372 



TYPHOID FEVER 



cover-glass preparation shows numerous bacilli. Later, however, 

 a slight pellicle with a dull, somewhat velvety surface may 

 appear, and this may even assume a brown appearance. These 

 characteristic appearances are only seen when a fresh potato with 

 an acid reaction has been used. 



In bouillon incubated at 37 0. for twenty-four hours there 

 is simply a uniform turbidity. Cover-glass preparations made 



from such sometimes 

 show filamentous forms 

 of considerable length 

 without apparent seg- 

 mentation. 



Conditions of Growth, 

 etc. The optimum tem- 

 perature of the typhoid 

 bacillus is about 37 C., 

 though it also flourishes 

 well at the room tem- 

 perature. It will not 

 grow below 9 C. or 

 above 42 C. Its powers 

 of resistance correspond 

 with those of most non- 

 sporing bacteria. It is 

 killed by exposure for 

 half an hour at 60 C., 

 or for two or three 

 minutes at 100 C. Typhoid bacilli kept in distilled or in ordinary 

 tap water have usually been found to be dead after three weeks 

 (Frankland). 



Biological Reactions. Very important means of identifying 

 the typhoid bacillus are found in testing its capacities for growth 

 on certain special media. This facilitates its being differentiated 

 from the b. coli and the other members of the coli-typhoid group. 

 The following results will be best appreciated if considered in 

 relation to what is said regarding these other organisms, as the 

 reactions of the typhoid bacilli in differentiating media are 

 largely negative. (See Table, p. 407.) 



The tests with sugars are important. The typhoid bacillus 

 produces acid without gas in maltose, laevulose, glucose, and 

 mannite, but originates no change in lactose, cane-sugar, or 

 dulcite ; in the last, however, acid formation may appear after 

 some weeks. Further, no gas production is observed in gelatin 

 shake cultures, and there is no curdling of milk, although in 



PIG. 114. Colonies of the typhoid bacillus 

 (one superficial and three deep) in a gelatin 

 plate. Three days' growth at room tem- 

 perature, x 15. 



