SUBSTANCES PRODUCED BY BACTERIA 165 



acidified and treated with petrol ether, which brought the active sub- 

 stance into solution. The active substance was again dissolved in alcohol 

 and taken up in ether. The ether solution was washed with water, evapo- 

 rated, and dried. One liter of a 30-day-old culture of B. mesentericus 

 gave 1 62 mg. of petrol-ether-soluble fatty acids and an oily substance 

 of a brownish color. It was neutralized with NaOH solution and tested. 

 The extract diluted to 1:7,500 killed diphtheria j a 1:1,000 dilution 

 was required to kill staphylococci. Iso-valerianic acid and oleic acid, 

 isolated from this material, had a similar bactericidal action. Weaken- 

 ing of the substance by heating was demonstrated and was believed to 

 be due to a break in the double bond of the oleic acid. 



E. colt exerts an antagonistic effect in vivo when injected subcutane- 

 ously or when used for feeding. It produces (365, 367) a thermolabile 

 substance that was considered to be a lipoid in character. According to 

 Hettche (408, 409), one is dealing, in the case of bactericidal constitu- 

 ents of the bacterial cell, with lipoids that contain unsaturated fatty 

 acids. 



Chromobacterium iodinum produces {SSSi SS^) ^ purple-bronze pig- 

 ment designated as iodinin and found to be a di-N-oxide of dihy- 

 droxyphenzine. This substance inhibits the growth of streptococci (S. 

 hemolyticus) in concentrations of 1.2 to 2.0 x io"° M. 



It may be added here that certain aromatic oils possess marked bac- 

 tericidal properties. Ordinary peptones have also been found to contain 

 a bacteriostatic substance that is active against various bacteria, especially 

 when small amounts of inoculum are used (191). The active substance 

 is thermostable and is associated with an acid-precipitated fraction that 

 is pigmented and changes color upon oxidation and reduction. The bac- 

 teriostatic effect of this material can be corrected by the addition of re- 

 ducing agents, such as thioglycollic acid. The bacteriostatic 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 (197). 



PoLYSACCHARiDASES. Among the antibiotic substances of microbial 

 origin may also be included the enzyme systems that have the capacity 

 of decomposing the capsular substance of certain bacteria, thereby ren- 

 dering them more readily subject to destruction in the blood stream or 



