ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 263 



as Western Bajpootana, are subject to malaria, although the water is 

 several hundred feet below the surface. But here the sand is found to 

 be damp a short distance below the surface, and probably the same 

 condition prevails elsewhere in sandy tracts where malaria is present. 

 The rainfall is scanty, but the great range of temperature probably 

 causes a good deal of dew-condensation on the sand. 



Sometimes, though rarely, rocky surfaces emit malaria, but probably 

 the habitat of the organisms in these cases is in clefts or disintegrated 

 rocky detritus. The efficiency of attack on the human body depends 

 in great measure on the concentration of the organisms within a few 

 feet of the surface of the earth in the evening hours, the difference 

 between day and night temperature, the high temperature of the soil, 

 and the suddenness of the fall of temperature. Although the strong- 

 est men in the best of health may be stricken, yet, in most malarious 

 countries, the avoidance of fatigue, of indigestion, and of any chilling 

 of the surface of the body, is an important safeguard. The conditions 

 in which malarious germs are emitted from the soil and concentrated 

 in the nethermost strata of the air are further considered in relation to 

 the emanation of vapor from the earth and the deposition of dew. 



YELLOW FEVER. 



Yellow fever results, in all probability, from a fungoid or microbic 

 growth, but the particular microbe concerned has not been certainly 

 identified. It prevails habitually in the West Indies and on the coasts of 

 the Gulf of Mexico, and these have been regarded as the original breed- 

 ing grounds. But it has also long been endemic on the west coast of 

 Africa, especially at Sierra Leone. It is easily capable of transporta- 

 tion, especially in the case of particular outbreaks and in particular 

 seasons, and it has in several years, like cholera, attained almost a 

 world-wide prevalence. When transplanted to favorable places (and 

 these are mostly seaports with very poor sanitary conditions) it takes 

 root and breaks out in succeeding years as if it were multiplying on 

 the polluted soil. As a matter of fact, it thrives on damp organically 

 contaminated soil, on the walls of houses, and on the wood of ships, in 

 foul holds. It haunts the vicinity of drains, banks of rivers occasion- 

 ally dry, harbors, and crowded rooms or houses. The manner of its 

 growth a good deal resembles that of cholera, but its areas of preva- 

 lence are smaller, and it is more largely communicated through the air, 

 each case of yellow fever becoming a focus of prevalence in tropical 

 and foul conditions. It requires a high temperature for its propaga- 

 tion, and is arrested, but not destroyed, by frost. Strangers are much 

 more liable to attack than residents, but residents are not always 

 immune. The living cause of the disease clings with great tenacity 

 to ships, walls, etc., for a long time, and is conveyed, in very many 

 instances, by the air to persons who approach the infected object. The 

 organic poison seems to multiply outside the body, upon foul surfaces, 



