163 



taining the same kind of medium. After sterilization in the autoclav, 

 the sac and flask are inoculated with the different cultures to be studied. 

 The sac prevents the bacteria from mingling but, being permeable, permits 

 the diffusible products of metabolism to distribute themselves uniformly 

 throughout the liquid medium. By taking samples from both tube and 

 flask and plating, it becomes a rather simple matter to determine whether 

 the life or the growth of either organism is affected by the manufactured 

 products or wastes of the other. 



The experiments were run in series. Each series consisted of five 

 flasks. Four of these contained B. typhosus in the sac and one of the 

 cultures of B. fluorescens in the flask. The fifth was used as a control and 

 contained only B. typhosus. Four of these series were run simultaneously. 

 The temperature was 37 degrees Centigrade. The experiments ran through 

 a period of twelve weeks. 



Of the strains of B. fluorescens used, cultures No. 29 and No. 469 im- 

 parted a very deep color to the medium after growing for twenty-four 

 hours ; No. 31 and No. 502 imparted very little color. 



The next table shows a certain correlation between the elimination 

 of B. typhosus by B. fluorescens cultures secreting a deep colored pigment 

 as compared with those cultures secreting very little pigment. 



Table II. 



After twenty-four hours incubation. 

 Flask-containing B. fluorescens. Sac containing B. typhosus. 



No. 29 Growth. 



No. 469 Growth. 



No. 502 Growth. 



No. 31 Growth. 



After forty-eight hours incubation. 

 No. 29 No growth. 



No. 469 No growth. 



No. 502 Growth. 



No. 31 Growth. 



After seventy-two hours incubation. 

 No. 29 No growth. 



No. 469 No growth. 



No. 502 Growth. 



No. 31 Growth. 



