1907.] Bacteria of the Typhoid-coli Group, etc. 333 



Digitalin and stro- Gas always small, acid production often well marked. 



phanthin. 

 Coronillin, gratio-^ 



lin, baptism, >Acid and gas usually slight and inconstant. 



adonidin. J 



Phloridzin. "No gas production, acid formation slight. 



Colour changes are observed in the case of certain glucosides, the most 

 striking being the following. 



Media containing conifer in often turn yellow or orange even although no 

 apparent fermentation has taken place. Arbutin-containing media 

 frequently turn brown when the cultures are old and alkaline. This is quite 

 independent of any sign of fermentation. 



Syringin media turn to a bright pink colour when fermented. In some 

 instances, however, the colour is pale. 



Amygdalin media turn lemon yellow in old alkaline cultures, showing no 

 fermentative change. 



Phloridzin media inoculated with B. capsulatis, B. cloacae, B. pneumoniae, 

 B. lactis aerogenes, and Bacilli Nos. 30, 31, 32, 33, 38 and 41, show a bright 

 brick red colour. 



Plumierid becomes dark green in old alkaline cultures of B. lactis aerogenes, 

 and the same may occur to a less extent with other micro-organisms. 



The results quoted above seem to show that there is no sharp line of 

 demarcation between the various sub-groups of lactose fermenting micro- 

 organisms. It is true that nearly all the bacteria tested show slight 

 individual characters, but they are so closely allied to each other that 

 attempts to group them according to their lactose, dulcite, and saccharose 

 fermenting powers must be regarded as artificial. 



It seems, therefore, probable that the separate micro-organisms in the 

 various sub-groups are not to be regarded as distinct species, but as varieties 

 or hybrids of one or more species. If this be so, one might expect them to 

 be constantly varying, losing old characters and gaining new ones according 

 to the conditions under which they are grown, and it was with the object of 

 testing this hypothesis that further series of experiments were undertaken. 

 In the first place attempts were made to hybridise such organisms as B. coii 

 and B. typhosus, but owing to technical difficulties no conclusive results were 

 obtained. 



Attempts were then made to produce variations in the pure cultures of the 

 18 test types of micro-organisms, the method employed being to grow 

 each micro-organism for a succession of generations in a fluid medium 

 containing a sugar which it had failed to ferment, the object being to see 



2 b 2 



