260 NATURE OF ANTIBIOTIC ACTION 



the substance was found to behave as the mirror image of tellurite in 

 inhibiting specific bacteria. Penicillin was also utilized for the separation 

 of acne bacilli from accompanying staphylococci (158) and for the 

 separation of streptococci from staphylococci (262) j also for the isola- 

 tion of Trichomonas vaginalis and of animal viruses (803). 



Actinomycin was used to separate gram-negative from gram-positive 

 bacteria (974). 



Tyrothricin has been utilized (886) for the isolation of A^. gonor- 

 rhoeae from contamination with gram-positive bacteria. Usually a 

 1 : 15,000 dilution of the substance in "chocolate" agar was found quite 

 satisfactory for this purpose. By the use of tyrothricin, gram-negative 

 microorganisms have been isolated from the nasopharynx even in the 

 presence of overgrowth by gram-positive cocci. Hemophilus influenzae 

 is resistant to the action of tyrothricin, and its isolation is facilitated by 

 adding to the media on which it is cultured tyrothricin in a dilution 

 which inhibits the cocci (842). 



Streptothricin was found to help in distinguishing B. tnycoides from 

 B.subtilis (979). 



SUMMARY 



Comparatively little is yet known of the mode of action of antibiotic 

 substances. This field offers great opportunities for research and utiliza- 

 tion of bacterial activities. The solution to such important problems as 

 the morphology of the bacterial cell} taxonomic relations of bacteria j 

 various physiological reactions of microorganisms, especially the phe- 

 nomenon of adaptation of bacteria to antibiotics and the problem of 

 bacterial resistance} the mechanism of causation of disease; and the 

 very control of disease-producing microorganisms — all fundamental 

 problems in microbiology — will be furthered by knowledge of the ac- 

 tion of specific antibiotic substances upon bacteria and other micro- 

 organisms. 



