104 ATLAS OF BACTERIOLOGY. 



9. EFFECT OF OTHER BACTERIA UPON BACTERIAL 

 GROWTH. 



Although it is the object of every bacteriologist to 

 obtain only pure cultures, it must not be forgotten 

 that in nature bacteria often appear in mixed cul- 

 tures. When water, milk, the intestinal contents of 

 sick or healthy individuals, etc., are examined, sev- 

 eral varieties will always be found at the same time. 

 Although this admixture usually appears to 'be 

 purely accidental, it is found on closer investigation 

 that, in the domain of bacteriology, there are syn- 

 ergetic (favoring the growth of one another) and 

 antagonistic (injuring one another) varieties. Nencki 

 speaks of symbiosis and enantobiosis. 



Garre demonstrated the antagonism experimentally 

 by making streak cultures of various bacteria upon 

 gelatin plates, in the shape of parallel or intersect- 

 ing lines. It was then found that certain varieties 

 thrive very poorly or not at all when another variety 

 is growing in their immediate neighborhood. In 

 very many cases the antagonism is one-sided. For 

 example, bacterium putidum grows very well when 

 inoculated between closely approximated, well-devel- 

 oped streaks of staphylococci. On the other hand, 

 micrococcus pyogenes does not grow when inoculated 

 between luxuriantly developing cultures of bacterium 

 putidum, and the former remains very meagre when 

 both varieties are applied in streak cultures at the same 

 time (Garre: Corresp. f. Schweizer Aerzte, 1887). 



Or we make plates of gelatin or agar (for liquefy- 

 ing varieties) which have been infected, in the melted 



