1917] The Ecology of Bubonic Plague .199 



It appeared to me desirable to learn if such ecological 

 relations could be traced with any of the other diseases directly 

 transmitted by arthropods, especially bubonic plague. World's 

 commerce is becoming so extensive that very soon it will 

 become imperative to open up territories now almost closed to us 

 on account of the presence in them of plague. Quarantine 

 measures are efficacious, but they are also quite expensive 

 because much time is lost. We must fight the plague wherever 

 it occurs. We must get rid of it. This can be done and the 

 cost is relatively low. The study of the ecological relation in 

 plague should reveal to the sanitary officer not merely the kinds 

 of measures he must adopt in order to obtain quick and telling 

 results, but also when to employ these measures, and just where 

 they must be used in order to obtain maximum efficiency. 



I found very valuable data on bubonic plague in the many 

 "Reports on Plague Investigations in India," published in the 

 Journal of Hygiene. During twelve years plague claimed five 

 million victims in India. A trifle over two a minute died during 

 the year 1907! The chart appended to my notes is taken from 

 one of these reports. Other regions where plague is endemic 

 may have a different set of conditions from those in India. 

 These conditions must be well known before the inter-relation- 

 ships between rat, flea and plague are properly understood and 

 correlated. 



A. Plague and Climate. 



1. Bombay City. — Its climate is hot and dry, the daily 

 mean temperature being from 70° to 80° F. The average 

 diurnal range in only 12.5° F. The S.W. monsoons appear 

 from May to October, and they bring the rains. These rains 

 are heaviest from June to August. The N-E monsoons, 

 which blow from November till April, bring very little or no 

 rain. 



The plague epidemic begins in January, rises gradually 

 until it reaches its maximum in March, then declines to a 

 "normal" about the middle of May. Charts which were kept 

 for ten consecutive years show plague mortality lowest when 

 humidity was highest, Qune to September), and that an almost 

 automatic recession from the maximum takes place as soon as 

 the humidity begins to rise. The mean temperature at the 

 beginning of the rise is from 72° to 75° F., but as soon as it 



