VIII. B, 6 Barber: Dysentery Bacilli 545 



the second, and 1 in 123 in the third — the proportion becoming 

 smaller as the months went on. In addition, there occurred 

 varieties v^ith less power of fermenting maltose, but otherwise 

 corresponding tcr the acid type. 



As a further test of the constancy of an acid-forming strain, 

 single cells were isolated from a red strain which had been 

 cultivated two months on ordinary agar at room temperature. 

 It had been passed through 5 subcultures, and neither it nor the 

 culture from which it was isolated had been grown on maltose 

 agar. Twenty-nine such isolations gave cultures all of which 

 completely fermented maltose-litmus agar. 



In order to test the behavior of the red and blue varieties 

 in ordinary broth alone and in competition with each other, 

 the following experiment was arranged: 



Into 4 tubes of ordinary broth, A, B, C, and D, equal amounts 

 were sown of the red and blue strains. In order to have exactly 

 equal sowings of the two varieties, the following method was 

 followed : Single cells of each of the two types were isolated 

 and grown from one to two hours in hanging drops until 3 

 generations had formed, that is, until 8 new individuals had 

 formed from one. Then to a tube of ordinary broth 8 bacilli 

 of the red and 8 of the blue strains were added, selecting such 

 hanging drops as showed elements of approximately equal size. 

 This was done in 4 tubes and the fifth, E, was given 5 bacilli 

 of the blue and 6 of the red variety. For comparison, a tube 

 was sown with a pure culture of the red and one with a pure 

 culture of the blue type. These tubes were incubated one day, 

 then transfers made by platinum loop to fresh broth and at 

 the same time to maltose agar, in order to observe any fer- 

 mentative changes. This was continued through 10 daily 

 transfers. 



At the end of the series, the red control remained red as 

 before, and the blue distinctly blue with secondary colonies; 

 while of the 4 which received mixed sowing in equal quantities, 



1, A, was blue with secondary colonies like the blue control, 



2, B and C, showed mixed red and blue, while the fourth, the 

 one which had received a slightly larger amount of red strain, 

 was as red as the red control. In order to test the composition 

 of the cultures, a new transfer was made at the end of the series 

 to ordinary broth to obtain freshly growing cells, and 19 single 

 cells were isolated from A of the mixed series, a culture which 

 showed all blue. All 19 gave typical blue colonies. Ten similar 

 isolations from D, which showed a mixed coloration on maltose 

 agar, gave 8 of the red and 2 of the blue ; 12 isolations from the 



