456 BACTERIOLOGY. 



phology may vary considerably, even at times when 

 grown on the same culture media, and the motility is 

 not always equally active; the flagella formation may 

 vary; the rapidity of growth may differ, especially 

 between freshly made and old cultures; the grape-leaf 

 appearance of the surface colonies on gelatin, which is 

 usually characteristic, may vary with the composition 

 of the gelatin, at times no typical colonies at all being 

 presented; the threads in the Hiss media may be lack- 

 ing; the indol test requires great care in its perform- 

 ance, and in rare instances the typhoid bacillus produces 

 it; the growth on potato is not to be depended on, being 

 often visible and not characteristic; the virulence of 

 both the bacilli is so little characteristic that it can 

 hardly be used for diagnostic purposes; and, finally, the 

 serum test is not absolutely infallible in all cases, for 

 once we met with a bacillus in feces which grew in a 

 manner utterly at variance with the typhoid bacillus, 

 yet still gave the Widal reaction perfectly with the 

 serum of an immunized horse. It is also stated by 

 Abbott that all typhoid bacilli do not give the Widal 

 reaction with the serum derived from a typhoid in- 

 fection with a single variety of a typhoid bacillus. 

 This is an experience that as yet we have not met 

 with. The Pfeiffer reaction in guinea-pigs is a matter 

 of extreme delicacy, aud varying results are sometimes 

 obtained. 



In spite, however, of these difficulties it is very easy 

 to sufficiently identify the typhoid bacillus for all prac- 

 tical purposes. A bacillus which grows typically in 

 the Hiss tube media and shows the Widal reaction with 

 a high dilution of the serum of an animal immunized 



