170 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



analyzes: 59.4 per cent C, 6.8 per cent H, 13.5 per cent N, 2.7 per cent 

 CI. The molecular weight Is about 1,260 or a multiple of this number. 

 Tyrocidine is a salt of a polypeptide having free basic amino groups. 

 The <^-amino acids make up 20 per cent of its a-amino groups. The most 

 probable molecule was shown to contain two amino groups, three amide 

 groups, and one weakly acidic carboxyl or phenolic group, with a molec- 

 ular weight of 2,534. Among the amino acids, tryptophane, tyrosine, 

 and dicarboxylic-amino acids, including aspartic acid, have been de- 

 tected (126, 434). 



The tyrothricin type of antibiotic substance appears to be widely dis- 

 tributed among spore-forming aerobic soil bacteria (427, 428, 857). 

 The following method for its extraction has also been employed: A 

 seven-day-old bacterial culture was treated with 2 to 5 per cent of an 

 electrolyte and HCl added to give a ^H of 4.0. A precipitate was 

 formed which was centrifuged and extracted with 95 per cent alcohol, 

 until no more turbidity could be observed after dilution with an equal 

 volume of water. The alcoholic extracts were evaporated to dryness and 

 extracted with ether, petroleum ether, and benzol, in which the active 

 substances are insoluble. The residue was then dissolved in absolute 

 alcohol, and the concentrated solution dialyzed for 24 hours against 

 running tap-water and for 24 hours against distilled water. The active 

 substance was obtained partly in a precipitated form and partly in a 

 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 (427a, 885). 



A thermostable substance was obtained (149) from B. simplex, an 

 organism capable of bringing about the destruction of various patho- 

 genic fungi. It was produced by the bacterium grown both on synthetic 

 and organic media. It can be adsorbed on activated charcoal and recov- 

 ered from the latter by the use of hot alcohol. 



To what extent substances of bacterial origin that are toxic to brain 

 tissues, like toxoflavin (C6H6N4O2), are also effective against bacteria 



