x MODES OF DESTRUCTION OF B. PESTIS 281 



natural conditions? That is to say, provided a certain 

 race of B. pestis is restricted to carrying on its existence 

 in outside nature, and is prevented from rinding entrance 

 into an animal body, in which, like other non-sporing 

 microbes, it might be able to again regain or enhance its 

 virulence — in other words, provided the B. pestis is 

 doomed to live as a saprophyte, and* is prevented from 

 resuming its parasitic existence — might this not have the 

 result that by and by it would altogether cease to be 

 possessed of infective power for the animal, body ? The 

 experiments which we have mentioned of type 2 certainly 

 seem to warrant such an assumption. Assuming that 

 this is possible in nature, we could understand how B. 

 pestis (in a concrete plague case), when introduced into 

 a locality in which it is not endemic, if debarred by 

 preventive sanitary measures from gaining access to a 

 further human being, would, owing to the saprophytic 

 conditions to which under these restrictions it would be 

 doomed to live, soon become deprived of all further 

 infective power. This would particularly apply to the 

 rat type bacillus (type 2), which, rapidly losing its 

 virulence altogether, would equally rapidly cease to be 

 infective. The B. pestis is not particularly selective in 

 its nutritive materials ; it, like, for instance, the Proteus 

 vulgaris, can grow almost in any medium containing 

 albuminous materials ; it can grow well in neutral, in 

 alkaline, and even in slightly acid materials — that is to 

 say, it can maintain its existence in most localities and 

 in most ordinary materials of filth in which Proteus, 

 Staphylococci, B. coli, B. typhosus, and Vibrio cholercB 

 can exist and multiply, particularly when the medium is 

 in a solid form. There is no reason to suppose that B. 



