454 



YELLOW FEVER. 



B. coli group. It has rounded ends, is 2 to 4 ^ long, about 

 .5 /j. broad, often occurring in pairs (Fig. 117), staining by 



* i 



\ 



FIG. 117. Bacillus Icteroides, from a 

 young culture on agar (Sanarelli). x 1000. 



the ordinary stains but decolorised 

 in Gram's method. It is motile and 

 possesses 4 to 8 flagella. It grows 

 on all the usual media ; on gelatine 

 plates after twenty -four hours the 

 colonies are minute points some- 

 what transparent to the naked eye, 

 and under a low power have a finely 

 granular appearance. After six or 

 seven days there appears somewhere 

 in the colony a focus of more active 

 growth, forming an opaque centre, 

 from which granular striae radiate to 

 the periphery. The gelatine is not 

 liquefied. The most characteristic 

 growth is that in sloped agar. After 

 twenty-four hours at 37 C. there is 



a grey iridescent and somewhat transparent growth. On 

 being transferred to a temperature of 20 C. to 28 C. this 



FIG. 1 1 8. Culture 

 of Bacillus Icteroides 

 on agar, showing the 

 characteristic appear- 

 ance when incubated 

 at the two temperatures 

 mentioned (Sanarelli). 



Natural size. 



