SUBSTANCES PRODUCED BY BACTERIA 183 



has little effect upon the gram-negative bacteria, except the meningo- 

 cocci. Among the fungi, only Blastomyces dermatiditis is susceptible. 

 The action of the pigment is greatly affected by serum (569). 



It may be added here that certain aromatic oils and various fatty acids 

 possess marked bactericidal properties (518). Unsaturated acids are 

 more active than saturated acids (1040). Ordinary peptones have also 

 been found to contain a substance that is active against various bacteria, 

 especially when small amounts of inoculum are used (202). The active 

 substance is thermostable and is associated with an acid-precipitated 

 fraction that is pigmented and changes color upon oxidation and reduc- 

 tion. The bacteriostatic effect of this material can be corrected by the 

 addition of reducing agents, such as thioglycollic acid. The bacterio- 

 static action of dyes is well known and need hardly be discussed here. It 

 is sufficient to mention, for example, methylene blue and indophenols 

 in oxidized forms. 



Pyo-compounds. Doisy and his collaborators (389) centered their 

 attention upon the antibiotics present in the Ps. aeruginosa cells. This 

 group of compounds was designated as Pyo I, Pyo II, Pyo III, and Pyo 

 IV. The culture of the organism was incubated for 5 weeks, cooled, and 

 acidified with HCl to ^H 't^.S'-, it was centrifuged, and the precipitate 

 was extracted with hot 95 per cent ethyl alcohol. The alcohol extract 

 was diluted with water to 80 per cent alcohol and treated with petro- 

 leum ether, to remove the fats and fatty acids. The alcoholic solution 

 was evaporated and the aqueous residue extracted with ether. The ex- 

 tract was separated into the four fractions listed above, which repre- 

 sented pure, crystalline, active substances. These fractions were struc- 

 turally related and were more active against the gram-positive than the 

 gram-negative bacteria. They were nontoxic to animals. 



Polysaccharidases 



Among the antibiotic substances of microbial origin may also be in- 

 cluded the enzyme systems that have the capacity of decomposing the 

 capsular substance of certain bacteria, thereby rendering them more 

 readily subject to destruction in the blood stream or in other substrates. 

 The first enzyme of this type was isolated by Dubos and Avery (204, 



