104 APPLIED IMMUNOLOGY 



approximately of one-half serum and one-half cor- 

 puscles. To make up a 5 per cent, suspension there- 

 fore, 1 c.c. of the defibrinated blood is placed in a 

 graduated centrifuge tube by means of a 1 c.c. pipette, 

 and the contents of the tube brought up to 10 c.c. by 

 the addition of normal salt solution. This tube then 

 will contain 0.5 c.c. or 5 per cent, of sheep's corpuscles. 

 Several tubes can be prepared in the same way, to 

 furnish sufficient suspension of corpuscles for the test. 

 A convenient method used by us for obtaining 

 blood from the sheep is as follows : In several gradu- 

 ated centrifuge tubes are placed 9 c.c. of 1 per cent, 

 sodium citrate solution in normal saline. The sheep's 

 ear is washed off with alcohol, and one of the large 

 veins severed with a scalpel (Fig. 7) . One c.c. of the 

 blood is now allowed to drop into each of the tubes, 

 the sodium citrate preventing it from clotting. This 

 gives a 5 per cent, suspension of sheep's corpuscles. 

 It is necessary that all serum be removed from the sus- 

 pension, in order to avoid anaphylactic symptoms if 

 for injection into the rabbit, and to remove all 

 complement if the corpuscles are to be used in the test 

 itself. This is accomplished by centrifuging the tubes 

 for 5 or 6 minutes in an electric centrifuge, at the end 

 of which time the corpuscles wiU be found at the 

 bottom. The volume of the corpuscles will vary ac- 

 cording to the length of time used in centrifuging, the 



