56 VARIATIONS IN FERMENTING POWER [CH. v 



Gaertner, B. paratyphosus B, etc. ) by growth on monochlor- 

 acetic-acid-agar, were deprived of their power to form gas 

 from glucose and other sugars ; they retained, however, their 

 power to ferment the corresponding alcohols. He found that 

 the variation in character was maintained, even on daily 

 subculture, for many " generations." 



7. The source of a strain, that is to say the nature of the 

 medium from which it is isolated, may determine certain 

 variations in fermenting power. Thus, Revis (1908) found that 

 strains of B. coli cultivated from milk were frequently able 

 to ferment saccharose. Moreover a strain obtained from 

 cow dung, which was unable to ferment saccharose, acquired 

 the power to do so after being grown in milk. Wilson (1909) 

 found that many coliform organisms isolated from urine had 

 lost the property of forming gas from dextrose. Adami, 

 Abbott and Nicholson (1899) describe strains of B. coli grown 

 in ascitic fluid as being unable to ferment glucose or dextrose 

 broth this power being only partially regained after three 

 passages through the guineapig. 



IV. Symbiosis may influence fermenting power. 



Major Horrocks's experiments (1911) are of interest in 

 this connection. He found in two experiments 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 

 the urine of a "typhoid carrier." In one case reversion in 

 character took place on further subculture. He found, in 

 a third experiment, that a strain of B. typhosus derived 

 from the urine of a " carrier," lost both its fermenting and 

 its agglutinating properties when grown in the diluted, filtered 

 urine of another "typhoid carrier." 



V. Variation in fermenting power is found in organisms 

 isolated from " carriers." 



The strain of B. typhosus isolated by Wilson from the 

 urine of a " typhoid carrier '' was found to have acquired the 

 power to ferment lactose and saccharose, and the power also 

 to produce "much gas" from mannite and maltose. 



