BIOLOGICAL VARIATIONS OF BACTERIA 387 



and incubated for three or four days, at which time 1 cc. of 7.5 

 per cent of phenol was added to the culture. The phenol ex- 

 posure was limited to two to three minutes at the beginning of 

 the experiment and then the time was gradually ncreased with 

 each transfer until thirty or more minutes time was attained. 

 The exposed culture was then reinoculated into plain broth 

 by i:ouring over a small quantity (0.5 to 1 cc.) from it. Con- 

 tinuous growth of the B. coli in 0.75 per cent of phenol broth 

 was also tried, beginning with 0.25 per cent, with the same gen- 

 eral results. The transplanting in all media was carried out 

 every three or four days over periods varying from one to three 

 months, thus allowing from ten to thirty transfers. The ex- 

 periments were repeated two or three times to assure constant 

 and uniform findings. 



Control cultures were carried on in plain broth throughout 

 the experiment. It might be stated at once that there were 

 very sHght variations between the original stocks and these 

 control cultures, no more than would be expected as normal 

 variations. These were seen as slightly increased or decreased 

 amounts of gas or acid formation, differences in time of coagula- 

 tion, or slight changes in the growth on potato. At no time, 

 however, were the biological characteristics markedly changed 

 nor enzyme production completely inhibited simply by continual 

 passage through broth. 



The accompanying tables show the results obtained in some 

 of the more typical series of experiments. These tabulations 

 were all made at seventy-two or ninety-six hours after inocula- 

 tion and were verified again, especially those on potato and in 

 milk, after a week or ten days growth. The tests for indol were 

 made as described below after seven days growth. 



