viii AGGLUTINATION OF B. PESTIS 209 



bacilli for the object of making the agglutination test are 

 therefore altogether useless. More than that : I have 

 shown (The Lancet, February 16, 1901) that the addition 

 of sterile bouillon to a good and otherwise permanent salt 

 emulsion of B. pestis, in the proportion of 1 to 20 or even 

 1 to 40, causes within fifteen to thirty minutes distinct 

 agglutination. I am disposed to think that the unreliable 

 and unsatisfactory agglutination results obtained by some 

 observers with the B. pestis have been due to their using 

 bouillon emulsions, such, for instance, as are very useful 

 in the case of B. typhosus, Vibrio cholera, and other 

 microbes. 



Another kind of emulsion to be avoided in testing for 

 agglutination with the plague bacillus is the watery 

 emulsion. The first experiments that I made with a 

 watery emulsion of gelatine plague culture were remark- 

 able and deserve to be described in detail. Kemoving a 

 particle of the growth from a week's old gelatine culture 

 (slanting surface) and placing it in sterile distilled water, 

 it was noticed that even a comparatively slight agitation 

 produced an excellent emulsion ; very soon neither with 

 the unaided eye nor with the microscope could any 

 aggregated mass be recognised, the bacilli formed indeed 

 a uniform excellent emulsion. The blood serum of an 

 animal which I had previously (and also afterwards) 

 ascertained to possess distinct agglutinating power in 

 dilution of 1 in 20, was added in the same proportion (viz. 

 1 in 20) to the above watery emulsion of plague bacilli. 

 The result was quite unexpected, inasmuch as there 

 occurred complete and striking agglutination within five 

 minutes. It was, however, noticed that on adding the blood 

 as such (1 part) to an equal amount (20 parts) of water 



