4 



used. These streaks were plated out and from the colonies on the 

 plates new agar streaks were made and dextrose broth tubes inoculated 

 from these as before. In no case either in the plate or on the agar 

 slant was the culture allowed to come in contact with sugar until in- 

 oculated into broth. 



In the third series of cultures, the cultures were plated out as in 

 the other series, but the colonies were transferred direct to broth tubes 

 containing 1% of dextrose. The acidity was determined as before, but 

 in this series the culture in the tubes producing the highest and the 

 lowest amount of acidity were inoculated direct into sugar broth without 

 plating out, except to determine the purity of the cultures. 



In the tables are given the averages of the acid produced in the 

 high and low series. In most cases, the organism selected in the high 

 series produced a higher percentage of acid than the average, and the 

 organism selected in the low series produced a lower percentage of 

 acidity than is shown by the average of the series, but any true variation 

 should be transferred to all of the descendants, so that the average per- 

 centage of acid produced represents a fairly good index of the variation 

 of the acid producing power of the organism. From these tables, it is 



Proteus vulgaris 1. 



