E. A. Watson 
161 
will not endanger the life of the animal—about 25 c.c. The rabbits 
are then kept in reserve and can easily be reimmunized as required. 
Finally, the serum is separated from the corpuscles and stored in 
very small ampoules—0-2 c.c. in each ampoule for convenience and 
economy—in the ice chamber. 
When the serum is not to be used immediately it requires neither 
inactivation nor carbolization, and is, in fact, better without, the index 
remaining constant or but very slightly lowered even after six months. 
But unless the serum has been collected under aseptic conditions, 
rather than risk it spoiling, TO c.c. of the carbolized glycerine preser¬ 
vative is added to 9-0 c.c. of serum before measuring it into the ampoules. 
The whole procedure of immunizing rabbits, drawing blood from the 
heart, separating and bottling serum, can and should be carried out 
under aseptic conditions. 
(c) Complement. Normal guinea-pig serum in a fresh state furnishes 
a rich complement. Blood may be drawn from the heart, if desired, 
but as guinea-pigs are usually plentiful at a laboratory it is simpler to 
anaesthetize the animal in an ether jar, remove and suspend the 
guinea-pig over a centrifuge tube of 25 or 30 c.c. capacity, sever the 
arteries and veins on one side of the neck, and collect all the blood. 
Centrifuge immediately, before coagulation takes place. The clear 
serum is taken off and placed in the ice chamber. Complement is always 
better used in the fresh state so the guinea-pig should not be bled until 
just before complement is needed for a titration or a diagnostic test. 
B. Dourine ( antibody ) combining group. 
( x) Antigen. A stock dourine antigen is obtained as the result of 
inoculating a number of white rats with Trypanosoma equiperdum, 
collecting the rat’s blood when teeming with trypanosomes, and separa¬ 
ting the trypanosomes from blood cells and serum by washing and 
centrifuging. 
The blood of a dourine infected rat is collected in a vessel containing 
sufficient salt solution to prevent coagulation. Not less than ten large 
white rats—twenty or twenty-five rats, if a considerable amount of 
antigen is needed—are inoculated intraperitoneally with the diluted 
blood, injecting an equal amount, about 0*3 c.c., into each rat. This may 
be done very conveniently by taking a small sharp-pointed pipette, with 
rubber tubing and mouthpiece attached, drawing the blood up to a point 
