NATURE OF ANTAGONISTIC ACTION 53 



salt solution is markedly influenced by the colloids present (991), the 

 concentration of electrolytes (816), the reaction (897), and the tem- 

 perature (36). 



Microbial antagonism was thus looked upon (496) largely as a re- 

 sult of a series of physical factors, including various radiations such as 

 mytogenetic rays (9, 679, 814), fH. changes, conductivity, electric 

 charge, and surface tension. 



Most antagonisms, however, can be explained by the production of 

 toxic substances by the antagonists. Because of their thermolability, 

 sensitivity to chemical reagents, or adsorption on bacterial filters, con- 

 siderable difficulty has been experienced in isolating the active sub- 

 stances. Many of these substances have been found to be iso-antagonistic 

 (autotoxins [141]), whereas others are able to act upon different bac- 

 teria. Most of them have been found to be thermostable. 



The first antibiotic substance recognized as such was pyocyanase 

 (235), soluble in alcohol, ether, and chloroform. Somewhat similar 

 substances appear to be produced by Serratia marcescens ( 230) , Ps. fluo- 

 rescens {s2S)jB. mesentencus ( 10 1 6) , and Bacillus mycoides. Whereas 

 Emmerich and Low (236) considered pyocyanase to be a proteolytic 

 enzyme, others (370, 410, 668, 679) found it to be a lipoid. Since that 

 early work and especially during the last five years, many new agents 

 have been isolated or demonstrated. These will be discussed in detail 

 later. It is sufficient to mention gramicidin and tyrocidine, produced by 

 B. brevis, which are polypeptides 5 citrinin and fumigatin, which are 

 quinone-like in nature j actinomycin, aspergillic acid, and iodinin, which 

 are nitrogenous ring compounds j gliotoxin, which is a sulfur-bearing 

 compound J streptothricin, streptomycin, and proactinomycin, which are 

 nitrogenous bases. Some of the most important compounds (penicillin) 

 have not as yet been sufficiently elucidated. Certain microbial pigments 

 (pyocyanin, hemipyocyanin, prodigiosin) have also received considera- 

 tion as bacteriostatic and fungistatic agents. 



The production of antibiotic substances by various microorganisms is 

 greatly influenced by reaction, temperature, and aeration of substrate, 

 as well as by the presence of other organisms. Evidence is still lacking 

 as to whether these substances may accumulate in the soil and in water 



