microorganism, and 

 may strengthen or weaken the individuals' power of resistance. Winds 

 used to be regarded as the chief agents in spreading epidemics : now it 

 is known that disease can not be carried far by winds, for the micro- 

 organisms do not long maintain their power in the free air and under 

 the sun. Eain has been supposed directly to control the distribution 

 of disease: now we believe that precipitation acts only indirectly, 

 through drinking-water, or through its control over the dust in the 

 air. Dust from dry soil, and from city streets, may contain the germs 

 of infectious diseases, and aggravate affections of the respiratory 

 organs. 



Geographical Distribution of Disease. — The scheme of classifying 

 disease geographically, on a broad climatic basis, is attractive, but not 

 very satisfactory. For, on the one hand, many diseases are practically 

 universal in extent, showing great independence of climate, and, on the 

 other, the history of many diseases is still in the making. In spite of 

 this complexity, however, certain broad statements may be made, useful 

 in enabling the layman properly to coordinate his ideas on the subject, 

 and fairly accurate within reasonable limits. 



Tropics: General Physiological Effects. — Tropical monotony of 

 heat is associated with high relative humidity, except over deserts and 

 in dry seasons. The air is therefore muggy and oppressive. This 

 "hot-house air" has an enervating effect. Energetic physical and 

 mental action are often difficult, or even impossible. The tonic effect 

 of a cold winter is lacking. These conditions have certain fairly well- 

 established physiological effects, which, combined with less power to do 

 work, greater fatigue from work, and lowered vitality, render the body 

 less able to resist disease. 



Hygiene in the Tropics. — Under the peculiar conditions of tropical 

 climates, the resident who comes from a cooler latitude should take 

 special precautions regarding his mode of life and personal hygiene. 

 A rational, temperate life, especially the avoidance of alcoholic ex- 

 cess; regular exercise; non-fat-producing food; clothing suited to the 

 climate; all possible sanitary precautions; protection against mosqui- 

 toes; frequent change of climate by returning to cooler latitudes — all 

 these are important. It seems like a contradiction, but it is a fact, 

 that the danger of becoming chilled in the tropics is very great and 

 must be carefully guarded against. General Wolseley is reported to 

 have said of the tropics, "not to get cold is to avoid almost certainly 

 all the causes of disease," and a recent writer has well said that these 

 words should be inscribed on the walls of all barracks in the tropics. 

 The situation may be summed up in this rule : " Eespect the sun, and 



