312 INFECTION AND IMMUNITY 



is used to prevent clotting and to remove the fibrin. Immediately 

 after receiving the blood into this tube, the wire is twirled between 

 the fingers so that the blood is beaten by the wire as by an egg- 

 beater. At the end of five minutes of continuous agitation, the 

 fibrin adhering in a mass to the wire may be lifted out. The cor- 

 puscles are then washed and centrifugalized in several changes of 

 salt solution to remove all traces of serum, and are finally emulsified 

 in salt solution. 



B. The blood may be taken into a centrifuge tube and imme- 

 diately centrifugalized before clotting has taken place. The plasma 

 is then poured off and the corpuscles are washed with salt solution, 

 as before, to remove the serum. 



C. The blood may be taken directly into a solution containing 

 five-tenths per cent sodium chlorid and one per cent sodium citrate. 

 The corpuscles are concentrated by centrifugalization, the citrate 

 solution is decanted, and corpuscles are washed with salt solution, 

 as before, to remove the serum. 



D. When large quantities of blood are desired, either from man 

 or from an animal, the blood may be received directly into a flask 

 into which a dozen or more glass beads or short pieces of glass 

 tubing have been placed. The flask is shaken for five or ten minutes, 

 immediately after the blood has been taken and, in this way, de- 

 fibrination is accomplished. 



Since, for comparative tests, it is necessary to establish some 

 standard concentration of red blood cells, it is customary in these 

 tests to employ a five per cent emulsion of corpuscles in salt solution. 

 To obtain this, one volume of sediment of washed red blood cells 

 is mixed with nineteen parts of 0.85 per cent salt solution. 10 Such 

 an emulsion, if kept sterile and in the refrigerator, will serve for 

 hemolytic tests for from one to three days. An emulsion should 

 not be used if the supernatant salt solution shows any transparent 

 redness, as this indicates hemolysis. 



If the substance in which hemolysins are to be determined is 

 serum, this should be inactivated by exposure to 56 C. in a water 

 bath, and to each test, complement may be added in the form of 

 fresh guinea-pig or rabbit's serum. No absolute rule for the quan- 



10 The method here given was formerly much employed. It is now the general 

 practice, however, to use one volume of the actual sediment to nineteen volumes 

 of salt solution. 



