116 THE ACUTE SELF-LIMITED INFECTIONS 



ten minutes when in water solutions. It usually dies 

 rapidly when dried, but occasionally lives for some 

 weeks. It is killed in watery suspension by 1 per cent, 

 carbolic acid or 1 to 1000 bichloride in ten minutes. Its 

 characters in laboratory culture media are not easy to 

 describe, and indeed it often puzzles the trained observer 

 to identify it. Suspected cultures are usually subjected 

 to the Widal test, using the blood of a patient with 

 typhoid fever, and known to clump a true typhoid 



FIG. 36 



Typhoid bacillus with faintly stained flagella. (Loffler's method.) (Park.) 



bacillus. The bacillus belongs to the so-called typho- 

 colon group (see p. 164). The lower animals do not 

 develop typhoid fever when inoculated with this germ, 

 but die of septicemia, usually with peritonitis. 



Immunization. An antitoxin to the typhoid bacillus 

 cannot be produced, but attempts at active immuni- 

 zation have been made with some success. These 

 attempts take the direction of injecting the bacilli 

 in such a form that they cannot produce the disease, 



