182 



PHAGOCYTOSIS OPSONINS AND BACTERIOTROPINS. 



mating the curved end of the latter to the blood (Fig.iS). The straight 

 capillary end of the tube (away from the blood) is then gently warmed in a 

 small flame and sealed. The tube is laid down flat, and allowed to cool; in 

 so doing the blood is sucked back from the unsealed capillary end; next 

 this end may also be sealed in the tip of the flame. The blood then coagu- 

 lates and the serum separates off. The separation of the latter may be 

 hastened by centrifugalization for a short time. 



In order to obtain leucocytes, a small test tube which holds 3 to 4 c.c. is 

 filled 2/3 with a 1.5 per cent, solution of sodium citrate, and about 6 to 7 

 drops of blood from a healthy individual are collected into this solution 

 (Fig. 21). The tube is inverted several times to thoroughly mix the blood so 



FIG. 21. 



FIG. 22. 



that the citrate by precipitating the calcium salts of the blood, effectively 

 prevents coagulation. The suspension is centrifugalized until the corpuscles 

 are thrown down and a distinct white layer (leucocytes) is seen upon the 

 surface of the red cells (Fig. 22). The clear supernant citrate solution is 

 pipetted off, care being taken not to disturb the white layer. Some of the 

 0.85 per cent, saline is added, mixed and again centrifugalized. The wash- 

 ing with normal saline solution is repeated once or twice and as much of the 

 clear liquid as possible is finally removed; the remaining cells are thoroughly 

 mixed and in this form are ready for use. 



The bacterial emulsions with the exception of the tubercle bacillus are 

 made from agar cultures; the growths of gram + cocci may be as old as 

 twenty-four hours, while the coliform organisms and the gram cocci 

 are preferable, if only four to ten hours old, the younger the better. 

 A loopful of culture from an agar tube is thoroughly rubbed up with several 

 drops of salt solution in a watch-glass by means of a small glass pestle. The 

 salt solution is best added very gradually, drop by drop, thus making a more 

 perfect emulsion. This may then be advantageously centrifugalized for a 

 varying period, to bring down the large clumps. The supernatant opalescent 



