98 AIDS TO BACTERIOLOGY 



facultatively anaerobic and Gram-negative It is not 

 killed by drying ; its thermal death-point is 55 C. Diffused 

 daylight prevents its development, and direct sunlight is 

 fatal in five hours. 



The typhoid bacillus usually carries eight to twelve 

 flagella arranged round its sides and end. It is actively 

 motile, and in hanging-drop preparations some of the 

 organisms are seen to progress at a surprisingly rapid rate- 

 while others rotate rapidly. While growth is best at 

 blood-heat, the bacillus develops well at room tempera- 

 ture, though less quickly than does the colon bacillus. 



Cultural Characters. On agar the typhoid bacillus 

 produces a thick, greyish, creamy layer. On gelatin it 

 gives a white, thin growth, usually almost confined to the 

 needle track, and without liquefaction. In a gelatin shake 

 culture the growth forni^> a diffuse haziness, without any 

 gas-bubbles. The surface colonies in gelatin plates are 

 small (1 millimetre), semi-transparent, bluish- white in 

 colour, with an irregular outline; the deep colonies are 

 roundish points with sharp margins, finely granular, and 

 yellowish- brown in colour. In broth a general turbidity 

 is produced, with some deposit, but no pellicle. Milk is 

 rendered slightly and permanently acid, but there is no 

 curdling. Occasionally alkalinity may succeed acidity if 

 culture in milk be prolonged. On slightly acid potato 

 a thin, moist, greyish, almost invisible layer is formed. 

 Glucose and mannite are fermented with the production 

 of acid only, no gas, but lactose and saccharose are un- 

 attacked. It forms no indole, does not give the Voges- 

 Proskauer reaction, and neutral red is unaltered. 



Strains of typhoid bacilli showing slight divergence in 

 some cultural character from typical attributes are met 

 with. We found a carrier strain to slowly ferment lactose 

 with production of acid (in three days) (see also p. 28). 



Strains grown on lactose, dulcite, or arabinose acquire 

 the power of fermenting the respective carbohydrate or 

 alcohol to which they have been ' educated,' but many 

 educated strains quickly revert to the non-fermenting 

 typical organism. 



Channels of Infection Water. Although water con- 

 taminated with sewage may be drunk with impunity, 

 should the dejecta of a case of typhoid contribute to the 

 pollution, an epidemic of typhoid may be expected. In 



