260 THE OUTLOOK FOR THE FUTURE 



lated from soil microorganisms that are active not only m 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 enriched soil specific antagonistic 

 organisms capable of destroying the pathogens, and finally isolating the 

 antibiotic substances from the bacteria. This work pointed to a new 

 method of approach to the isolation of antibiotic substances and attracted 

 the immediate attention of bacteriologists, chemists, and medical inves- 

 tigators. One no longer had to depend for the isolation of antagonistic 

 organisms upon mere air contaminations 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 destroying sfecific disease-producing bac- 

 teria. The mechanisms whereby such destruction was brought about 

 were found to be due to the production of characteristic substances, 

 known as antibiotic agents. The isolation of each required special meth- 

 ods, because of its specific chemical nature. Since most of the antibiotic 

 substances are selective in their action upon different 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 agents active upon gram- 

 positive bacteria as well as gram-negative forms. 



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

 poisons. 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 antibiotic substances act in 

 vivo against a variety of diseases, that branch of medical science known 

 as chemotherapy acquired a new group of tools. This work led to a re- 

 examination of the potentialities of penicillin, which in turn led to the 

 second important contribution, namely, the work of Chain and Florey 

 and their co-workers. These investigators succeeded in obtaining crude 

 active preparations of penicillin, which, they demonstrated, had a 

 marked effect upon various gram-positive bacteria In the animal body. 

 The importance of this discovery was accentuated by the great need of 

 the moment and the urgency for new methods of combating infections 

 resulting from World War II. These investigations immediately at- 



