160 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



tion. Differences between various compounds may often be in degree 

 rather than in kind. Different organisms may produce the same kind of 

 compound. Many organisms are able to produce more than one anti- 

 biotic substance: B. hrev'ts produces tyrocidine and gramicidin j P. no- 

 tatum forms penicillin and notatinj 5. antibiot'icus produces actino- 

 mycin A and Bj ^4. fumigatus forms fumigatin, fumigacin, spinulosin, 

 and gliotoxinj A. flavus produces aspergillic acid and flavicin. 



On the basis of their solubility, the antibiotic substances may be di- 

 vided into three groups : 



Group A. Soluble in water at different reactions, and insoluble in ether. 

 These substances usually represent polypeptides, proteins, organic 

 bases, or adsorption compounds on protein molecules. Most of them 

 have not been isolated in a pure state. They comprise the bacterial 

 enzymes acting upon microbial polysaccharides, actinomycetin, mi- 

 crobial lysozyme, streptothricin, streptomycin, notatin, and pyo- 

 cyanin. 



Group B. Soluble in ether and in water at proper reactions. Here belong 

 some of the most important antibiotic substances so far isolated and 

 described, namely, penicillin, flavicin, citrinin, clavacin, proactino- 

 mycin, penicillic acid, and aspergillic acid. 



Group C. Insoluble in ether and in water. These include gramicidin, ty- 

 rocidine, subtilin, and the B. simflex factor. 



Group D. Soluble in ether and insoluble in water. Here belong fumi- 

 gacin, fumigatin, gliotoxin, actinomycin, pyocyanase, and others. 



Some of the antibiotic substances have been crystallized, and infor- 

 mation has been gained concerning the approximate chemical nature of 

 others j many others are still imperfectly known. On the basis of their 

 chemical nature, the antibiotic substances may be divided as follows: 



Lipoids and lipoid-like bodies, including pyocyanase and certain little 

 known microbial extracts 



Pigments, namely, pyocyanin, hemipyocyanin, prodigiosin, fumigatin, 

 chlororaphin, toxoflavin, and actinomycin 



Polypeptides, comprising gramicidin, tyrocidine, subtilin, and actino- 

 mycetin 



Sulfur-bearing compounds, such as gliotoxin and chaetomin 



