ANTAGONISTIC INTERRELATIONSHIPS 47 



tive chemotropism was shown to be due to thermolabile staling sub- 

 stances (358). The phenomenon of staling was often spoken of as vacci- 

 nation of medium (45), and was ascribed to the action of protein degra- 

 dation products. 



These and other experiments led to the conclusion that many micro- 

 organisms are capable of producing substances that are injurious to their 

 own development (iso-antagonistic) or, and sometimes much more so, 

 to other organisms growing close to them (hetero-antagonistic). The 

 growth of certain fungi and bacteria in practically pure culture, even in 

 a nonsterile environment, was believed to be due to this phenomenon. 

 It is sufficient to mention the lactic and butyric acid bacteria, the citric- 

 acid-producing species of As-pergillus, the lactic and fumaric-acid- 

 producing species of RMzofus, and the alcohol-producing yeasts. The 

 chemical substances produced by these organisms in natural substrates 

 may be looked upon as protective metabolic products of microorgan- 

 isms in their struggle for existence. Such products play a highly sig- 

 nificant part in the metabolism of various organisms, especially those 

 that grow parasitically upon living plant and animal bodies. 



Among the various types of antagonism, the one resulting in the pro- 

 duction of active substances that can be isolated and purified has re- 

 ceived the greatest consideration recently. These substances have been 

 designated as toxins, poisons, antagonistic agents, bacteriostatics, and 

 antibiotics. The chemical nature of some has been elucidated, but that 

 of many others is still unknown. Some of these substances are destroyed 

 by boiling, by exposure to light, or by filtration, whereas others are re- 

 sistant to heat and to ultraviolet raysj some are readily adsorbed by 

 certain filters, from which they can be removed by the use of special 

 solvents such as ether, alcohol, chloroform, and acetone. The concen- 

 tration of the antagonistic substances produced by many fungi and bac- 

 teria is greatly influenced by the energy and nitrogen sources in the 

 medium and by environmental conditions, such as temperature and 

 aeration. 



The three important types of antagonism are (a) the repressive, in- 

 hibitive, or bacteriostatic, (b) the bactericidal, and (c) the bacteriolytic. 

 When one bacterium is inoculated into the filtrate of another, the 

 growth of the first is slower than that of the control. Certain types of 



