1917] The Ecology of Bubonic Plague 201 



5. Lahore City. — It is 700 ft. above sea level. It is not 

 within the hot mansoon belt. The rainfall is slight, amounting 

 to about 20-25 inches, and occurs chiefly from July to September. 

 Some rain falls at times during January and February. From 

 November till March the daily mean temperature is below 

 70° F., in January as low as 54° F. The remainder of the year 

 is above 70° F., from May to August as high as 85° F. to 95° F. 

 The average diurnal range is 27.5° F. (April to May it is 32.5°, 

 and October to November it is 35°.) 



Plague epidemics occur from March to May. There is a 

 tendency to recrudescence during the winter months. Plague 

 mortality rises rapidly as the humidity recedes, but as soon as 

 the humidity begins to rise, the epidemic is quickly terminated. 



6. Rawalpindi City and Cantonments. — Situated at the base 

 of the Himalayas, 1,700 ft. above sea level, it has an average 

 diurnal range of from 20° to 30° F. Its hot weather comes from 

 May to August, with a mean temperature of from 80° to 92° F. 

 The rainfall, mostly from July to September, amounts to but 30 

 or 40 inches. About eight inches of rain falls during the winter 

 season, January to April. 



The plague epidemic is from September to November, with 

 slight recrudescence practically throughout the year. The 

 major epidemics rise rapidly as the humidity recedes. 



7. Summary: The authors of the several articles from 

 which these notes were taken, draw certain conclusions, which 

 in brief are: That a temperature of 85° to 90° F., or one of 

 50° or less, are very unfavorable to plague. This holds true 

 for Bombay City, but does not for Poona and other cities. 

 The truth of the matter is that no one factor alone may exert 

 such wide influences, but that it is rather a resultant of several 

 factors — in this case it is humidity. When plague mortality 

 and humidity are placed on the same chart, it becomes at once 

 evident that there is a direct relation between the two. 



We shall see a little later on, that the severity of an epidemic 

 of bubonic plague bears a direct ratio to (a) flea prevalence and (b) 

 to humidity. 



B. Fleas. 



The investigators in India report that a temperature above 

 80° F. affected the conditions to which the bacillus was subjected 

 in the flea's stomach. At high temperatures the bacillus 



