206 OEIENTAL PLAGUE chap. 



attempted to be removed, the growth is drawn out along 

 with it as a slimy thread. When an attempt is made to 

 emulsify such growth the utmost that can be achieved by 

 shaking it up in broth or salt solution is a breaking up 

 into larger or smaller flocculi, on account of the presence 

 of the gelatinous interstitial substance by which the 

 bacterial cells are agglutinated. To use, therefore, for the 

 agglutination test an emulsion in which from the outset 

 there are present small and large masses, would not only 

 be useless, but might be altogether misleading. While 

 these difficulties are found with broth cultures and with 

 cultures on agar and on serum, they apply in much less 

 degree to cultures of B. pestis on the surface of gelatine ; 

 for on this medium the B. pestis forms a growth which 

 is fairly dry and not of a viscid nature, although here also 

 the bacilli are intimately aggregated. A fairly uniform 

 emulsion can, however, usually be obtained from a surface 

 gelatine culture by shaking up a particle of the growth in 

 bouillon or in salt solution. By shaking up gelatine 

 growth in distilled water an excellent emulsion can also 

 be rapidly established. Similarly, by shaking up a recent 

 agar culture in salt solution an emulsion is made which, 

 filtered through filter-paper, forms a workable fluid. 



First as to the bouillon and salt emulsion of gelatine 

 culture of the bacillus. 



After a considerable amount of experimentation with 

 gelatine cultures, recent and old, I have found that 

 gelatine cultures of a recent or fairly recent date, e.g. 

 established from two to ten or twelve days, are most 

 suitable. A particle of the growth is removed with a 

 platinum needle or platinum loop and distributed by 

 agitation in, say, salt solution so as to render the fluid 



