E. A. Watson 
179 
The prevention or inhibition of haemolysis may be complete, partial 
or slight—according to the richness of the serum in specific antibodies. 
However, with the standard doses of serum, in the great majority of 
cases, the reaction is either clearly positive or clearly negative. 
Occasionally, complement fixation complete with 0-2 c.c. serum, partial 
with 0-15 c.c. and slight with 0-1 c.c. may be given. This is a positive 
reaction and indicates that the serum is weak in antibodies, only one 
unit being present in 0-2 c.c. serum. 
Partial fixation with 0-2 serum and complete haemolysis with 0-1 
serum is a rare reaction and of a questionable nature. In the serum 
controls, without antigen, haemolysis should always be complete. 
Very rarely indeed it happens that haemolysis in the serum controls 
is not complete, the mixture having a cloudy or opaque appearance and 
some of the red cells remaining unhaemolysed. This may be the result 
of insufficient inactivation or of changes in the serum due to certain 
bacterial growths. When such questionable reactions are given a 
fresh specimen of serum is asked for and a retest made. 
General Remarks. 
The successful practice of the complement fixation test depends 
mainly upon the preparation and use of powerful reagents, their 
specificity and the accurate determination of their relative values, the 
fixing of standard doses wherever possible, and a constant, uniform 
technique and method of procedure. 
Close familiarity with the activity of the reagents is essential for 
the best results. 
Stock reagents should be prepared in quantities calculated to meet 
all requirements for as long a time as the activity of the reagents remains 
practically constant. Thus: sufficient haemolytic serum for six months’ 
work; antigen to suffice for one month’s work; fresh red cell suspension 
once a week; fresh complement daily or on alternate days, or as needed. 
It is advisable to use the blood of two sheep for sensitizing rabbits and 
to use the red cells of the same sheep for the haemolytic system. 
The following points of extreme importance will bear repetition: 
(1) The amount of red cells in suspension must be very accurately 
measured and the standard amount never varied. 
(2) The use of the least possible amount of complement which 
with two units of haemolytic serum causes complete haemolysis of red 
cells. 
