322 



TYPHOID FEVER. 



length of the bacilli is such as to throw doubts on the purity of 

 the culture. Its purity, of course, can be readily tested by pre- 

 paring plates from it in the usual way. As a general rule in a 



young (twenty- 

 four to forty- 

 eight hours old) 

 colony, grown 

 at a uniform 

 temperature, 

 the bacilli are 

 plump, and the 

 protoplasm 

 stains uniform- 

 ly. In old cul- 

 tures or in cul- 

 tures which 

 have been ex- 

 posed tochange 

 of temperature, 

 the protoplasm 

 stains only in 

 parts; there 

 may be an ap- 

 pearance of irregular vacuolation either at the centre or at the 

 ends of the bacilli. There is no evidence that spore formation 

 occurs in the typhoid bacillus. 



Motility. — In hanging-drop preparations the bacilli are found 

 to be actively motile. The smaller forms have a darting Or roll- 

 ing motion, passing quickly across the field, whilst some show 

 rapid rotatory motion. The filamentous forms have an undu- 

 lating or serpentine motion, and move more slowly. Hanging- 

 drop preparations ought to be made from agar or broth cultures 

 not more than twenty-four hours old. In older cultures the 

 movements are less active. 



Flagella. — On being stained by the appropriate methods (^'x^/i? 

 p. 107) the bacilli are seen to possess many long wavy flagella 

 which are attached all along the sides and to the ends (Fig. 1 15). 

 They are more numerous, longer, and more wavy than those of 

 the B. coli. 



Characters of Cttltitrcs. — Stab-cultures in peptone gelatin give 



Fig. 115. — Tjq^hoid bacilli, from a young culture on agar, showing 

 flagella. Stained by Van Ermengem's method. X looo. 



