132 METHODS OF EXAMINING SERUM 



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1. We add to a small test-tube 



(a) '05 c.c. of serum from the suspected case, heated for half 

 an hour at 55 C. to destroy the human complement, and '5 c.c. 

 of "8 per cent, salt solution ; 



(b) "I c.c. of an alcoholic extract of guinea-pig's or ox's liver 

 (this can be prepared by extracting finely minced liver with four 

 volumes of alcohol for 3 to 4 days and then filtering) ; 



A certain amount of guinea-pig's serum, usually '1 c.c., to 

 act as complement. 



The mixture is then placed in the incubator for one and a half 

 hours, to allow fixation of complement to occur. 



2. We then add to the tube 1 c.c. of a 5 per cent, suspension 

 of sensitised corpuscles (usually sheep's or ox's), i.e. corpuscles 

 to which there has been added a sufficient quantity of immune 

 serum to produce lysis on the addition of complement. 



The mixture is then placed in the incubator for another hour. 

 If lysis of the corpuscles does not occur, the complement has 

 been fixed in the first stage by the mixture of serum and liver 

 extract. This is a positive result, and indicates the presence of 

 syphilis. If the corpuscles undergo lysis, all the complement 

 has not been fixed the result is negative. When the amount 

 of serum to be tested is small, the amounts given may all be 

 proportionately reduced. 



Such is the test as usually performed, and in this form it 

 usually gives satisfactory results. It is to be noted, however, 

 on the one hand, that the liver extract alone may fix a certain 

 amount of complement, rarely more than three doses, and, on 

 the other hand, that the hsemolytic value of fresh serum varies, 

 i.e. the amount of complement is not always indicated by the 

 volume of serum. It is accordingly better, and in a laboratory 

 this can be readily done, to estimate the hamiolytic dose of the 

 guinea-pig's serum, and to prepare a series of tubes, each con- 

 taining the same amounts of serum and of liver extract, but 

 with a different number of doses of complement in each tube. In 

 this way we can find the number of doses of complement deviated 

 in each case. As controls, the effect of the extract alone and of the 

 serum alone can be tested at the same time. With the amounts 

 of extract and serum mentioned, a positive result indicating the 

 presence of syphilis may be accepted when five or more doses of 

 complement are deviated in addition to the amount absorbed in 

 the controls. Some observers use the same amount of comple- 

 ment in each tube, but vary the amounts of suspected serum, and 

 in this way some idea of the deviating power of the serum is 

 obtained, but we consider that the method given is to be preferred. 



