52 INTERRELATIONSHIPS AMONG MICROORGANISMS 



Pasteur (672, 674, 675) ascribed the antagonistic effect of aerobic bac- 

 teria upon the anthrax organism to the consumption of the oxygen by 

 the former j the unfavorable influence of normal blood upon the growth 

 of anthrax was believed to be due to competition for the oxygen by the 

 red blood corpuscles. Freudenreich (299) considered the antagonism 

 between Ps. aeruginosa and Bacillus anthracis as due to exhaustion of nu- 

 trients by the former. These studies were soon followed by numerous 

 other investigations in which the exhaustion of nutrients in the media 

 was believed to be responsible for the phenomenon of antagonism j the 

 onset of the stationary phase in bacterial growth was believed (539) to 

 belong here. The change in -pW of medium and the accumulation of 

 toxic products were also found to become limiting factors. Palevici 

 (667) added fruit juice to a stale medium and brought about improve- 

 ment in bacterial growth, thus suggesting the exhaustion of growth- 

 promoting substances as the cause of staling. Broom (89) emphasized, 

 however, that the effect was due to addition of nutrients, including 

 glucose. 



It thus became apparent, even in the early days of bacteriology, that 

 certain changes are produced by microbes in the medium in which they 

 grow which render it unfit for the growth of other organisms. It also 

 was soon recognized that the problem is more complicated than the 

 mere exhaustion of nutrients. The relationships produced by changes in 

 surface tension, in oxidation-reduction potential, in reaction, and in os- 

 motic pressure were suggested as explanations (24, 627, 827). Among 

 the classical examples of the effect of reaction upon the growth of other 

 organisms is the acidification of milk by lactic acid bacteria. Metchnikov 

 emphasized the fact that Lactobacillus bulgaricus acts antagonistically 

 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 (334). 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 



