THE MICROBIOTTCS — McDONNELL 445 



IDENTIFICATION 



In 1932 other British workers, Clutterbuck, Lovall, and Raistrick, 

 verified Fleming's experimental reports and with the cooperation of 

 the noted American mycologist Thorn, correctly identified the mold 

 as P. notatum Westling. Fleming continued his studies but contented 

 himself with reporting that it did not disturb human white blood cells, 

 and that it appeared to have some value for local treatment of derma- 

 tologic infections. He employed the filtrate chiefly to inhibit con- 

 taminants in the isolation of organisms insensitive to penicillin, such 

 as Hemophilus influenzae. 



Clutterbuck in 1932 attempted to isolate the active principle from 

 the penicillin filtrate but failed, and with Fleming's reluctant agree- 

 ment concluded that the substance was too labile. Thus, except for 

 occasional use as a differential culture, Fleming's discovery lay dor- 

 mant for 10 years. 



LYSOSYME 



In 1929, the year of Fleming's first report, another British investiga- 

 tor, Howard Florey, and his associates at Oxford began work on lyso- 

 syme, an antibiotic substance discovered 7 years before by Fleming, 

 and ultimately crystallized in 1937 by Roberts. During the next dec- 

 ade Florey continued his progress, firmly convinced that somehow an 

 antibiotic would be discovered that would be nontoxic to man yet of 

 value in the treatment of infections. The mechanism of these sub- 

 stances was not clearly indicated, but the principle upon which they 

 acted was generally accepted. Florey studied many organisms but to 

 no avail until 1938 when he directed his attentions to penicillin. 



SOIL BACTERIA 



During this period, other equally striking work had been conducted 

 in the United States. In the course of studies at the Rockefeller 

 Institute for Medical Research in New York on the virulence of dif- 

 ferent types of pneumococci, Dubos in 1938 completed a successful 

 search for a specific bacterial enzyme which by decomposing the 

 capsular polysaccharides of the organisms would render the pneu- 

 mococci avirulent. He believed that micro-organisms existed which 

 would attack other unrelated microbial cells, assuming that all organic 

 matter added to the soil eventually is decomposed by soil micro- 

 organisms. Dubos hoped that living cultures added to soil would 

 develop selective flora capable of attacking certain bacterial species. 

 He was successful in isolating such a material, and prepared from it 

 three active substances inhibitory to gram-positive organisms. They 

 were tyrocidine, gramicidin and gramidinic acid. 



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