OPSOXIXS AND PHAGOCYTOSIS 169 



been found to be thermolabile (58 to 60 destroys). The immune 

 or specific opsonin is, on the other hand, relatively thermostabile. 

 Opsonic Index. It is sometimes advisable to compare the 

 opsonic content of the serum of a diseased animal with that of a 

 healthy individual. The ratio between the two sera may be 

 determined by the relative effect they have on the rapidity of 

 phagocytic action. It is customary, though not in all cases 

 necessary, to use the leukocytes of the species of animal under 

 investigation. The technic of the operation is as follows: 



Fig. 79. Standardization of bacterial emulsion. A photomicrograph showing 

 the bacteria and the red blood-cells mixed (Miller). 



Preparation of Leukocytes. These may be secured by bleeding 

 into citrate solution (1 per cent, in physiological salt solution) and 

 centrif uging. Pipette off the serum and citrate solution, add physio- 

 logical salt solution, mix, and again centrifuge ; repeat the washing 

 and centrifuging to remove the last traces of serum. Carefully 

 pipette off the upper layer of corpuscles, rich in leukocytes, and 

 keep in a small test-tube. Sometimes the defibrinated whole blood 

 is used. In other cases, particularly with small experimental 

 animals, an intraperitoneal injection of bouillon is made, and the 

 leukocyte-rich exudate removed from the peritoneal cavity in the 

 course of a few hours. 



