l8 QUATERCENTENARY STUDIES IN PATHOLOGY 



Further remarks in regard to the curve appear unnecessary, as a 

 comparison of this chart with the foregoing will clear up any doubtful 

 points. 



II.— The Bridging of Epidemic Plague during the intervals 

 1902.'03 and '04. 



In almost all plague-infected countries, the epidemic is found to be 

 most prevalent during certain seasons of the year. In Hong-Kong, these 

 epidemics rage from March to July inclusive. In other countries plague 

 appears during the colder seasons of the year and vice versa. The 

 reasons for such a seasonal recurrence of plague are by no means obvious, 

 and a consultation of current plague literature helps one but little. At 

 the present time, climatic influences would appear to have lost much of 

 their significance. Plague epidemics occur in Siberia as well as in the 

 equatorial regions, and carefully prepared records of sunshine, humidity, 

 and rain shows these factors to have little determining influence on the 

 occurrence of plague epidemics. All that can be said in regard to 

 climate is that it may exercise an indirect influence on the course of the 

 infection. 



During the interval between the end of one epidemic and the first 

 cases of the succeeding epidemic, human plague is, to all intents and 

 purposes, non-existent. A few cases do occur, but these are of no great 

 practical significance, apart from the fact that they help us to remember 

 that with the decline of the last epidemic our sanitarians have, in all 

 probability, not yet succeeded in stamping out the disease. 



Further, the reasons for the outbreak of erratic cases of human 

 plague are by no means clear. 



To begin with, little or nothing is known in regard to the history of 

 epizootic plague in rats through a number of years. Many authorities 

 believe that rat plague dies out on the decline of human plague. 



Two charts have been prepared, showing the relations existing 

 between epizootic and epidemic plague during the period, July, 1902, to 

 June, 1903, inclusive (Chart VI.) ; and during the period, July, 1903, to 

 May, 1904, inclusive (Chart VI I.). These show clearly the condition of 

 affairs which obtains in an endemic plague centre like Hong-Kong. In 

 both charts the epidemic vanishes, but the epizootic persists with a low 



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