262 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



mixture with fresh air, and there is some evidence to show that oxida- 

 tion by the air in running water has a good effect where the noxious 

 matter is largely diluted and the stream pure. In London, New York, 

 Paris, Berlin, and perhaps the majority of places in the northern tem- 

 perate zone, typhoid fever is most prevalent in the late summer or 

 autumn, when the ground at a little depth, and water in shallow wells, 

 are at their highest temperature. In India it occurs mostly in the hot, 

 dry months before and after the rains, and may in part be attributed 

 to the wind blowing up the dust of filth deposited in the fields, but 

 chiefly to the same conditions as prevail in England and to the intro- 

 duction of the virus, often from slight and unsuspected cases. 



The great majority of houses in civilized places resemble inverted, 

 slightly ventilated bell jars, connected with a system of pipes on which 

 deadly organisms may grow, and from which they may be conveyed by 

 the poisonous gases to the bodies of the inmates. It should be a pri- 

 mary object to make the entrance of these gases difficult and of the 

 outer air easy. The bacillus concerned in typhoid fever is probably 

 widely diffused, but, whether often present or not in an innocuous form 

 in the human intestines, does not attack life where air and diet are pure. 

 With the aid of impure air from drains, middens, and foul sinks it 

 acquires deadly power. Cleanly disposal of refuse and abundance of 

 fresh air are the great securities against this disease. 



MALARIA. 



Malaria is the most general, constant, and destructive of endemic 

 diseases in tropical climates and over a very large proportion of the 

 inhabited globe. Millions die of it every year in India, and in Africa 

 and South America it is terribly prevalent and fatal. Vast numbers of 

 people are crippled and diseased for life in consequence of the fever, 

 and in many districts the whole population looks debilitated and anaemic. 

 It depends on the emission of living organisms, probably anioebiform, 

 from warm, damp soil, rich mold, sand, or other suitable ground con- 

 taining a little organic matter. It haunts open and narrow valleys, 

 dried water courses, the country at the foot of many mountain ranges, 

 sandy coasts in certain climates, mangrove swamps, deltas, marshes, 

 and even in certain districts dry, sandy plains at a considerable eleva- 

 tion. The organism appears to exist either in an active or latent form 

 in nearly all hot countries where the soil contains sufficient organic 

 matter, and that need not be much. Where soil is efficiently drained, 

 naturally or artificially, malaria is rare or absent; and where irrigation 

 works increase the dampness of the soil, there also malaria increases 

 or develops itself. Cultivation, with the exception of rice growing, 

 in general diminishes or abolishes malaria within the area cultivated. 

 Lowering of the water level and aeration of the soil reduce malaria 

 notably. Drainage in East Anglia has almost extinguished ague, which 

 is a similar or the same disease. Some sandy, semidesert districts, such 



