AGGLUTINATION REACTION 



107 



a. Bouillon Culture. Many bacteria, like typhoid, paratyphoid, dysen- 

 tery, coli, etc., grow very easily in broth. Such afresh (twenty-four hours), 

 diffusely turbid culture can be employed readily for agglutination purposes. 

 In place of live bacteria, dead may also be used a fact which has greatly 

 added to the practical application of the test. 



For preparing the latter, 0.5 per cent, of phenol or i per cent, of formalin (40 per 

 cent.) are added to the twenty-four hour bouillon cultures. The result is, that a 

 sediment of bacteria is formed from which the supernatant fluid should be carefully 

 poured off. The bacterial suspension is kept on ice and thoroughly shaken before use. 



Picker has in this way prepared standard emulsions of dead typhoid and paratyphoid 

 bacilli which are sold by Merck under the name of "Ficker's Diagnosticum." 



For Widal's test, a small quantity of the patient's blood is collected in a 

 capillary tube and the end closed with sealing-wax. The blood is allowed to clot, 

 and the serum to separate off. The separation of the latter can be hastened by 

 centrifugalization. 



In practice, the Widal test as performed with Ficker's diagnosticum, is arranged as 

 follows: 



One of four results may be obtained, 

 i. 2. 



It is very advisable to make control tests with normal serum. After mixture of 

 the various ingredients the tubes are placed in the incubator at 37 C. for two hours. 

 Then the results are read off; the first tube must show absolutely no agglutina- 

 tion, otherwise (as seen in Division No. 4 above) the entire test is of no signifi- 

 cance. The cause for such spontaneous or pseudo-agglutination occurring in 

 tube i may be found either in the bacterial emulsion or NaCl solution. The grade 

 of agglutination is estimated by the size of the agglutinated clumps and the rapidity 

 with which they are formed. The mild grades of agglutination are frequently over- 

 looked by the beginner. For typhoid a positive reaction is one where agglutination 



