VARIATIONS IN TYPHOID BACILLI 319 



daughter colonies. The writer believes that this method deserves 

 a much more extended use in bacteriology than it has hitherto 

 received. It seems likely that one could employ it to determine 

 whether other substances besides sugars, for example, certain 

 amino-acids, are utilized by the bacterium in question as a food, 

 and in this way obtain a more accurate knowledge of the metabo- 

 lism of the organism and possibly important diagnostic distinc- 

 tions also. 



By investigating a large number of strains of Bad. typhosum, 

 using broth fluid and soHd media and extending the period of 

 observation over several weeks time it was observed that the 

 behavior of many strains toward certain sugars varied widely 

 from that of other strains. The slow fermenters of xylose 

 resemble the mutations of the higher plants first described by 

 de Vries, more closely than some of the other variants considered 

 in this paper because they retain their characteristics quite 

 constantly (for several years at least), so long as they are not 

 grown in media containing xylose; all such strains investigated 

 by us, with one exception, could be trained by long continued 

 cultivation in xylose-media to produce acid in xylose broth in 

 twenty-four hours like the typical Bact. typhosum. Furthermore, 

 all of these slow fermenters, including the one that never produced 

 acid in xylose-broth for us, showed daughter colonies on xylose 

 agar; hence we were aware of the fact that these strains could 

 utiUze xylose as a food-stuff long before this had become evident 

 from the observation of the xylose-broth tubes. 



These observations would seem to indicate that even in the 

 slowest xylose fermenters the xylose utilizing power is potentially 

 retained as a latent characteristic. This would prevent our 

 correctly applying to such cultures the term "mutation" in the 

 sense of de Vries. Working with bacteria we are enabled to 

 observe in a short time a sequence of generations far beyond 

 anything that can be observed with higher plants and our work 

 suggests, though of course in an entirely inconclusive way, that 

 at least some of the "mutations" described by botanists may 

 represent, in fact, a suppression of characteristics which remain 

 latent and might easily become apparent again could a sufficient 



