188 CHEMICAL NATURE OF ANTIBIOTIC SUBSTANCES 



tivity against gram-negative types. The antimicrobial action of this 

 protein can be neutralized by means of a phosphatide (1004), a reac- 

 tion which may be due to the formation of a lipoprotein that has no 

 longer any antibiotic activity. Sherman and Hodge (817) demon- 

 strated that the fresh juice of several plants has a marked bactericidal 

 effect. 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. It has been re- 

 cently demonstrated (658) that antibacterial substances are widely dis- 

 tributed among plants. 



Milk was found (657) 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. 



