BACILLUS OF TYPHOID FEVER 403 



The aim has been chiefly the differentiation of typhoid bacilli from the 

 bacilli of the colon group, and most of the media have been devised with 

 this end in view. (See section on Media.) 



Rothberger l has devised a mixture of glucose agar to which is added 

 one per cent of a saturated aqueous solution of neutral-red. Shake-cul- 

 .tures or stab-cultures are made in tubes of this medium. The typhoid 

 bacillus causes no changes in it, while members of the colon group, by 

 reduction of the neutral-red, decolorize the medium and produce gas by 

 fermentation of the sugar. 



Utilizing the fact that bile-salts are precipitated in the presence of 

 acids, Macconkey devised a medium composed of sodium glycocholate, 

 pepton, lactose, and agar (the composition of this medium is given on 

 page 138), in which Bacillus typhosus grows without causing much 

 change, but distinct clouding results from the growth of the colon bacillus 

 which, producing acid from the lactose, causes precipitation of the bile- 

 salts. 



On Wurtz's lactose-litmus-agar (see page 129) the typhoid bacillus 

 produces no acid, but eventually deepens the purple color to blue; 

 the colon bacillus produces acid and in stab-cultures gas bubbles and 

 the color changes to red. 



In Barsiekow's (see page 139) lactose-nutrose-litmus mixture the 

 typhoid bacillus causes no change, while the colon bacillus produce? 

 coagulation and an acid reaction. 



Cultural Differences Within the Typhoid Group. Recent work by 

 H. Weiss in this laboratory has shown that not all typhoid bacilli are 

 culturally alike, there being two distinct groups, one which ferments 

 xylose and the other which does not. This work is being elaborated. 

 Since there are also antigenic differences it may be necessary in the 

 future to speak rather of a typhoid group than of the typhoid bacillus. 



Biological Considerations. The typhoid bacillus is an aerobic and 

 facultatively anaerobic organism growing well both in the presence and in 

 the absence of oxygen when certain sugars are present, showing a slight 

 preference, however, for well aerated conditions. It grows most luxu- 

 riantly at temperatures about 37.5 C., but continues to grow within a 

 range of temperature lying between 15 and 41 C. Its thermal death 

 point, according to Steinberg, is 56 C. in ten minutes. It remains alive 

 in artificial cultures for several months or even years if moisture is sup- 

 plied. In carefully sealed agar tubes Hiss has found the organisms 



* Rothberger, Cent. f. Bakt., xxiv, 18Q8. 



