ANTIBIOTICS AS CHEMOTHERAPEUTIC AGENTS 287 



tissue after an exposure period of lO minutes at 37° C. to the highest 

 dilution that kills S. aureus under the same conditions. A unit of sub- 

 tilin has been defined as that amount present in i ml. of the highest di- 

 lution (expressed in mg.) capable of killing S. aureus in 10 minutes at 

 37° C. 



It is relatively nontoxic when tested by the tissue culture method j it 

 is about 20 times more toxic to S. aureus than to chick heart tissue. It 

 exerted a suppressive effect upon experimental tuberculosis in guinea 

 pigs, and protected animals against infection with pneumococcus Type 

 III and B. anthracis. 



Bacitracin appears to have chemotherapeutic potentialities. 



Pyocyaneus Prefarations 



Although, as pointed out previously, pyocyanase, the first antibiotic 

 to be isolated, came into disrepute as a potential chemotherapeutic 

 agent, various preparations of Ps. aeruginosa have continued to receive 

 attention. One must differentiate among the lipoidal products and 

 other antibiotics isolated either from the culture medium or from the 

 bacterial cells of this organism (50a). The lipoid products obtained by 

 chloroform extract of bacterial cells were found to be active against 

 various gram-positive bacteria including M. tuberculosis in concentra- 

 tions of 1:500 (15 minutes) to 1:500,000 (5 hours) j it was effective 

 not only in vitro but also in vivo, a-oxy-phenazine obtained in a crystal- 

 line state was active against various gram-positive and gram-negative 

 bacteria. It was effective against bovine mastitis and Br. abortus in 

 guinea pigs (1053). 



Streftothricin and Streftomycin 



Among the antibiotic substances that are active against gram-negative 

 bacteria both in vitro and in vivo, streptothricin and streptomycin oc- 

 cupy a prominent place. Their toxicity is low enough to make possible 

 the administration of doses sufficient to destroy the pathogens in the liv- 

 ing tissues (792, 794). In the very first experiments, using chicken egg 

 embryos, mice, and other experimental animals, they gave favorable 

 results in the treatment of Br. abortus, bacillary dysentery, typhoid 

 fever, and food poisoning produced by Salmonella organisms and 



