viii AGGLUTINATION OF B. PESTIS 213 



colonies of B. pestis. Each animal received sub- 

 cutaneously the whole growth covering the surface of one 

 agar tube (6 centimetres by 2 centimetres). 



(b) The same two guinea-pigs were reinjected sub- 

 cutaneously on February 28 (ten days later) with' exactly 

 the same kind and same amount of sterilised culture. 



On March 11 (i.e. eleven days after the second injection) 

 blood of both guinea-pigs was withdrawn, allowed to clot, 

 and test was made with the serum on salt emulsion of the 

 laboratory B. pestis from gelatine culture, the dilution 

 being 1 in 20. 



[It is to be understood that in all experiments 

 (without exception) of agglutination of emulsion of plague 

 bacilli a control specimen was made of the emulsion alone 

 without the blood, so as to make sure that in the 

 particular emulsion agglutination did not occur spon- 

 taneously. Such has taken place in few instances for 

 reasons unknown and undiscovered. In such an instance 

 the experiment with the blood was rejected and repeated 

 on a subsequent day.] 



In ten to twenty minutes there was an indication of 

 the formation of small clumps. In one hour the number 

 and size of the clumps had increased ; but altogether the 

 agglutination was slight and not very pronounced. 



(c) The same two guinea-pigs were therefore re- 

 inoculated on March 11 with the same amounts and the 

 same kind of sterilised plague culture as in the previous 

 instances. 



On March 27, that is sixteen days later, the blood serum 

 of these two guinea-pigs was again tested on salt emulsion 

 of B. pestis (from gelatine culture), dilution 1 in 20. In 

 thirty minutes the agglutination was distinct, some largish 



