CH. v] VARIATIONS IN FERMENTING POWER 59 



Burton Bradley (1910) repeated these experiments with 

 success as regards dulcitol and arabinose. 



Penfold states that in the case of B. typhosus the acquire- 

 ment of new fermenting properties on the part of certain 

 individuals of the strain is indicated, in some instances, by 

 the formation of papillae on the colonies. He observed this 

 to take place in a medium containing dulcite or sorbite. In 

 his opinion considerable permanency in the new fermenting 

 power was indicated if the papillae formation arose early and 

 without subculture. 



IX. Variation in fermenting power may be brought 

 about by a process of Artificial Selection. 



Goodman (1908) made a series of cultures of B. diph- 

 theriae in dextrose broth. From this series he selected the 

 tube giving the greatest acidity, when titrated against a 

 standardised soda solution, and the tube giving the lowest 

 acidity. From each of these two tubes he made a fresh series 

 of cultures and, after 3 days' growth at 37 C., he chose out of 

 the more acid series the tube giving the greatest acidity, and 

 out of the less acid series the tube giving the lowest acidity. 

 With these two tubes he made a fresh double series of 

 cultures and repeated the process of selection. After repeating 

 this 36 times he obtained one culture which produced intense 

 acidity in dextrose, and a second culture which failed to pro- 

 duce acidity in dextrose at all and in fact made it more 

 alkaline. These two strains were then tested with other 

 sugars and it was found that, in both cases, the power to 

 ferment maltose was diminished while the power to ferment 

 saccharose was increased. Their action on dextrin was not 

 affected. 



It is to be noted that the difference in fermenting power 

 between these two selected strains was as great as that 

 normally existing between B. diphtheriae -and B. pseudo- 

 diphtheriae. 



This process of continued selection in opposite directions 

 does not necessarily succeed in developing strains of extreme 

 type. For example, Buchanan and Traux (quoted by Rettger 



