360 



TYPHOID FEVEK 



rence of groups of bacilli lying between the cells of the tissue 

 (Fig. 105). The individual bacilli are 2 p to 4 ft long, with 

 somewhat oval ends, and - 5 /* in thickness. Sometimes fila- 

 ments 8 /j. to 10 //. long may be observed, though they are 

 less common than in cultures. It is evident that one of the 

 bacilli may frequently in a section be viewed endwise, in which 

 case the appearance will be circular. This appearance accounts 

 for some, at least, of the coccus-lite forms which have been 

 described. The bacilli are Gram-negative. 



Isolation and Appearances of Cultures. — To grow the 

 organism artificially it is best to isolate it from the spleen (for 



metho'd, see p. 141), as it 

 exists there in greater 

 numbers than in the 

 other solid organs, and 

 may be the sole organism 

 present even some time 

 after death. Agar . or 

 MacConkey lactose plates 

 may be employed. On 

 the agar media the 

 growths are visible after 

 twenty-four hours' incu- 

 bation at 37° C. On 

 MacConkey plates the 

 colonies are small, colour- 

 less, and dewdrop-like. 

 On agar plates the super- 

 ficial colonies are thin 

 and film-like, circular or 

 slightly irregular at the 

 margins, dull white by reflected light, bluish-grey by trans- 

 mitted light. Colonies in the substance of 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. 106). Sometimes 



Fig 



106. — Typhoid bacilli, from a yonng 

 culture on agar, showing some filamentous 

 forms. 

 Stained with weak carbol-fuchsin. x 1000. 



