462 IMMUNOLOGY 



dispersion is prepared by heating the ingredients to 55° C. in a 

 water bath and pouring the saline solution into the antigen. 

 Thorough mixing is accomplished by pouring back and forth ten 

 times. The diluted antigen is ready for immediate use. 



Serum.^ — The serum is obtained in the usual manner. It mud 

 not be inactivated. 



Technique of the Test. — Place 0.2 c.c. of active (raw) serum 

 in a small test tube of the Kahn type and add 0.5 c.c. of freshly 

 prepared suspension (M.K.R.II suspension). Mix the ingredients 

 thoroughly and incubate at room temperature. 



Interpretation of Results. — According to Meinicke the test 

 can be read by any of the four methods outlined in the following 

 discussion. It has been our experience that the macroscopic floc- 

 culation method is the safest procedure to follow when testing 

 weakly positive sera. In our hands the test has no distinct ad- 

 vantage over the Kalm and Kline tests. The four metliods of 

 i-eading the test are : 



1. Macroscopic flocculation reaction: The flocculation is I'cad 

 like an agglutination reaction after one and one-half hours of 

 incubation. Using a hand lens distinct clumps are present in 

 positive serum which are absent in a negative reaction. 



2. Microscopic reaction : A few drops of the liquid are removed 

 from the serum-suspension mixture when it is set up and placed 

 in a paraffin ring on a slide. This is incubated for one hour in 

 a moist chamber. 



When magnified sixty diameters, clumps indicate a positive 

 reaction which are absent in the negative serum. 



3. Clarification reaction: Incubate tubes overnight at room 

 temperature. Negative reaction remains uniformly turbid. The 

 degree of clearing of the supernatant liquid indicates the strength 

 of the positive reaction with a strong positive reaction becoming 

 completely clear. 



4. Centrifugal technique : TJie tubes are centrifuged at low 

 speed for ten minutes immediately after setting up the test. The 

 speed can be determined by trial for each centrifuge, which will 

 exclude nonspecific reactions (Dombrowsky, 1933). All super- 

 natant liquid is poured out and the tubes are inverted for half an 



