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- 



' - e '""-.*'/".'_ - J 



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 to change 

 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 (vide 

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

 which are attached all along the sides and to the ends (Fig. 115). 

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

 the B. coli. 



Characters of Cultures. Stab-cultures in peptone gelatin give 



FlG. 115. Typhoid bacilli, from a young culture on agar, showing 

 flagella. Stained by Van Ermengem's method. X 1000. 



