916 EXPERIMENTAL INFECTION AND IMMUNITY 



EXERCISE 20. AGGLUTININS 



EXPERIMENT 52. THE GRUBER-WIDAL REACTION IN TYPHOID FEVER 

 ("WET" METHOD). MICROSCOPIC REACTION 



1. Collect blood in a Wright capsule or small test-tube from a typhoid conva- 

 lescent patient. Rabbit immune serum may be used instead. Separate the serum 

 from the clot. 



2. Prepare two dilutions with hanging-drop slides, 1 : 50 and 1 : 100, and a culture 

 control. Use a twenty-four-hour bouillon culture of Bacillus typhosus one free of 

 clumps and in which the bacilli are long and motile. 



3. It is well to prepare a similar test with a known positive typhoid serum and 

 a normal negative serum. 



4. Dilution and slides are prepared according to the technic given in the text- 

 book. A second set of tests in dilutions of 1 : 40 and 1 : 80 may be prepared with the 

 aid of the white corpuscle pipet. 



5. Place slides away from direct sunlight and examine at the end of an hour. 

 Examinations are readily made with the % objective, the light being well cut off. 

 Examine the culture control first, then the higher and lower dilutions. 



(a) Describe the phenomenon of agglutination. 



(b) Is it necessary for all bacilli to be agglutinated to constitute a 

 positive reaction? 



(c) What are the features of a doubtful reaction? Of a negative re- 

 action? 



(d) Does the normal serum contain agglutinin for the typhoid ba- 

 cillus? 



(e) Why is it necessary to use high dilutions? What dilution is the 

 lower limit of practical safety? 



(f) Does the control show agglutination? If so, by what term is 

 this agglutination known? 



(g) What are the characteristics of a satisfactory culture for the 

 microscopic agglutination test? 



(h) Would a dead culture be serviceable in this reaction? 



(i) What practical value has the Widal reaction in the diagnosis of 

 typhoid fever? 



(j) What value has the agglutination reaction in determining the 

 degree of immunity following typhoid immunization? 



Note. If the students are immunized with typhoid vaccine, they 

 may use one another's serum in this and following experiments. 



EXPERIMENT 53. GRUBER-WIDAL REACTION IN TYPHOID FEVER 



("DRY" METHOD) 



1. Prepare smears of blood of a typhoid convalescent patient on clean glass 

 slides or collect a few drops on partially glazed paper, as prescription blanks. Allow 

 blood to dry and do not apply heat. 



