254 NATURE OF ANTIBIOTIC ACTION 



Gramicidin and tyrocidine were believed to affect bacteria by depress- 

 ing the surface tension of aqueous solutions. This effect was favored by 

 the addition of organic solvents such as glycerin, which increases the 

 solubility of gramicidin. The addition of serum resulted in a decrease in 

 activity of tyrocidine, to a less extent, however, than of gramicidin. 

 Heat destroyed the bacterial and hemolytic effects of gramicidin, but 

 the property of altering surface tension was heat-stable. It has further 

 been shown (405) that gramicidin, after an initial stimulation, inhibited 

 oxygen consumption of bovine spermatozoa and rendered them im- 

 mobile ; aerobic as well as anaerobic glycolysis was depressed by about 

 40 per cent and motility of the spermatozoa impaired. Tyrocidine, 

 however, caused a small reduction in the oxygen consumption and in 

 glycolysis. The action of gramicidin upon the metabolic activities of S. 

 aureus and S. hemolyticus was shown (210) to be influenced by the 

 composition of the medium, the presence of potassium and phosphate 

 ions giving a prolonged stimulation of metabolism, whereas ammo- 

 nium ions favored a depression in oxygen uptake. 



The specific effects of basic proteins, such as protamine and histone, 

 upon the activity of selective inhibitors offered a possible explanation 

 for the difference in the action of tyrothricin upon gram-positive and 

 gram-negative bacteria ( 645 ) . These basic proteins also possess antibac- 

 terial properties. They have the capacity of sensitizing gram-negative 

 bacteria by means of substances which otherwise act only on gram- 

 positive forms. 



Pneumococci grown in media containing the specific enzymes which 

 hydrolyze their capsular material are deprived of these capsules and 

 fail to agglutinate in the specific antiserum. The enzymes do not inter- 

 fere with the metabolic functions of the cells, but their action is directed 

 essentially against the capsule. These enzymes were found not only to 

 exhibit great selectivity but to be highly specific against the particular 

 polysaccharides. 



The respiratory enzymes of bacteria, such as S. aureus, that are sensi- 

 tive to citrinin were found (643) to be inhibited by this antibiotic, but 

 not the corresponding enzymes of resistant bacteria, such as E. coU. 



The possible interference of penicillin with the metabolism of bac- 

 teria has attracted considerable attention due to the great practical im- 



