MACROSCOPIC AGGLUTINATION REACTION. 



99 



tery, coli, etc., grow very easily in broth. Such a fresh (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 obtaining 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. 



Ficker 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 carrying out Widal's test, a small quantity of the patient's blood is collected 

 into 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 centri- 

 fugalization. 



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

 follows: 



One of four results may be obtained. 



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

 of the various ingredients the tubes are placed into the incubator at 37 for two hours. 

 Then the results are read off and the first tube must show absolutely no agglutination 

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



