170 THE ANTIBIOTICS 



groups are active primarily against fungi, and not at all or to only a limited 

 extent against bacteria and actinomycetes. 



Groups 11 and 12 comprise the substances active primarily against proto- 

 zoa and viruses, respectively. Finally, another group could comprise those 

 substances (which we hope will be discovered) that are active primarily 

 against neoplastic tissues and not against healthy cells of higher forms of 

 life ; these substances may be more in the nature of antibiotic-like prepara- 

 tions than true antibiotics, unless they are found to be also active against 

 microorganisms. 



Specific antibiotic spectra, activity against test organisms made resistant 

 to known antibiotics, solubility properties, pigmentation, chemical nature, 

 and toxicity to animals are among the more important properties that help 

 to identify not only the groups but also the individual antibiotics within 

 or outside each of these groups. 



In preparing the keys for the identification of the actinomycetes, it was 

 not the aim of the authors to make necessarily a logical classification of the 

 antibiotics produced by actinomycetes, but to furnish workers in the field 

 with a tool enabling them to recognize the known antibiotics and thus to 

 facilitate establishment of any unknown agents. 



It is not the absolute aim of the keys to permit final identification of a 

 freshly isolated substance but, rather, to facilitate narrowing down the 

 number of closely related substances. The final identification of an "un- 

 known" antibiotic should be made only by running side to side such tests 

 as paper chromatograms, countercurrent distribution, chemical tests, anti- 

 microbial spectra, including use of resistant test organisms, and toxicity 

 tests comparing the "unknown" with standard preparations of known anti- 

 biotics. 



Interpretation of many of the criteria in these keys can vary from one 

 worker to the other and with the various strains of microorganisms used in 

 tests. Consequently, we have tried to list the same antibiotic in different 

 groups when we thought that it could be so classified. We have not been 

 able to cover all the possibilities and we urge the users of these keys to keep 

 in mind the fact that an antibiotic, like a biological system, is not charac- 

 terized by a single property but by a group of properties. 



Key I to the Identification of Antibiotics of Actinomycetes 



A. Substances active primarily against gram-positive bacteria. 



I. Soluble or slightly soluble in ether and in other organic solvents, 

 difficultly soluble in water. 



1. Red, red-orange, yellow, or violet pigmented substances. 

 a. Red to orange, very toxic. 



