96 "PURE MIXED CULTURES" OF AMCEBA 



resulting culture plated out. Three types of 

 colonies were obtained, and from each of these 

 nutrient agar slope cultures were prepared, and an 

 analysis of each of these was carried out. The three 

 bacteria isolated in this way were B. fluorescens 

 liquefaciens, B. brmmeum, and B. Jlavo coriaceus 

 (fig. 28). The colonies of the liquefying fluorescens 

 were not recognised as different from those of the 

 non-liquefying variety. The last of these bacteria 

 is very slow-growing on plain 2-per-cent. agar at 

 the room temperature, and in subcultures was 

 quickly crowded out by the other two. These 

 were difficult to get rid of until hydrochloric acid 

 was tried. Slope cultures treated with this reagent 

 (2 per cent.) for forty-eight hours, and thoroughly 

 washed, were found sterile to nutrient agar slopes 

 at the room temperature and 37 C. The cysts 

 were put into pure culture with B. fluorescens 

 liquefaciens, cultures of this being treated again 

 with HC1, and the cysts transferred to a culture 

 of the non-liquefying variety on a gelatin medium. 



The second series of analyses was carried out on 

 a supposed pure mixed culture prepared by the 

 plating-out method, and showed the presence of two 

 bacteria, namely, B. fluorescens liquefaciens (fig. 29) 

 and B. proteus vulgaris (fig. 30). The necessity 

 for a complete analysis is indicated by the fact 

 that the differentiation of these was only finally 

 made out by means of a nutrient broth culture, for 

 although two types of colonies appeared on the 

 plates, their morphology and reactions were very 

 similar. The full report is subjoined : 



Plates were prepared by pouring, and two types 

 of colony were obtained, A and B, viz. : 



