216 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



lysozyme also was found (641 ) to produce an autolytic enzyme similar 

 to it. It has been suggested that the antibacterial action of saliva may 

 be due to the presence in it of antagonistic bacteria. The lysozyme of 

 saliva is known to act primarily upon gram-positive bacteria. A large 

 number of bacteria were tested (31) for their ability to antagonize 

 diphtheria and pseudo-diphtheria organisms. Only the spore-forming 

 B. mesentertcus and B. suhtills groups produced antagonistic substances, 

 but these bacteria were not found in the saliva. Cultures of bacteria 

 isolated from the saliva had no antagonistic effect, thus proving that the 

 action of saliva need not be due to its bacterial content. 



Milk 



Milk was found (694) to contain several thermolabile bactericidal 

 substances and two thermostable compounds which acted injuriously 

 upon lactic acid bacteria. Orla-Jensen emphasized that the growth of 

 bacteria in milk is influenced by a combination of activators or growth- 

 promoting substances and of inhibitors, the predominance of one or the 

 other being determined by various conditions. These substances influ- 

 ence the development of specific lactic acid bacteria during the spon- 

 taneous souring of milk. 



Other Substances 



Various other animal tissues and fluids contain substances which pro- 

 duce a bacteriostatic effect upon gram-positive bacteria. The method of 

 isolation of these substances and their selective action are similar to 

 those of tyrothricin (523a). 



SUBSTANCES PRODUCED BY HIGHER PLANTS 



It has been known for a long time that certain alkaloids and other 

 plant extracts possess bactericidal properties. Sherman and Hodge 

 (851) demonstrated in 1936 that the raw juices of cabbage, turnips, 

 and horseradish possess antibacterial properties. The active substance 

 in the juice could be adsorbed on activated carbon and by passage 

 through fine Berkfeld filters. The substance was thermolabile, being 

 destroyed at 60° C. in 10 minutes. 



