CH. 11] THE CHARACTERS OF BACTERIA 23 



inimical to the growth of the Klebs-Loeffler bacilluB (Smirnow, 

 1908). 



Prescott and Baker (1904) describe a similar antagonism 

 between streptococci and B. eoli and they attribute the 

 extinction of the latter when the two are grown together to 

 the greater sensitiveness of B. coli to the lactic acid produced 

 by both combatants. 



Klein (1903-4) found that a strain of B. typhosus was 

 killed by B. coli in the peritoneal cavity and Horrocks (1911) 

 found that the same thing happened in water which contained 

 both organisms. Jordan, Russell and Zeit (1904) observed 

 that B. typhosus quickly died out in polluted water. 



Symbiosis is observed to influence not only the viability of 

 bacteria but their virulence, their morphology, their fermenting 

 powers, -and other characters. The presence of the strepto- 

 coccus is said to be inimical to the growth of the diphtheria 

 bacillus (Smirnow, 1908) but it increases the virulence of the 

 latter during "passage" (Muir and Ritchie, 1910) while on 

 artificial media it induces changes in the morphology of the 

 bacillus, "granular" forms appearing earlier than in a pure 

 culture (Denny, 1903). Smirnow (1908) observed that the 

 same bacillus grown on agar in the presence of a bacillus 

 isolated from an acute rhinitis, assumed a coccic form — 

 retaining, however, its virulence unimpaired. The meningo- 

 coccus produced a similar change. 



Lesieur (1901, quoted Clark, 1910) claimed that the pseudo- 

 diphtheria bacillus may assume the morphological characters 

 of the Klebs-Loeffler bacillus as a result of symbiosis with 

 aurococcus aureus. 



Horrocks (1911) found that a typical strain of B. typhosus 

 lost its power to ferment "sugars" when grown in the presence 

 of a strain of B. coli derived from a typhoid carrier (vide 

 p. 119). 



In some cases bacteria growing together are able to produce 

 results which neither can do alone. For example, neither 

 B. coli nor B. dentrifieans alone can reduce nitrates, but if 

 allowed to act on sodium nitrate together they bring about the 

 escape of free nitrogen (Marshall Ward and Blackman, 1910), 



