OUTLOOK FOR THE FUTURE 315 



bound to enrich the subject of control of disease came only a little more 

 than half a decade ago. 



In 1939, Dubos announced that new antibacterial agents can be iso- 

 lated from soil microorganisms that are active not only in vitro but also 

 in vivo. He proceeded with the isolation of such substances in a novel 

 and unique manner, which consisted in enriching the soil with patho- 

 genic bacteria, isolating from such soil specific antagonistic organisms 

 capable of destroying the pathogens, and finally producing the specific 

 antibacterial substance by cultivating the organism on suitable media. 

 This work pointed to a new method of approach to the isolation of anti- 

 biotic substances and attracted the immediate attention of bacteriolo- 

 gists, chemists, and medical investigators. One no longer had to depend 

 for the isolation of antagonistic organisms upon mere air contamina- 

 tions of exposed bacterial plates, or upon accidental observations of the 

 destructive action of one microbe upon another. One could now proceed 

 systematically with the isolation of microorganisms capable of destroy- 

 ing sfecijic disease-producing bacteria. The mechanisms whereby such 

 destruction was brought about were found to be due to the production 

 of characteristic substances, known as antibiotics. The isolation of each 

 antibiotic required special methods, because of its specific chemical na- 

 ture. Since most of the antibiotics are selective in their action upon dif- 

 ferent bacteria, affecting some and not others, the method proved to be 

 of great importance in pointing a way to the isolation of a variety of 

 chemical agents active upon gram-positive bacteria as well as gram- 

 negative forms. 



It was not sufficient, however, merely to isolate these protoplasmic 

 poisons from the cultures of the antagonistic microorganisms. It was 

 essential to determine the effect of animal tissues upon the action of 

 these agents and to establish their selective activity upon the bacteria in 

 the animal body as compared to the test tube. However, once it was 

 recognized that some of these antibiotics act in vivo against a variety of 

 diseases, the branch of medical science known as chemotherapy acquired 

 a new group of tools. This work led to a reexamination of the potentiali- 

 ties of penicillin, which in turn led to the second important contribution, 

 namely, the work of Chain and Florey and their co-workers. These in- 



