144 OMENTAL PLAGUE chap. 



the guinea-pig. But it is different with the B. pestis 

 (virulent type) when bred in the black ship rat, for here 

 as a rule a B. pestis will be the result, which, tested on 

 the guinea-pig, behaves like an attenuated B. pestis, 

 inasmuch as even when injected subcutaneously it does 

 not cause acute but only subacute plague. 



The same explanation may also be applied to Hankin's 

 statement, to the effect that B. pestis passed through a 

 series of rats loses its virulence. As mentioned just now, 

 this is certainly not correct if expressed in this general 

 way, for it depends through which race of rats it is 

 passed. It is, however, incorrect when applied to the 

 guinea-pig, for in this animal there occurs no attenuation, 

 provided the race of B. pestis at starting is the right one 

 and the infection is made by subcutaneous injection. 



The above explanation would at the same time furnish 

 us with the possibility of understanding the reason why 

 transmission of plague introduced by ship rats to those 

 on shore takes, according to all accounts (see also 

 Dr. Ashburton Thomson's Reports on Plague in Sydney), 

 a considerable time for its eventual transmission to human 

 beings on shore. It is probable that the type of B. pestis 

 bred by those rats is the attenuated type 2, and therefore 

 it requires a particularly inflammable material, i.e. highly 

 susceptible human individuals, for starting human plague ; 

 but once having had access to a human being it again 

 may readily revert to its former virulent type, and 

 having access to other human beings (pneumonic forms, 

 septicsemic forms of plague) becomes rapidly disseminated 

 and takes effect also among less susceptible human beings. 



Plague ai'tificially induced in the Monkey. — When 

 the monkey (macacus) is injected subcutaneously in the 



