30 THE BIOLOGY OF BACTERIA 



lence of other bacteria is also increased by means of association. 

 The Bacillus coli is an example, for, in conjunction with other 

 organisms, this bacillus, although normally present in health in the 

 alimentary canal, is able to set up acute intestinal irritation, and 

 various changes in the body of an inflammatory nature. It is not 

 yet possible to say in what way or to what degree the association of 

 bacteria influences their role. That is a problem for the future. But 

 whilst we have examples of this association in Streptococcus and the 

 bacillus of diphtheria, B. coli and yeasts, Tetanus and putrefactive 

 bacteria, Diplococcus pneumonice and Proteus vulgaris, and Streptococcus 

 erysipelatis and Proteus vulgaris, we cannot doubt that there is an 

 explanation to be found of many, hitherto unknown, results of 

 bacterial action. This is the place in which mention should also be 

 made of higher organisms associated for a specific purpose with 

 bacteria. There is some evidence to support the belief that some of 

 the Leptotrichese (Crenothrix, Beggiatoa, Leptothrix, etc.) and the 

 Cladotricheae (Cladothrix) perform a preliminary disintegration of 

 organic matter before the decomposing bacteria commence their 

 labours. This occurs apparently in the self-purification of rivers, as 

 well as in polluted soils. 



Antagonism of Bacteria (Antibiosis). Study of the life- 

 history of many of the water bacteria will reveal the fact that they 

 can live and multiply under conditions which would at once prove 

 fatal to other species. Some of these water organisms can indeed 

 increase and multiply in distilled water, whereas it is known that 

 other species cannot even live in distilled water owing to the lack of 

 pabulum. Thus we see that what is favourable for one species may 

 be the reverse for another. 



Further, we shall have opportunity of observing, when consider- 

 ing the bacteriology of water and sewage, that there is in these 

 media in nature a keen struggle for the survival of the fittest 

 bacteria for each special medium. In a carcase it is the same. If 

 saprophytic bacteria are present with pathogenic, there is a struggle 

 for the survival of the latter. Now whilst this is in part due to a 

 competition owing to a limited food supply and an unlimited popula- 

 tion, as occurs in other spheres, it is also due in part to the inimical 

 influence of the chemical products of the one species upon the life of 

 the bacteria of the other species. Moreover, in one culture medium, 

 as Cast has pointed out, two species will often not grow. When 

 Pasteur found that exposure to air attenuated his cultures, he 

 pointed out that it was not the air perse that hindered growth, but it 

 was the introduction of other species which competed with the 

 original. The growth of the spirillum of cholera is opposed by 

 Bacillus pyogcnes foetidus. B. anthracis is, in the body of animals, 

 opposed by either B. pyocyaneus or Streptococcus erysipelatis, and yet 



