34 LABORATORY COURSE IN SERUM STUDY 



this purpose. It must be remembered that no two suspensions 

 of red cells are exactly alike since it is impossible to measure 

 them with absolute accuracy, and since the resistance of erythro- 

 cytes to haemolysis, even when taken from the same animal on 

 different days, may vary. No two fresh sera, moreover, are 

 entirely alike in alexic activity. The experiments given below 

 will demonstrate the method of determining by titration the 

 minimal hsemolytic dose of complement and amboceptor ; they 

 will also demonstrate that this dose varies reciprocally, that is, 

 that with a smaUamount of complement a relatively larger 

 amount of amboceplor will be necessary to cause complete 

 haemolysis, whereas with a large amount of complement only a 

 small amount of amboceptor is necessary. There is, however, no 

 simple proportionality. 



Experiment 1 



TITRATION OF HJSMOLYTIC SENSITIZER OR AMBOCEPTOR. DETERMINA- 

 TION OF UNIT 



The unit of sensitizer, or amboceptor, is the smallest amount 

 which will cause complete laking of a unit of cells (1.0 c.c. of a 

 5 per cent emulsion) 1 in one hour, no matter how much comple- 

 ment is used, i.e., in the presence of an excess of complement. 



As the degree of dilution is an important factor it is necessary that 

 the volume of all the tubes be brought to a uniform standard before 

 the reaction actually begins. For this reason the reagents are added in 

 the following order : 



1. Sensitizer [amboceptor] 



2. Alexin [complement] 



3. Saline to make all volumes equal 



4. Cells 



A control tube must be set up to prove that the amount of alexin or 

 complement used will not of itself lake the cells. 



1 For convenience or economy 0.5, 0.25 or 0.1 c.c. of 5 per cent red cells are 

 sometimes taken as the unit, and in such cases the unit of amboceptor and com- 

 plement must be proportionately reduced. For the sake of uniformity results 

 so obtained can easily be transposed to terms of the 1 c.c. unit, as is often done 

 in reporting Wassermann tests. 



