IMMUNITY 265 



the cholera vibriones and consequently they retain their original morphology 

 and motility and multiply. 



The phagocytic cells of immunized guinea-pigs contain a more potent cytase 

 and when this is liberated by phagolysis it causes the granular degeneration and 

 loss of motility and arrest of propagation observed. 



Bordet observed that when a sublethal dose of streptococci is injected into 

 the peritoneal cavity of a guinea-pig a high leucocytosis promptly occurs and the 

 cocci are all taken up and destroyed' by the leucocytes. If a lethal dose is 

 injected phagocytosis occurs as before but some cocci escape and these produce a 

 generation more resistant to phagocytosis so that, even though leucocytosis 

 continues high a greater proportion of this second generation escapes destruc- 

 tion, the cocci can multiply faster than the phagocytes can destroy them and 

 general dissemination results. 



FIG. 43. (Citron.) 



FIG. 44. (Citron.) 



In his original investigations of phagocytosis Wright devised a method of 

 studying changes in it, now known as the opsonic index test. The test is 

 made as follows: 



Blood is collected in a capillary tube from the patient, the tube is sealed and 

 put aside to clot (see Fig. 43). Several loopsful of bacteria are removed 

 from a 24- or 48-hour-old culture on solid media and emulsified with normal 

 salt solution; this suspension is drawn into a tube and centrifugalized for a 

 minute to throw down clumps; the supernatant suspension is then removed. 

 Blood is collected from the patient's finger in a capillary tube, half filled with i 

 per cent, sodium citrate in normal salt solution. The tube is shaken to mix 

 the citrate solution and blood, sealed, and centrifugalized until a distinct 

 layer of white cells is seen upon the top of the rods. The white cells are 

 pipetted off and placed in a sterile watch crystal. The patient's serum is 

 poured from the clot into another sterile watch crystal and the bacterial sus- 

 pension is placed in a third watch crystal. 



The bulb of a mixing pipette is compressed and one volume of white cells 

 drawn in by partially releasing the bulb ; the bulb is further released so that the 

 cells retreat from the tip; then a volume of bacteria is drawn into the tube and a 

 bubble of air admitted; finally a volume of patient's serum is taken into the tube. 



