THE WASSERMANN REACTION 621 



plete fixation in saline, i.e. it is " anti-complementary," hence 

 the need for the saline-complement series. Only the sera which 

 give partial or complete fixation in the antigen- complement 

 series need be tested with the saline- complement mixture, but it 

 generally saves time to test all the sera with the latter ; they 

 should show complete haemolysis. 



Any serum which shows partial or complete fixation in the 

 saline-complement series must be further tested. Dilutions of 

 the serum are made with saline (1-2, 1-4, 1-6, 1-8) and tested 

 with saline- complement mixture. 



The lowest dilution of serum giving complete haemolysis in 

 saline is then tested with antigen, and if this fixes the serum is 

 regarded as positive. 



Another and better method is to ascertain the limit of fixation 

 of complement in saline by testing specimens with 3, 4, 5 ... m.h.d. 

 of complement, and then to test in antigen with this dose of 

 complement 4- 1 m.h.d. complement. If there be inhibition, the 

 specimen is regarded as positive. 



A small proportion of sera which react negatively when incu- 

 bated directly in the water-bath, are found to be positive if first 

 allowed to stand at room temperature. Harrison, therefore, 

 recommends that the mixtures stand for half-an-hour before being 

 placed in the water-bath. If incubation be done in an air incu- 

 bator, this is hardly necessary, as the temperature rises slowly.] 



VIII. BEADING THE RESULTS. Complete haemolysis indicates 

 a negative, and complete inhibition a definite positive, reaction. 

 Between these two extremes, a certain number of sera will give 

 intermediate readings more or less, but not complete, haemolysis. 

 When judging between complete inhibition and slight haemolysis, 

 the opacity, rather than the colour, should be relied upon. [Some 

 place the racks in the ice chest overnight and read the results on 

 the next day.] 



[A serum giving a trace of haemolysis only may generally be 

 regarded as a weak positive. If there be partial haemolysis, no 

 inference can be made without a knowledge of the details of the 

 case. Such " partial reactions " are met with during the early 

 stages of infection, and in the course of treatment, and the test 

 should be repeated in the former case after an interval of one to 

 three weeks, in the latter after one to three months.] 



[It is useful after having ascertained that a serum is positive to 



