234 PUBLIC HEALTH BACTERIOLOGY 



is believed to reduce the case incidence and the mortality 

 among vaccinated persons attacked. 



Vaccine treatment of typhoid fever on similar lines has 

 been tried by Leishman and Smallman, using one-fifth of 

 the dose used for protective inoculation. If the tempera- 

 ture fall, the injection may be repeated every four days. 

 Antityphoid serum has been used, but results are equivocal. 



Agglutination. The blood or blood serum of an animal 

 previously inoculated with typhoid bacilli, when added to 

 a suspension of living and motile typhoid bacilli, causes 

 the latter to become motionless and aggregated (clumped) . 

 This reaction is one given in many diseases after the 

 attack a reaction of immunity ; but in enteric fever it is 

 given during the attack a reaction of infection. The 

 reaction is specific in high dilutions, but not absolutely 

 so. Group bacilli are clumped, but in lower dilutions : 

 for example, serum clumping typhoid bacilli in a dilution 

 1-40,000 will clump paratyphoid bacilli in a dilution 

 i-iooo, and coli bacilli in 1-500. The reaction is used 

 for : (i) Diagnosis of disease (Widal's reaction) ; and 

 (2) Diagnosis of bacteria (Grueber's reaction). 



1. Widal's Reaction. 



a. Microscopic method. Requirements : An eighteen to 

 twenty-four hours' culture in broth of undoubted B. 

 typhosus. Blood or serum. Platinum loop, a hollow 

 ground slide, an ordinary slide or a watch-glass, cover- 

 slips, a one-sixth-inch lens, and vaseline. 



PROCEDURE. i. Test motility of bacilli and absence of 

 clumping by putting up a hanging drop of culture. If 

 clumps, filter. If movements sluggish, warm. 



2. Take a clean dry slide and put on it nine loopfuls of 

 sterile broth arranged in a small circle. Put one loopful 

 of serum in centre of circle and mix. Dilution i-io. 

 Now put one loopful of i-io dilution on a clean slide or 

 hollow slide, mix with three loopfuls of sterile broth, and 

 finally with one loopful of culture. Dilution is now 1-50. 



3. Mount one loopful on a cover-slip, invert over hollow 

 slide, and examine. Examine again in fifteen minutes and 

 after one hour. If reaction is positive, the bacilli will be 

 arranged in groups and be non-motile, and between the 

 clumps will be clear spaces. 



