THE RAT THEORY OF PLAGUE EPIDEMICS 



21 



My results show that : — 



(i). Acute rat plague is followed by epidemic plague. 

 (2). Chronic rat plague would appear to bridge over epidemic 

 plague. 

 An explanation of the occurrence of chronic rat plague, as a sequel 

 to an epizootic of acute rat plague, is by no means easy. From what 



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.S 1.5 22;'y 5 121:1 2(1 2 i!) 16 23 30 7 14 21 28 t II 

 July. August. Scptcnihar. Octobur. Noviiiil 



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.1 2 9 lfi23.'?0 7 14 21 28 4 11 IS 2,5 3 10 17 24 31 7 14 ! 

 Deccmher. Jivnunry. February. . March. , April. 



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1 28 A 1210 26 

 . May. 



Chart VII. 



has already been said, the continued passage of the B. pestis through the 

 body of the rat tends to render the organism less virulent. Therefore, it 

 is probable that a strain of the bacillus which excites acute rat plague 

 during the early passages, will only cause chronic rat plague during the 



(235) 



