188 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



colloidal solution in the dialysis bag. Upon evaporation of the water, a 

 highly active, grayish-white powder was obtained. One hundred liters 

 of medium gave 15 grams of purified active substance. The activity 

 could be tested by inhibition of encapsulation of Friedlander's bac- 

 terium j this was brought about by the addition of 4 mg. to i ml. of cul- 

 ture medium. This preparation was later found to be identical with 

 gramicidin (443,911). 



Gramicidin S (43, 324) is related to the tyrothricin complex, being 

 tyrocidine in nature. It was found (894) to be a cyclopeptide, with a 

 stoiochiometric minimum unit formed from one residue each of /-orni- 

 thine, /-proline, /-valine, /-leucine, and ^-phenylalanine. The unit pos- 

 sesses one free amino group, no free carboxyl groups, and one residue 

 of chloride. 



Bacitracin is formed by certain strains of B. subtilis grown in shallow 

 layers of media. A heavy surface pellicle is produced after 3 to 5 days' 

 incubation at 37° C. The medium is extracted with normal butanol and 

 concentrated by steam distillation in vacuo, giving a grayish-white 

 powder. The substance is neutral and water soluble and withstands heat- 

 ing for 15 minutes at 100° C. without significant loss of activity. It is 

 stable in acid solution but unstable in alkaline solution above fH 9, and 

 is not digested by proteolytic enzymes. It is active chiefly against gram- 

 positive organisms, but the gonococcus and meningococcus are also 

 susceptible to it. It is active in vivo against experimentally produced 

 hemolytic streptococcus and gas gangrene infections (469). 



Subtilin is produced by certain strains of B. subtilis. It is a polypep- 

 tide and is readily digested by proteolytic enzymes. It is most active at 

 /»H 2.2 and gradually becomes inactivated with decreasing acidity. It 

 is active against various gram-positive bacteria, acid-fast bacteria, and 

 certain pathogenic fungi (816). Eumycin, produced by certain strains 

 of B. subtilis and active largely against fungi, actinomycetes, and myco- 

 bacteria, although showing little effect against staphylococci may also 

 belong to this group (471). Subtilysin was reported to have a lytic ac- 

 tion against gram-negative bacteria, none against cocci (925). Some of 

 the subtilin preparations also have the capacity of inactivating bacterial 

 toxins, such as diphtheria, tetanus, and others. This property was as- 



