TYPHOID BACILLUS 



171 



produces death by (i) profound toxaemia; (2) ulceration of the 

 Peyer's patches, causing perforation and peritonitis; (3) by the 

 destruction of a blood-vessel in the floor of an ulcer producing a 

 haemorrhage. 



In animals, as a rule, typhoid bacilli if injected, produce no 

 disease, and the bacilli rapidly die. In chimpanzees, how- 

 ever, it is possible to produce atypical typhoid lesions and 

 symptoms. 



Natural and Acquired Immunity. Human blood serum is 

 strongly bactericidal toward the typhoid bacillus. Normal gas- 

 tric juice, with its hydrochloric acid, destroys 

 the bacillus when ingested and this forms the 

 natural means of protection. Immunity fol- 

 lowing an attack of typhoid is generally of 

 long duration. If bacilli do reach the blood- 

 stream of an immune individual, the ambo- 

 ceptors originated by a previous infection, 

 together with the complement normally pres- 

 ent, effect a solution of the invading organism. 

 For vaccination against typhoid fever see 

 page 80. Anti-serum for typhoid has been 

 prepared by injecting horses with killed 

 culture of typhoid bacilli, but it has not 

 proved to be effective. 



Agglutinations. One of the most important means of diagnos- 

 ing typhoid fever is by the so-called Widal test, really the Gruber 

 and Durham agglutination reaction. This consists in applying 

 the serum of the blood of a person, supposedly ill with typhoid, 

 to a fresh bouillon culture of typhoid bacilli. If the person has 

 the disease, and it has lasted for five or more days, the bacilli are 

 promptly agglutinated in clumps. Undiluted normal serum, and 

 serum from people suffering other diseases, will bring about the 

 same reaction at times; it is therefore best to dilute the serum 

 with water 1-50, and if the reaction comes within an hour the 



FIG. 48 Widal 

 reaction. One-half 

 of the field shows 

 typhoid bacilli un- 

 clumped, other half 

 shows clumping. 

 (Greene's Medical 

 Diagnosis.) 





