Effects of Bacterial Growth on the Environment 193 



than the number of Hves lost during all the wars throughout man's 

 histoiy. 



Since penicillin is rather selective in its reaction, organisms 

 found to be resistant to this substance had to await the discovery of 

 additional antibiotics. The search continues today for new and 

 more powerful agents. Unfortunately, with the passage of time, 



Fig. 33. Bacitracin assay plate showing inhibition zones against 

 Micrococcus fiaviis. (Courtesy of Commercial Solvents Corporation, 

 New York, New York.) 



medical men have discovered that many bacteria formerly sensitive 

 to the action of particular antibiotics have built up a tolerance 

 which limits the agents it is possible to employ against these infec- 

 tions. Whereas penicillin came about as an accidental discovery, 

 the dozens of antimicrobial agents developed since then have been 

 the result of highly organized searches for new weapons in the 

 antibiotic arsenal. Many organisms produce antibiotics that are 



