16 CONDITIONS MODIFYING [OH. n 



agency will abolish the power of some bacteria such as 

 B. anthracis to form spores, and may modify the character 

 of the colonies it forms (Bairibridge, 1903). 



Bacteria of the paratyphoid group agglutinate much less 

 readily after being heated (Sobernheim and Seligmann, 1910). 



(d) Differences in atmospheric pressure may modify the 

 activity of certain organisms. 



B. coli yields formic acid and gas from glucose at ordinary 

 atmospheric pressure. If the pressure is raised the yield of 

 gas diminishes but the yield of formic acid increases (Harden, 

 1901). 



A great pressure of carbon dioxide is said to deprive B. 

 anthracis of its power to form spores though it has no effect 

 on the vitality of the organism (Muir and Ritchie). 



Certain organisms which do not readily lose their virulence 

 on artificial media do so rapidly if grown in an atmosphere of 

 compressed air (ibid.). 



(e) The presence or absence of oxygen is another factor 

 of importance. Strains of B. typhoid and B. coli growing in 

 water maintain their viability better if plentifully supplied 

 with oxygen (Whipple and Mayer, 1906). 



In the absence of free oxygen B. pyocyaneus ceases to 

 produce pigment (Adami, 1892) though the spirillum rubrum 

 produces it more plentifully (Muir and Ritchie). 



Torrey (1905) observed that by alternate aerobic and 

 anaerobic culture a certain type of dysentery bacillus had its 

 power to ferment maltose greatly augmented. 



Andrewes and Horder (1906) found that a certain strepto- 

 coccus which refused to ferment lactose, under ordinary con- 

 ditions of cultivation, did so readily when deprived of oxygen. 



Kruse (quoted by Glenn, 1911) found that a staphylococcus 

 which, similarly, refused to liquefy gelatin did so at once 

 under the same altered conditions. 



Anthrax bacilli in the absence of oxygen may develop 

 torula zoogleic forms (Wood, 1889). Noguchi (1910) discovered 

 that B. biftdus communis only exhibited the bifurcating 

 phase under anaerobic conditions and in the absence of 

 oxygen became less pathogenic. 



