214 OMENTAL PLAGUE chap. 



clumps having formed, and in one hour it was unmis- 

 takable, and practically most bacilli had aggregated into 

 loose masses. 



It follows from these experiments that after three 

 subcutaneous injections of guinea-pigs with large masses of 

 solid growth of sterilised plague bacilli the blood of these 

 animals acquired unmistakably the power to agglutinate 

 plague bacilli. 



The blood of one of these guinea-pigs was used for 

 an agglutination experiment on two different strains of 

 plague bacilli, the one derived from a plague rat which died 

 in a dock warehouse in Cardiff, the other from a plague 

 rat which died in Cape Town. In both these instances 

 the test (dilution 1 in 20 for half an hour) proved as 

 positive as with the strain of laboratory plague bacilli. 



(d) The same two guinea-pigs were again injected on 

 March 27 with about a platinum loopful of living plague 

 bacilli from an agar surface culture about seven weeks 

 old ; that is to say, they were injected with a com- 

 paratively small and presumably non-fatal dose of an 

 attenuated culture of living plague bacilli. This was 

 done because former experience (see my Eeport, 1896- 

 1897, p. 287) has shown that it is extremely difficult to 

 render guinea-pigs immune against largish doses of living 

 plague bacilli. As a matter of fact, both the above 

 guinea-pigs developed buboes in the course of the next 

 few days, and one animal (guinea-pig No. 2) was found 

 dead on the tenth day after the last injection. The other 

 animal recovered completely. Nineteen days after the 

 last injection the blood serum of this animal was tested 

 on salt emulsion of B. pestis (dilution 1 : 20), two different 

 strains being used — (a) the laboratory strain ; (b) a strain 





