VIII. B, 6 Barber: Dysentery Bacilli 543 



types was tested by selecting individuals at random from each 

 type and testing the characteristics of their offspring. 



From a culture of the red, or maltose-fermenting, series, 10 

 single cells were isolated and their offspring tested on maltose 

 agar. All gave the characteristics of the red variety. From 

 another one of the original 5 red cultures, 12 isolations gave 

 red cultures on maltose agar. After an interval of four days, 

 13 new isolations were made from one of the 12, selecting a tube 

 which gave a deeper red than the average. All gave red cultures. 

 A subculture of one of these 13 showed a tendency to blue, and 

 some days later 24 new isolations were made from it, and at the 

 same time 26 isolations were made from one of the same lot 

 which showed a deeper red than the average. All 50 of these 

 gave cultures which were alike red. Apparently selection in 

 the direction of red or blue in this red series showed no progres- 

 sion toward either color, and it is probable that the slight varia- 

 tions in color were due to some inequalities in the medium. 



From one of the original 16 blue, 11 cells were selected, all 

 giving cultures of the blue type. From another one of the orig- 

 inal 16, 16 single cells were isolated and gave blue cultures, 

 and from one of this second group 23 isolations were made and 

 all gave a similar blue type. All blue cultures gave secondary 

 colonies fermenting maltose. No red cultures showed such 

 colonies. The selections are given graphically in the chart 

 below : 



Original culture. 



I 

 21 



I 



I" ^ I 



5 red 16 blue 



10 red 12 red 11 blue 16 blue 



I I 



13 red 23 blue 



24Jred 26 red 



During the period of these isolations the stock cultures were 

 kept on maltose agar except shortly before isolations, when 

 they were transferred to ordinary broth to obtain actively grow- 

 ing cells for isolation. In obtaining material for selection from 

 the blue type, transfers were made from growths between sec- 



