RELATION TO ENVIRONMENT— CLASSIFICATION 31 



This behavior is due to the influences which various microorganisms 

 exert upon each other and is known as antagonism. Such antagonism 

 probably depends upon the fact that the metabohc products of the pre- 

 dominant species (the one or ones for whom the special cultural condi- 

 tions are most favorable) inhibit the growth of the less vigorous varieties. 

 Many examples, experimentally supported, of such antagonism, can be 

 given. Thus, the gonococcus is distinctly inhibited by the soluble pro- 

 ducts of Bacillus pyocyaneus,' while in the presence of pyogenic cocci it 

 develops luxuriantly, and the baciUus of plague is completely inhibited 

 when streptococci are present in the culture.^ 



Mutual inhibition may also be due to the monopolizing of the nutri- 

 tion in the medium by the predominating species or to the change in re- 

 action produced by its growth. This last consideration is probably the 

 secret of the frequently noticed inhibitory effect exerted by acid-pro- 

 ducers upon bacteria of putrefaction, and has received practical thera- 

 peutic appUcation in Metchnikoff's lactic-acid bacillus therapy, which 

 see. 



When the simultaneous presence of two bacterial species within the 

 same environment favors the development of both species, the condi- 

 tion is spoken of as symbiosis. Such dependence is not so frequent as 

 antagonism, but it does occur. Examples of such a condition have been 

 observed in cultures containing diphtheria bacilli and streptococci ' and 

 have been frequently observed in cultures containing both aerobic and 

 anaerobic bacteria, where the former favor the development of the latter 

 by monopolizing the supply of free oxygen. Symbiosis may also take 

 place in cultures in which complex food products are split up by one 

 species, furnishing substances for ingestion by species with a lesser 

 digestive ability. 



RELATIONS OF BACTERIA TO PHTSICAL ENVIRONMENT 



Relation to Temperature. — Like all other living beings, bacteria 

 develop and multiply by virtue of a series of chemical and physical 

 processes, by means of which growth energy is obtained by destruction 

 or catabolism, and the lost tissues resupplied by absorption of nutritive 

 materials. It is natural, therefore, that the conditions of external 



' Schafer, Fortsehr. d! Med., 5, 1896. 



2 Bitter, Rep. Egypt Plague Com., Cairo, 1897. 



^HilbeH, Zeit. f. Hyg., xxix, 1895. 



