NATURE OF ANTAGONISTIC ACTION 51 



not only by means of the lactic acid that it produces but also by the 

 formation of special substances. The production by bacteria of alkali- 

 reaction products that have an injurious effect upon the further growth 

 of the organisms has also been demonstrated (342). These substances 

 were found to correspond to amino compounds, liberated in the process 

 of cellular disintegration. Numerous other physical and physicochemi- 

 cal factors influence the growth of an organism in an artificial medium. 

 It is to be recalled that the rate of survival of bacterial cells in water or in 

 salt solution is markedly influenced by the colloids present, the con- 

 centration of electrolytes, the reaction, and the temperature. 



Microbial antagonism was thus looked upon largely as a result of a 

 series of physical factors, including various radiations such as mytoge- 

 netic rays, -pH changes, conductivity, electric charge, and surface ten- 

 sion (525). 



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

 antibiotic substances by the antagonists. Because of the thermolability 

 of some, sensitivity to chemical reagents, or adsorption on bacterial 

 filters, considerable difficulty has been experienced in isolating the 

 active substances. Many of these substances are iso-antagonistic, where- 

 as others are able to act upon different bacteria. Most of them have been 

 found to be thermostable. 



The first antibiotic recognized as such was pyocyanase, produced by 

 Ps. aeruginosa (235). Other organisms that produce such substances 

 are Serratia marcescens (229), Ps. jluorescens {S^^)-, B. mesentericus 

 (1052), B. mycoides, B. subtilis, and other spore-forming bacteria. 

 Since the early work at the turn of the century and especially during 

 the last five or six years, many new antibiotics have been isolated or 

 demonstrated. These will be discussed in detail later. 



The production of these antibiotics by 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, 

 whether the antagonized organisms are able to overcome their effect, 

 and whether they are destroyed by other members of the soil or water 

 microbiological population (365, 976). 



Different organisms possess different degrees as well as different 



