THE VITAL CONDITIONS OF BACTERIA. 105 



condition, with an equal number of individuals of two 

 different varieties of bacteria. In many cases only 

 one variety will undergo development (Lewek: C. B., 

 VII., 107). 



The following is the third method of making the 

 experiment. The same fluid nutrient medium is in- 

 oculated with two varieties and later we ascertain the 

 victor in the struggle, either with the microscope or 

 macroscopically upon thin plates. To this category 

 belongs the frequent experience that fermentation- 

 producers, when present in large numbers in a suit- 

 able medium, prevail over contaminating bacteria. 

 The latter sometimes disappear entirely. 



The following practical inference may be drawn 

 from these experiences. In counting bacteria very 

 dense plates may not be regarded as decisive, and in 

 the isolation of certain varieties thin plates may also 

 be necessary. For example, in isolating bacterium 

 Pfliigeri from an abundance of bacterium putidum; 

 no bacteria Pfliigeri grow within a circle of several 

 millimetres around each culture of bacterium putidum 

 (K. B. Lehmann). 



Finally, bacteria may antagonize one another with- 

 in the animal body. As Emmerich showed, animals 

 infected with anthrax may be saved by subsequent 

 inoculation with streptococcus pyogenes. It is im- 

 possible to enter into the mechanism of this process 

 within the limits of this work. 



Greater practical importance attaches to the sym- 

 biosis of bacteria, as is shown by the following 

 examples. 



1. A series ol bacteria thrive better in company 

 with others than alone. Certain anaerobics even 



