208 ORIENTAL PLAGUE chap. 



to warn all observers from relying on the agglutination 

 test with emulsions of non-motile bacteria in which is 

 involved similar liability to mere sedimentation. At any 

 rate, my experiments on agglutination with emulsion of 

 B. pestis by sedimentation have given very unsatisfactory 

 results, and I have therefore abandoned them and have 

 relied solely on the agglutination test under the microscope. 

 In using this it is necessary to subject a large drop of the 

 mixture of emulsion and blood serum to microscopic 

 examination, so as to give the suspended bacilli a fair 

 chance of coming together. If the test be made by 

 covering a small drop of the mixture deposited on a glass 

 slide with a covering glass, and thereby exposing the 

 bacilli only in a very thin layer, there would be no chance 

 given to the non-motile (plague or other) bacilli, if any 

 were present, to respond to the agglutination force. 



A further point in connection with these experiments 

 which needs to be insisted on is that the agglutination 

 test is valueless with bouillon emulsions. If a good and 

 workable bouillon emulsion of B. pestis is prepared from a 

 gelatine culture in the manner already described — an 

 emulsion, for instance, in which the great majority of the 

 bacilli are well isolated, and in which perhaps only here 

 and there small groups of two or three bacilli occur — if, I 

 say, such bouillon emulsion is then watched under the 

 microscope it will be found that agglutination occurs in a 

 comparatively rapid way. Clumps of fair size are formed 

 within ten to fifteen minutes or even less, so much so that 

 in some experiments with no addition of any material 

 whatever " complete " agglutination in fairly large masses 

 and disappearance of all single bacilli as such occurs in 

 fifteen to thirty minutes. Bouillon emulsions of plague 



