464 IMMUNOLOGY 



the fluid. Gentle shaking causes the particles to disperse and ap- 

 pear as a definite precipitate throughout the liquid. 



In the negative reaction there is no band and no precipitate. 

 The liquid usuallj^ has a faint opalescence. 



Hinton claims greater speed in testing and equal specificity 

 with the Wassermann reaction. 



Although salicylic acid and glycerol have been added apparently 

 as preservatives, the occasional growth of bacteria in the mix- 

 ture, when sterility is not accomplished, is a decided disadvantage. 

 Such contamination in tubes may be easily mistaken for positive 

 reactions. 



Citochol Reaction. — The citochol reaction of Sachs and Witeb- 

 sky appears to be gaining popularity in America. Many labora- 

 tories find it to possess a high degree of specificity and sensitivity 

 checking closely Avith other precipitation and complement fixa- 

 tion tests (Beintema, 1934, Stern, 1933, Deissler and Baker, 1935 

 and others). This reaction is similar in principle to the reac- 

 tions discussed, bearing a closer resemblance to the Kahn and 

 Meinicke. It differs from the newer precipitation tests in that 

 the authors (Sachs and Witebsky) consider the preparation of 

 the antigen comparatively unimportant. The antigen is a con- 

 centration of the Sachs-Georgi antigen used in the slower cito- 

 chol reaction. Cholesterol in concentrations of three- to six-tenths 

 per cent is used as a synergizing agent, being dissolved in the con- 

 centrated alcoholic lipoidal extract. 



Antigen.^ — The lipoidal extract is prepared by extracting one 

 part of moist beef heart with five parts of alcohol. The extract 

 is evaporated to dryness and dissolved in three volumes of alco- 

 hol. To the finished extract is added 0.3 to 0.6 per cent choles- 

 terol. A suspension is made by mixing one part of cholesterolized 

 extract with two parts of saline solution and after standing five 

 minutes, adding nine parts of saline solution, making the final 

 antigen dilution 1 :12. Nine-tenths per cent sodium chloride solu- 

 tion was originally used as a diluting fluid but the test is more 

 sensitive if 2.5 per cent sodium chloride is sul)stituted (Deissler 

 and Baker, 1935). 



Serum. — The serum is inactivated by heating at 55° C. for 

 thirty minutes. Inactivation in quantities of less than half a 



