ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 259 



A moderately high temperature is most favorable to the breeding of 

 this pest; above 86° F. it declines. Moist, alluvial soils; the banks of 

 great rivers, such as the Nile and Euphrates; a warm, humid air; great 

 accumulations of putrefying animal and vegetable matter in the vicin- 

 ity of dwellings; dwellings surrounded by heaps of manure and almost 

 hermetically sealed — these are conditions favorable to the growth of 

 1)1 ague. Once started, it spreads by infection much after the manner of 

 typhus. Care for the purity of air in and around dwellings abolishes 

 plague altogether, as has been proved locally in the Himalayas and 

 generally in the retrogression of the disease from Europe. 



CHOLERA. 



Cholera is to a great extent a disease of air poisoning. It arises 

 from the soil iu certain districts of India, where it is endemic, and from 

 which it occasionally has the opportunity, through favoring climatic 

 influences and the movements of travelers, of invading temperate 

 regions, in which it may cause great mortality in a few seasons, but 

 can hardly establish itself permanently in the soil or water. It does 

 not, as was long supposed, travel from place to place through the air, 

 and has no epidemic existence beyond its breeding places apart from 

 human agency. The cholera microbe, the comma in all probability, 

 thrives in a damp, organically polluted soil, such as that of the delta 

 of the Ganges and the flat lands around Madras, Bombay, and Shang- 

 hai; of the valleys of the Brahmaputra, the Nerbudda, the Tapti, the 

 Indus, and the Euphrates, and in a temperature of from 25° to 40° C. 

 In the delta of the Ganges the temperature of soil and air appears to 

 be so favorable that it never dies down ; at Shanghai it regularly infects 

 the air and water after the heat of July and August. It is aerobic. A 

 freezing temperature prevents its growth, but does not destroy it. Kept 

 moist, it may live for months after growth has ceased ; dried for a few 

 hours, it dies. In temperate climates it is spread by the entrance into 

 water and air of the organisms derived from growth in the dejections 

 of cholera patients, some cases being only recognized as diarrhea, but 

 still being capable of spreading the poison. The destruction of the 

 dejecta is, therefore, the safeguard in all cases. The power of exten- 

 sion of cholera through the air alone in the neighborhood of cholera 

 patients where due hygienic precautions are observed is very small, 

 but every article used must be washed or sterilized. The general 

 atmosphere does not convey it either from person to person or from soil 

 to soil, unless, possibly, in rare cases and for a short distance. In fact, 

 free air, unless very humid, soon kills it. The atmosphere of the Gan- 

 getic delta, the chief endemic area of cholera, is remarkably damp. 

 There are probably a number of places in India where the soil is to 

 some extent infected, but where mischief arises only in certain seasons. 



The conditions of soil and air favorable to the growth and exhala- 

 tion of the cholera germ may be concisely summed up as follows; 



