358 



TYPHOID FEVER 



the agar are small, and appear as minute round points. Under a 

 low objective, the surface colonies are found to be very transparent 

 (requiring a small diaphragm for their definition), finely granular 

 in appearance, and with a very coarsely crenated and well- 

 defined margin. The deep colonies are usually spherical, some- 

 times lenticular in shape, and are smooth or finely granular on 

 the surface, and more opaque than the superficial colonies. In 

 cover-glass preparations, the bacilli are found to present the same 

 microscopic appearances as in preparations from solid organs, 

 except that there may be a greater number of the longer forms 

 which may almost be called filaments (Fig. 107). The same is 



true of films made from 

 young gelatin cultures. 

 Sometimes the diversity 

 in the length of the 

 bacilli is such as to throw 

 doubt on the purity of 

 the culture. As a general 

 rule, in a young (twenty - 

 four or forty-eight hours 

 old) culture, grown at a 

 uniform temperature, the 

 bacilli are plump, and 

 the protoplasm stains 

 uniformly. In old cul- 

 tures, or in cultures 

 which have been exposed 

 to changes of tempera- 

 ture, the protoplasm 

 stains only in parts ; 

 there may be an appear- 

 ance of irregular vacuolation either at the centre or at the ends 

 of the bacilli. 



Motility. In hanging-drop preparations the bacilli are found 

 to be actively motile. The smaller forms have a darting or 

 rolling 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. 110), the bacilli are seen to possess many long wavy 

 fiagella which are attached all along the sides and to the ends 



FIG. 107. Typhoid bacilli, from a young 

 culture on agar, showing some filamentous 

 forms. 



Stained with weak carbol-fuschin. x 1000. 



