THE RAT THEORY OF PLAGUE EPIDEMICS 9 



The research is even comph'cated to a much greater degree in regard to 

 the diagnosis of the presence of plague bacilli in rats. 



Rats suffer from a large number of septicaemia diseases. These 

 diseases frequently break out amongst them in epizootic form with a 

 heavy mortality. 



Among the many micro-organisms causing these epidemic diseases 

 may be mentioned B. Danysz, the B. of Schilling, etc. Other micro- 

 organisms, such as the B, of fowl cholera, B. of swine plague, etc., are also 

 pathogenic for rats. Morphologically and tinctorially all the above- 

 mentioned micro-organisms resemble the B. pestis. Therefore, it is 

 evident that even though plague is prevalent among the rats in any 

 particular city, one has to be on guard for the possible occurrence of 

 other epidemic diseases which might account for an increased death rate 

 at any time among them. 



Since the year 1902, this systematic bacteriological examination of 

 rats has gone on. The following figures give approximately the number 

 of rats collected and examined, with the total found plague-infected per 



annum. Year. No. examined. No. found infected. 



1902. 117,839 2015 



1903. 101,056 3744 



1904. 21,907 993 



Having established bacteriologically the existence of Rat Plague in 

 Hong-Kong, the examinations were carefully continued, and the amounts 

 of the epizootic and the epidemic noted week by week. In this way it 

 has been found possible to plot curves of each form of the disease. 

 Annual charts, representing the weekly fluctuations in the epizootic and 

 the epidemic, have been prepared. In these, the epizootic is marked by 

 an uninterrupted line, the epidemic by a dotted line. 



In dealing with the results which have been obtained through 

 following the courses of the epizootic and the epidemic, I propose to 

 divide my investigations into the following divisions : — 



I. The History of the Course and Relations of Epizootic and 

 Epidemic Plague in Hong-Kong — 

 {a) during the year 1902. 

 (b) during the year 1903. 

 {c) during the year 1904. 

 H. The Bridging of Epidemic Plague during the intervals i902-'o3 

 and '04. 



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