v PLAGUE IN THE EAT 97 



pigs and rats which had been injected with plague 

 cultures which in the course of many transferences on 

 gelatine or agar had become naturally attenuated. This 

 natural attenuation by continued subculturing of B. pestis 

 is a well-known fact. It does not, however, involve all 

 races to an equal degree. Thus, for instance, the strain 

 of B. pestis derived from the fatal case in London 

 Docks in October 1896, which has been kept up in 

 my laboratory on gelatine subcultures, was in 1903 

 still possessed of a fair degree of virulence ; likewise the 

 strain of B. pestis derived from the Cardiff rat when 

 taken from gelatine culture is still lethally active when 

 injected in small doses into guinea-pigs and rats. It is 

 different with a strain of B. pestis derived from the lung 

 of a plague case dead at Hull (s.s. Friary). Of this 

 strain a considerable dose of gelatine culture has to be 

 injected in order to produce general infection and death. 

 With a gelatine culture of the B. pestis of the Bristol rat, 

 or with a strain derived from the Oporto outbreak, not 

 even half a culture injected intraperitoneally can be relied 

 upon to cause fatal issue in the guinea-pig. A similar 

 remarkable and rapid loss of virulence was observed in 

 regard of a strain (L.P. No. II.) derived last year from a 

 case of human plague in a London dock, from an Indian 

 native. It follows therefore that conspicuously degenera- 

 tive forms observed in culture or in animals abortively 

 infected afford no indication of a radical difference between 

 bacilli which are and those which are not B. pestis. 



The cultures already referred to as forwarded by 

 Dr. Edington were at once, on receipt, used for plate 

 cultures on agar and for injection into the peritoneum of 

 guinea-pigs. 



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