222 DISEASE CONTROL 



have been reported (280). The pressed extract of Ps. aeruginosa had a 

 similar effect when injected in the animal simultaneously with the 

 pathogen (505). 



Various methods of treating severe infections, like anthrax (97) or 

 malignant tumors (138), with mild infective agents have been sug- 

 gested. The reduction in pathogenicity of one organism by the presence 

 of others has thus been well recognized (62, 120, 239). Nonpatho- 

 genic organisms apparently have specific effects upon the pathogens, the 

 development of which was prevented or even suppressed. The very oc- 

 currence of specific types of pneumococci in healthy individuals and the 

 causation of specific forms of pneumonia were found to be controlled 

 by the antagonistic effects of other microorganisms (369). 



It was thus definitely established that the growth of B. anthrads 

 could be inhibited by antagonists (48). Guinea pigs survived large in- 

 jections of washings from soil previously contaminated by B. anthrads 

 through the slaughtering of a diseased cow. When cultures of this or- 

 ganism were isolated from the soil and injected, however, characteristic 

 disease symptoms resulted. It was suggested that the anthrax spores are 

 digested by the leukocytes which have been attracted to the site of in- 

 jection by the accompanying bacteria (31). 



Seitz (812), in discussing the problem of mixed infections, cited 

 many cases not only of decreased but also of increased virulence of the 

 pathogen as a result of accompanying bacteria. He warned, therefore, 

 against too sweeping generalizations concerning the healing effect of 

 antagonistic bacteria. He believed that in many cases of artificial infec- 

 tion, the favorable action of the antagonist may have been due entirely 

 to increased body resistance. Nevertheless, he accepted the possibility 

 of utilizing the antagonistic effects of microorganisms, provided it did 

 not concern tissue or blood infection, but only skin surfaces, including 

 those of the intestinal canal and the vagina. 



Until very recent years, attempts to utilize the activities of antagonis- 

 tic microorganisms for the control of disease did not always meet with 

 success. This failure may have been due to an insufficient understanding 

 of the nature of the chemical agent produced by the antagonizing or- 

 ganism, to a lack of knowledge concerning the mechanism of its action. 



