30 INFECTION AND IMMUNITY, 



This relationship is investigated experimentally 

 either by growing two organisms in mixed cul- 

 tures,, noting subsequently whether one has out- 

 grown the other,, or one may be grown on a me- 

 dium which has previously been utilized by the 

 other. The predominance of one or the other may 

 depend on the nature of the culture medium. This 

 principle is utilized in obtaining pure cultures of 

 the cholera vibrio from dejecta by the use of a 

 strong alkaline medium which favors the growth 

 of the cholera vibrio but inhibits that of the other 

 intestinal bacteria. Similarly the diphtheria bacil- 

 lus grows well on Loeffler's blood serum, whereas 

 the other organisms commonly found in the throat 

 do not. 



Garre distinguished a one-sided and a mutual 

 antagonism between bacteria, but the former seems 

 to be the more common. Examples of favorable 

 symbiosis on suitable culture media are the fol- 

 lowing : Streptococcus and cholera vibrio ; anthrax 

 and pyocyaneus bacilli (Turro) ; diphtheria bacil- 

 lus and the streptococcus (Hilbert). In plate cul- 

 tures it has been found that the influenza bacillus 

 produces unusually large colonies when they lie 

 adjacent to colonies of the staphylococcus (Grass- 

 berger), and that it grows vigorously on agar 

 which contains killed bodies of the gonococcus or 

 diphtheria bacillus (Cantani). It has been noted 

 that the diphtheria bacillus is stimulated to a 

 greater production of toxin by the presence of 

 streptococci. 

 Mixed The coexistence of two or more micro-organisms 



Infections*. . , . -. -,... . /, 



in a morbid condition is 01 irequent occurrence, 

 and some of the most interesting and important 



